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Use EII for #[panic_handler] #159016

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5df0203
Make #[panic_handler] mandatory in all linked artifacts
bjorn3 May 15, 2026
127055b
[WIP] Replace #[lang = "panic_impl"] with #[eii]
bjorn3 May 15, 2026
57fdf54
Fix tests
bjorn3 May 24, 2026
4eb8839
[WIP] Possibly fix clippy
bjorn3 Jun 18, 2026
ca27c25
Remove some dead code
bjorn3 Jul 9, 2026
ce08144
Add docs
bjorn3 Jul 24, 2026
43f6678
Minor tweaks
bjorn3 Jul 24, 2026
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10 changes: 3 additions & 7 deletions compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
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Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
// `#[target_feature]` is incompatible with lang item functions,
// except on WASM where calling target-feature functions is safe (see #84988).
if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
// `#[panic_handler]` is checked first so it takes priority in the diagnostic.
let lang_kind = cx
.all_attrs
.iter()
.find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
if let Some(kind) = lang_kind {
cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
if is_lang_item {
cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
}
}
}
Expand Down
9 changes: 0 additions & 9 deletions compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs
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Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
const PATH: &[Symbol] = &[sym::panic_handler];
const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
const STABILITY: AttributeStability = AttributeStability::Stable;
const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_attr_parsing/src/context.rs
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Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
Single<WithoutArgs<NoMangleParser>>,
Single<WithoutArgs<NoStdParser>>,
Single<WithoutArgs<NonExhaustiveParser>>,
Single<WithoutArgs<PanicHandlerParser>>,
Single<WithoutArgs<PanicRuntimeParser>>,
Single<WithoutArgs<PinV2Parser>>,
Single<WithoutArgs<PreludeImportParser>>,
Expand Down
29 changes: 4 additions & 25 deletions compiler/rustc_attr_parsing/src/session_diagnostics.rs
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Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
"`#[target_feature]` cannot be applied to a {$kind ->
[panic_handler] `#[panic_handler]`
*[other] lang item
} function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
#[primary_span]
pub attr_span: Span,
pub kind: Symbol,
#[label(
"{$kind ->
[panic_handler] `#[panic_handler]`
*[other] lang item
} function is not allowed to have `#[target_feature]`"
)]
#[label("lang item function is not allowed to have `#[target_feature]`")]
pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
"{$name ->
[panic_impl] `#[panic_handler]`
*[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
#[primary_span]
pub attr_span: Span,
pub name: Symbol,
#[label(
"{$name ->
[panic_impl] `#[panic_handler]`
*[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub sig_span: Span,
}

Expand Down
7 changes: 7 additions & 0 deletions compiler/rustc_builtin_macros/src/diagnostics.rs
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Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
#[primary_span]
pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down
3 changes: 3 additions & 0 deletions compiler/rustc_builtin_macros/src/eii.rs
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Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
Some(sym::track_caller) => {
foreign_item_attributes.push(attr);
}
Some(sym::rustc_diagnostic_item) => {
macro_attributes.push(attr.clone());
}
// Doc attributes should be forwarded to the macro and the foreign item, since those are
// the two items you interact with as a user.
// FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_builtin_macros/src/lib.rs
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Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
eii_shared_macro: eii::eii_shared_macro,
global_allocator: global_allocator::expand,
offload_kernel: offload::expand_kernel,
panic_handler: panic_handler::expand,
test: test::expand_test,
test_case: test::expand_test_case,
unsafe_eii: eii::unsafe_eii,
Expand Down
43 changes: 43 additions & 0 deletions compiler/rustc_builtin_macros/src/panic_handler.rs
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@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
ecx: &mut ExtCtxt<'_>,
span: Span,
meta_item: &ast::MetaItem,
mut item: Annotatable,
) -> Vec<Annotatable> {
check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

