Auto merge of #124228 - compiler-errors:lint-overcaptures, r=oli-obk

Warn against changes in opaque lifetime captures in 2024
Adds a (mostly[^1]) machine-applicable lint `IMPL_TRAIT_OVERCAPTURES` which detects cases where we will capture more lifetimes in edition 2024 than in edition <= 2021, which may lead to erroneous borrowck errors.
This lint is gated behind the `precise_capturing` feature gate and marked `Allow` for now.
[^1]: Except when there are APITs -- I may work on that soon
r? oli-obk

Author: bors

compiler/rustc_ast_lowering/src/lib.rs

@@ -1407,7 +1407,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  bounds,
  fn_kind,
  itctx,
- precise_capturing.as_deref().map(|(args,_)| args.as_slice()),
+ precise_capturing.as_deref().map(|(args,span)| (args.as_slice(),*span)),
 ),
 ImplTraitContext::Universal => {
 ifletSome(&(_, span)) = precise_capturing.as_deref(){
@@ -1523,7 +1523,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 bounds:&GenericBounds,
 fn_kind:Option<FnDeclKind>,
 itctx:ImplTraitContext,
-precise_capturing_args:Option<&[PreciseCapturingArg]>,
+precise_capturing_args:Option<(&[PreciseCapturingArg],Span)>,
 ) -> hir::TyKind<'hir>{
 // Make sure we know that some funky desugaring has been going on here.
 // This is a first: there is code in other places like for loop
@@ -1533,7 +1533,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span,None);
 
 let captured_lifetimes_to_duplicate =
-ifletSome(precise_capturing) = precise_capturing_args {
+ifletSome((precise_capturing, _)) = precise_capturing_args {
 // We'll actually validate these later on; all we need is the list of
 // lifetimes to duplicate during this portion of lowering.
  precise_capturing
@@ -1607,7 +1607,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 captured_lifetimes_to_duplicate:FxIndexSet<Lifetime>,
 span:Span,
 opaque_ty_span:Span,
-precise_capturing_args:Option<&[PreciseCapturingArg]>,
+precise_capturing_args:Option<(&[PreciseCapturingArg],Span)>,
 lower_item_bounds:implFnOnce(&mutSelf) -> &'hir[hir::GenericBound<'hir>],
 ) -> hir::TyKind<'hir>{
 let opaque_ty_def_id = self.create_def(
@@ -1698,8 +1698,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  this.with_remapping(captured_to_synthesized_mapping, |this| {
 (
 lower_item_bounds(this),
- precise_capturing_args.map(|precise_capturing| {
- this.lower_precise_capturing_args(precise_capturing)
+ precise_capturing_args.map(|(precise_capturing, span)| {
+(
+ this.lower_precise_capturing_args(precise_capturing),
+ this.lower_span(span),
+)
 }),
 )
 });

compiler/rustc_hir/src/hir.rs

@@ -2631,7 +2631,7 @@ pub struct OpaqueTy<'hir> {
 /// lowered as an associated type.
 pubin_trait:bool,
 /// List of arguments captured via `impl use<'a, P, ...> Trait` syntax.
-pubprecise_capturing_args:Option<&'hir[PreciseCapturingArg<'hir>]>,
+pubprecise_capturing_args:Option<(&'hir[PreciseCapturingArg<'hir>],Span)>,
 }
 
 #[derive(Debug,Clone,Copy,HashStable_Generic)]
@@ -2641,6 +2641,15 @@ pub enum PreciseCapturingArg<'hir> {
 Param(PreciseCapturingNonLifetimeArg),
 }
 
+implPreciseCapturingArg<'_>{
+pubfnhir_id(self) -> HirId{
+matchself{
+PreciseCapturingArg::Lifetime(lt) => lt.hir_id,
+PreciseCapturingArg::Param(param) => param.hir_id,
+}
+}
+}
+
 /// We need to have a [`Node`] for the [`HirId`] that we attach the type/const param
 /// resolution to. Lifetimes don't have this problem, and for them, it's actually
 /// kind of detrimental to use a custom node type versus just using [`Lifetime`],

compiler/rustc_hir/src/intravisit.rs

@@ -533,7 +533,7 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item<'v>) -> V::
 try_visit!(visitor.visit_id(item.hir_id()));
 try_visit!(walk_generics(visitor, generics));
 walk_list!(visitor, visit_param_bound, bounds);
-ifletSome(precise_capturing_args) = precise_capturing_args {
+ifletSome((precise_capturing_args, _)) = precise_capturing_args {
 for arg in precise_capturing_args {
 try_visit!(visitor.visit_precise_capturing_arg(arg));
 }

compiler/rustc_hir_analysis/src/check/check.rs

@@ -486,7 +486,7 @@ fn sanity_check_found_hidden_type<'tcx>(
 fncheck_opaque_precise_captures<'tcx>(tcx:TyCtxt<'tcx>,opaque_def_id:LocalDefId){
 let hir::OpaqueTy{ precise_capturing_args, .. } =
 *tcx.hir_node_by_def_id(opaque_def_id).expect_item().expect_opaque_ty();
-letSome(precise_capturing_args) = precise_capturing_args else{
+letSome((precise_capturing_args, _)) = precise_capturing_args else{
 // No precise capturing args; nothing to validate
 return;
 };

compiler/rustc_lint/messages.ftl

@@ -269,6 +269,17 @@ lint_identifier_uncommon_codepoints = identifier contains {$codepoints_len ->
 
 lint_ignored_unless_crate_specified = {$level}({$name}) is ignored unless specified at crate level
 
+lint_impl_trait_overcaptures = `{$self_ty}` will capture more lifetimes than possibly intended in edition 2024
+.note = specifically, {$num_captured->
+ [one] this lifetime is
+ *[other] these lifetimes are
+} in scope but not mentioned in the type's bounds
+.note2 = all lifetimes in scope will be captured by `impl Trait`s in edition 2024
+.suggestion = use the precise capturing `use<...>` syntax to make the captures explicit
+
+lint_impl_trait_redundant_captures = all possible in-scope parameters are already captured, so `use<...>` syntax is redundant
+.suggestion = remove the `use<...>` syntax
+
 lint_improper_ctypes = `extern` {$desc} uses type `{$ty}`, which is not FFI-safe
 .label = not FFI-safe
 .note = the type is defined here