// Allow using `#[panic_handler]` on an item statement
// FIXME - if we get deref patterns, use them to reduce duplication here
let attrs = if let Annotatable::Item(item) = &mut item {
&mut item.attrs
} else if let Annotatable::Stmt(stmt) = &mut item
&& let StmtKind::Item(item) = &mut stmt.kind
{
&mut item.attrs
} else {
ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
return vec![item];
};

attrs.push(attr::mk_attr_from_item(
&ecx.sess.psess.attr_id_generator,
AttrItem {
unsafety: Safety::Default,
path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
args: AttrArgs::Empty,
span,
},
None,
AttrStyle::Outer,
span,
));

vec![item]
}
14 changes: 14 additions & 0 deletions compiler/rustc_codegen_cranelift/example/mini_core.rs
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Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down
5 changes: 0 additions & 5 deletions compiler/rustc_codegen_gcc/example/alloc_example.rs
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Expand Up@@ -18,11 +18,6 @@ extern "C" {
fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
core::intrinsics::abort();
Expand Down
15 changes: 15 additions & 0 deletions compiler/rustc_codegen_gcc/example/mini_core.rs
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Expand Up@@ -6,6 +6,7 @@
extern_types,
decl_macro,
rustc_attrs,
rustc_private,
transparent_unions,
auto_traits,
freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
}
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
loop {}
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_error_codes/src/error_codes/E0264.md
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Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
#[lang = "panic_impl"] // ok!
#[lang = "eh_personality"] // ok!
fn cake();
}
```
1 change: 0 additions & 1 deletion compiler/rustc_feature/src/builtin_attrs.rs
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Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

// Runtime
sym::windows_subsystem,
sym::panic_handler, // RFC 2070

// Code generation:
sym::inline,
Expand Down
2 changes: 0 additions & 2 deletions compiler/rustc_hir/src/lang_items.rs
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Expand Up@@ -292,9 +292,7 @@ language_item_table! {
ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
/// Constant panic messages, used for codegen of MIR asserts.
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_hir/src/weak_lang_items.rs
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Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
PanicImpl, rust_begin_unwind;
EhPersonality, rust_eh_personality;
}
63 changes: 0 additions & 63 deletions compiler/rustc_hir_typeck/src/check.rs
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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
// we have a recursive call site and do the sadly stabilized fallback to `()`.
fcx.demand_suptype(span, ret_ty, actual_return_ty);

// Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
check_panic_info_fn(tcx, fn_def_id, fn_sig);
}

if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
check_lang_start_fn(tcx, fn_sig, fn_def_id);
}

fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
let span = tcx.def_span(fn_id);

let DefKind::Fn = tcx.def_kind(fn_id) else {
tcx.dcx().span_err(span, "should be a function");
return;
};

let generic_counts = tcx.generics_of(fn_id).own_counts();
if generic_counts.types != 0 {
tcx.dcx().span_err(span, "should have no type parameters");
}
if generic_counts.consts != 0 {
tcx.dcx().span_err(span, "should have no const parameters");
}

let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

// build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
let panic_info_ty = tcx
.type_of(panic_info_did)
.instantiate(
tcx,
&[ty::GenericArg::from(ty::Region::new_bound(
tcx,
ty::INNERMOST,
ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
))],
)
.skip_norm_wip();
let panic_info_ref_ty = Ty::new_imm_ref(
tcx,
ty::Region::new_bound(
tcx,
ty::INNERMOST,
ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
),
panic_info_ty,
);

let bounds = tcx.mk_bound_variable_kinds(&[
ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
]);
let expected_sig = ty::Binder::bind_with_vars(
tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
bounds,
);

let _ = check_function_signature(
tcx,
ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
fn_id.into(),
expected_sig,
);
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
// build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down
3 changes: 1 addition & 2 deletions compiler/rustc_metadata/src/rmeta/decoder.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
)?;
writeln!(
out,
"has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
"has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
root.has_global_allocator,
root.has_alloc_error_handler,
root.has_panic_handler,
root.has_default_lib_allocator
)?;
writeln!(
Expand Down
2 changes: 0 additions & 2 deletions compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
has_global_allocator => { cdata.root.has_global_allocator }
// FIXME: to be replaced with externally_implementable_items below
has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
// FIXME: to be replaced with externally_implementable_items below
has_panic_handler => { cdata.root.has_panic_handler }

externally_implementable_items => {
cdata.get_externally_implementable_items(tcx)
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_metadata/src/rmeta/encoder.rs
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Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
edition: tcx.sess.edition(),
has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
externally_implementable_items,
proc_macro_data,
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_metadata/src/rmeta/mod.rs
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Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
edition: Edition,
has_global_allocator: bool,
has_alloc_error_handler: bool,
has_panic_handler: bool,
has_default_lib_allocator: bool,
externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down
4 changes: 0 additions & 4 deletions compiler/rustc_middle/src/queries.rs
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Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
desc { "checking if the crate has_alloc_error_handler" }
separate_provide_extern
}
query has_panic_handler(_: CrateNum) -> bool {
desc { "checking if the crate has_panic_handler" }
separate_provide_extern
}
query is_profiler_runtime(_: CrateNum) -> bool {
desc { "checking if a crate is `#![profiler_runtime]`" }
separate_provide_extern
Expand Down
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, 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
 blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '
Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]#159016

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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

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7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
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Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

Expand Down

7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
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frag.appendChild(document.createTextNode(part));
} else {
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Array.from(node.childNodes).forEach(highlight);
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if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
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})();
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var __m = "*";
var __re = new RegExp('^' + ".*" + '
Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

Expand Down

7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

Expand Down

7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
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observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

Expand Down

7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
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Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

Expand Down

7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
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style = document.createElement('style');
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/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
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filter: invert(1) hue-rotate(180deg) !important;
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/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
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/* Selection */
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Use EII for #[panic_handler] by bjorn3 · Pull Request #159016 · rust-lang/rust · GitHub
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Use EII for #[panic_handler]
#159016
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5df0203

Make #[panic_handler] mandatory in all linked artifacts


bjorn3 May 15, 2026
127055b

[WIP] Replace #[lang = "panic_impl"] with #[eii]


bjorn3 May 15, 2026
57fdf54

Fix tests


bjorn3 May 24, 2026
4eb8839

[WIP] Possibly fix clippy


bjorn3 Jun 18, 2026
ca27c25

Remove some dead code


bjorn3 Jul 9, 2026
ce08144

Add docs


bjorn3 Jul 24, 2026
43f6678

Minor tweaks


bjorn3 Jul 24, 2026

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10 changes: 3 additions & 7 deletions
compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -566,13 +566,9 @@ impl CombineAttributeParser for TargetFeatureParser {
 // `#[target_feature]` is incompatible with lang item functions,
 // except on WASM where calling target-feature functions is safe (see #84988).
 if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
 // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
 let lang_kind = cx
 .all_attrs
 .iter()
 .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
 if let Some(kind) = lang_kind {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
 let is_lang_item = cx.all_attrs.iter().any(|a| a.word_is(sym::lang));
 if is_lang_item {
 cx.emit_err(TargetFeatureOnLangItem { attr_span, item_span: cx.target_span });
 }
 }
 }
Expand Down

9 changes: 0 additions & 9 deletions
compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -639,15 +639,6 @@ impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
 const PATH: &[Symbol] = &[sym::panic_handler];
 const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
 const STABILITY: AttributeStability = AttributeStability::Stable;
 const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_attr_parsing/src/context.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -285,7 +285,6 @@ attribute_parsers!(
 Single<WithoutArgs<NoMangleParser>>,
 Single<WithoutArgs<NoStdParser>>,
 Single<WithoutArgs<NonExhaustiveParser>>,
 Single<WithoutArgs<PanicHandlerParser>>,
 Single<WithoutArgs<PanicRuntimeParser>>,
 Single<WithoutArgs<PinV2Parser>>,
 Single<WithoutArgs<PreludeImportParser>>,
Expand Down

29 changes: 4 additions & 25 deletions
compiler/rustc_attr_parsing/src/session_diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -108,42 +108,21 @@ pub(crate) struct DocAttributeNotAttribute {
}

#[derive(Diagnostic)]
#[diag(
 "`#[target_feature]` cannot be applied to a {$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function"
)]
#[diag("`#[target_feature]` cannot be applied to a lang item function")]
pub(crate) struct TargetFeatureOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub kind: Symbol,
 #[label(
 "{$kind ->
 [panic_handler] `#[panic_handler]`
 *[other] lang item
 } function is not allowed to have `#[target_feature]`"
 )]
 #[label("lang item function is not allowed to have `#[target_feature]`")]
 pub item_span: Span,
}

#[derive(Diagnostic)]
#[diag(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
} function is not allowed to have `#[track_caller]`"
)]
#[diag("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
pub(crate) struct TrackCallerOnLangItem {
 #[primary_span]
 pub attr_span: Span,
 pub name: Symbol,
 #[label(
 "{$name ->
 [panic_impl] `#[panic_handler]`
 *[other] `{$name}` lang item
 } function is not allowed to have `#[track_caller]`"
 )]
 #[label("`{$name}` lang item function is not allowed to have `#[track_caller]`")]
 pub sig_span: Span,
}

Expand Down

7 changes: 7 additions & 0 deletions
compiler/rustc_builtin_macros/src/diagnostics.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,6 +49,13 @@ pub(crate) struct AllocErrorMustBeFn {
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("panic_handler must be a function")]
pub(crate) struct PanicHandlerMustBeFn {
 #[primary_span]
 pub(crate) span: Span,
}

#[derive(Diagnostic)]
#[diag("macro requires a boolean expression as an argument")]
pub(crate) struct AssertRequiresBoolean {
Expand Down

3 changes: 3 additions & 0 deletions
compiler/rustc_builtin_macros/src/eii.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -226,6 +226,9 @@ fn split_attrs(
 Some(sym::track_caller) => {
 foreign_item_attributes.push(attr);
 }
 Some(sym::rustc_diagnostic_item) => {
 macro_attributes.push(attr.clone());
 }
 // Doc attributes should be forwarded to the macro and the foreign item, since those are
 // the two items you interact with as a user.
 // FIXME: idk yet how EIIs show up in docs, might want to customize
Expand Down

2 changes: 2 additions & 0 deletions
compiler/rustc_builtin_macros/src/lib.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -44,6 +44,7 @@ mod global_allocator;
mod iter;
mod log_syntax;
mod offload;
mod panic_handler;
mod pattern_type;
mod source_util;
mod test;
Expand DownExpand Up@@ -122,6 +123,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
 eii_shared_macro: eii::eii_shared_macro,
 global_allocator: global_allocator::expand,
 offload_kernel: offload::expand_kernel,
 panic_handler: panic_handler::expand,
 test: test::expand_test,
 test_case: test::expand_test_case,
 unsafe_eii: eii::unsafe_eii,
Expand Down

43 changes: 43 additions & 0 deletions
compiler/rustc_builtin_macros/src/panic_handler.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
use rustc_ast::{self as ast, AttrArgs, AttrItem, AttrStyle, Safety, StmtKind, attr};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::{Span, sym};

use crate::diagnostics;
use crate::util::check_builtin_macro_attribute;

pub(crate) fn expand(
 ecx: &mut ExtCtxt<'_>,
 span: Span,
 meta_item: &ast::MetaItem,
 mut item: Annotatable,
) -> Vec<Annotatable> {
 check_builtin_macro_attribute(ecx, meta_item, sym::global_allocator);

 // Allow using `#[panic_handler]` on an item statement
 // FIXME - if we get deref patterns, use them to reduce duplication here
 let attrs = if let Annotatable::Item(item) = &mut item {
 &mut item.attrs
 } else if let Annotatable::Stmt(stmt) = &mut item
 && let StmtKind::Item(item) = &mut stmt.kind
 {
 &mut item.attrs
 } else {
 ecx.dcx().emit_err(diagnostics::PanicHandlerMustBeFn { span: item.span() });
 return vec![item];
 };

 attrs.push(attr::mk_attr_from_item(
 &ecx.sess.psess.attr_id_generator,
 AttrItem {
 unsafety: Safety::Default,
 path: ecx.path_global(span, ecx.std_path(&[sym::panicking, sym::panic_handler])),
 args: AttrArgs::Empty,
 span,
 },
 None,
 AttrStyle::Outer,
 span,
 ));

 vec![item]
}

14 changes: 14 additions & 0 deletions
compiler/rustc_codegen_cranelift/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -835,6 +835,20 @@ struct PanicLocation {
 column: u32,
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[unsafe(no_mangle)]
#[cfg(not(all(windows, target_env = "gnu")))]
pub fn get_tls() -> u8 {
Expand Down

5 changes: 0 additions & 5 deletions
compiler/rustc_codegen_gcc/example/alloc_example.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,11 +18,6 @@ extern "C" {
 fn puts(s: *const u8) -> i32;
}

#[panic_handler]
fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
 core::intrinsics::abort();
}

#[alloc_error_handler]
fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
 core::intrinsics::abort();
Expand Down

15 changes: 15 additions & 0 deletions
compiler/rustc_codegen_gcc/example/mini_core.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
 extern_types,
 decl_macro,
 rustc_attrs,
 rustc_private,
 transparent_unions,
 auto_traits,
 freeze_impls,
Expand DownExpand Up@@ -572,6 +573,20 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 }
}

#[track_caller]
#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
fn panic_misaligned_pointer_dereference(_required: usize, _found: usize) -> ! {
 loop {}
}

#[track_caller]
#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
fn panic_null_pointer_dereference() -> ! {
 loop {}
}

#[lang = "eh_personality"]
fn eh_personality() -> ! {
 loop {}
Expand Down

2 changes: 1 addition & 1 deletion
compiler/rustc_error_codes/src/error_codes/E0264.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -20,7 +20,7 @@ A list of available external lang items is available in
#![allow(internal_features)]

extern "C" {
 #[lang = "panic_impl"] // ok!
 #[lang = "eh_personality"] // ok!
 fn cake();
}
```

1 change: 0 additions & 1 deletion
compiler/rustc_feature/src/builtin_attrs.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -145,7 +145,6 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[

 // Runtime
 sym::windows_subsystem,
 sym::panic_handler, // RFC 2070

 // Code generation:
 sym::inline,
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_hir/src/lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -292,9 +292,7 @@ language_item_table! {
 ConstPanicFmt, sym::const_panic_fmt, const_panic_fmt, Target::Fn, GenericRequirement::None;
 PanicBoundsCheck, sym::panic_bounds_check, panic_bounds_check_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
 PanicInfo, sym::panic_info, panic_info, Target::Struct, GenericRequirement::None;
 PanicLocation, sym::panic_location, panic_location, Target::Struct, GenericRequirement::None;
 PanicImpl, sym::panic_impl, panic_impl, Target::ForeignFn, GenericRequirement::None;
 PanicCannotUnwind, sym::panic_cannot_unwind, panic_cannot_unwind, Target::Fn, GenericRequirement::Exact(0);
 PanicInCleanup, sym::panic_in_cleanup, panic_in_cleanup, Target::Fn, GenericRequirement::Exact(0);
 /// Constant panic messages, used for codegen of MIR asserts.
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_hir/src/weak_lang_items.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -24,6 +24,5 @@ macro_rules! weak_lang_items {
}

weak_lang_items! {
 PanicImpl, rust_begin_unwind;
 EhPersonality, rust_eh_personality;
}

63 changes: 0 additions & 63 deletions
compiler/rustc_hir_typeck/src/check.rs

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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
use std::cell::RefCell;

use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::check::check_function_signature;
use rustc_infer::infer::RegionVariableOrigin;
Expand DownExpand Up@@ -149,75 +148,13 @@ pub(super) fn check_fn<'a, 'tcx>(
 // we have a recursive call site and do the sadly stabilized fallback to `()`.
 fcx.demand_suptype(span, ret_ty, actual_return_ty);

 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
 check_panic_info_fn(tcx, fn_def_id, fn_sig);
 }

 if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
 check_lang_start_fn(tcx, fn_sig, fn_def_id);
 }

 fcx.coroutine_types
}

fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
 let span = tcx.def_span(fn_id);

 let DefKind::Fn = tcx.def_kind(fn_id) else {
 tcx.dcx().span_err(span, "should be a function");
 return;
 };

 let generic_counts = tcx.generics_of(fn_id).own_counts();
 if generic_counts.types != 0 {
 tcx.dcx().span_err(span, "should have no type parameters");
 }
 if generic_counts.consts != 0 {
 tcx.dcx().span_err(span, "should have no const parameters");
 }

 let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, span);

 // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
 let panic_info_ty = tcx
 .type_of(panic_info_did)
 .instantiate(
 tcx,
 &[ty::GenericArg::from(ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
 ))],
 )
 .skip_norm_wip();
 let panic_info_ref_ty = Ty::new_imm_ref(
 tcx,
 ty::Region::new_bound(
 tcx,
 ty::INNERMOST,
 ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
 ),
 panic_info_ty,
 );

 let bounds = tcx.mk_bound_variable_kinds(&[
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
 ]);
 let expected_sig = ty::Binder::bind_with_vars(
 tcx.mk_fn_sig_rust_abi([panic_info_ref_ty], tcx.types.never, fn_sig.safety()),
 bounds,
 );

 let _ = check_function_signature(
 tcx,
 ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
 fn_id.into(),
 expected_sig,
 );
}

fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
 // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`

Expand Down

3 changes: 1 addition & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -781,10 +781,9 @@ impl MetadataBlob {
 )?;
 writeln!(
 out,
 "has_global_allocator {} has_alloc_error_handler {} has_panic_handler {} has_default_lib_allocator {}",
 "has_global_allocator {} has_alloc_error_handler {} has_default_lib_allocator {}",
 root.has_global_allocator,
 root.has_alloc_error_handler,
 root.has_panic_handler,
 root.has_default_lib_allocator
 )?;
 writeln!(
Expand Down

2 changes: 0 additions & 2 deletions
compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -341,8 +341,6 @@ provide! { tcx, def_id, other, cdata,
 has_global_allocator => { cdata.root.has_global_allocator }
 // FIXME: to be replaced with externally_implementable_items below
 has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
 // FIXME: to be replaced with externally_implementable_items below
 has_panic_handler => { cdata.root.has_panic_handler }

 externally_implementable_items => {
 cdata.get_externally_implementable_items(tcx)
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/encoder.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -740,7 +740,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 edition: tcx.sess.edition(),
 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
 has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
 has_default_lib_allocator: find_attr!(attrs, DefaultLibAllocator),
 externally_implementable_items,
 proc_macro_data,
Expand Down

1 change: 0 additions & 1 deletion
compiler/rustc_metadata/src/rmeta/mod.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -257,7 +257,6 @@ pub(crate) struct CrateRoot {
 edition: Edition,
 has_global_allocator: bool,
 has_alloc_error_handler: bool,
 has_panic_handler: bool,
 has_default_lib_allocator: bool,
 externally_implementable_items: LazyArray<EiiMapEncodedKeyValue>,

Expand Down

4 changes: 0 additions & 4 deletions
compiler/rustc_middle/src/queries.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1834,10 +1834,6 @@ rustc_queries! {
 desc { "checking if the crate has_alloc_error_handler" }
 separate_provide_extern
 }
 query has_panic_handler(_: CrateNum) -> bool {
 desc { "checking if the crate has_panic_handler" }
 separate_provide_extern
 }
 query is_profiler_runtime(_: CrateNum) -> bool {
 desc { "checking if a crate is `#![profiler_runtime]`" }
 separate_provide_extern
Expand Down
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