Auto merge of #135634 - joboet:trivial-clone, r=Mark-Simulacrum

stop specializing on `Copy`
fixes#132442
`std` specializes on `Copy` to optimize certain library functions such as `clone_from_slice`. This is unsound, however, as the `Copy` implementation may not be always applicable because of lifetime bounds, which specialization does not take into account; the result being that values are copied even though they are not `Copy`. For instance, this code:
```rust
struct SometimesCopy<'a>(&'a Cell<bool>);
impl<'a> Clone for SometimesCopy<'a> {
fn clone(&self) -> Self {
self.0.set(true);
Self(self.0)
}
}
impl Copy for SometimesCopy<'static> {}
let clone_called = Cell::new(false);
// As SometimesCopy<'clone_called> is not 'static, this must run `clone`,
// setting the value to `true`.
let _ = [SometimesCopy(&clone_called)].clone();
assert!(clone_called.get());
```
should not panic, but does ([playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=6be7a48cad849d8bd064491616fdb43c)).
To solve this, this PR introduces a new `unsafe` trait: `TrivialClone`. This trait may be implemented whenever the `Clone` implementation is equivalent to copying the value (so e.g. `fn clone(&self) -> Self { *self }`). Because of lifetime erasure, there is no way for the `Clone` implementation to observe lifetime bounds, meaning that even if the `TrivialClone` has stricter bounds than the `Clone` implementation, its invariant still holds. Therefore, it is sound to specialize on `TrivialClone`.
I've changed all `Copy` specializations in the standard library to specialize on `TrivialClone` instead. Unfortunately, the unsound `#[rustc_unsafe_specialization_marker]` attribute on `Copy` cannot be removed in this PR as `hashbrown` still depends on it. I'll make a PR updating `hashbrown` once this lands.
With `Copy` no longer being considered for specialization, this change alone would result in the standard library optimizations not being applied for user types unaware of `TrivialClone`. To avoid this and restore the optimizations in most cases, I have changed the expansion of `#[derive(Clone)]`: Currently, whenever both `Clone` and `Copy` are derived, the `clone` method performs a copy of the value. With this PR, the derive macro also adds a `TrivialClone` implementation to make this case observable using specialization. I anticipate that most users will use `#[derive(Clone, Copy)]` whenever both are applicable, so most users will still profit from the library optimizations.
Unfortunately, Hyrum's law applies to this PR: there are some popular crates which rely on the precise specialization behaviour of `core` to implement "specialization at home", e.g. [`libAFL`](https://github.com/AFLplusplus/LibAFL/blob/89cff637025c1652c24e8d97a30a2e3d01f187a4/libafl_bolts/src/tuples.rs#L27-L49). I have no remorse for breaking such horrible code, but perhaps we should open other, better ways to satisfy their needs – for example by dropping the `'static` bound on `TypeId::of`...

Author: bors

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::Span;
 
@@ -24,6 +24,8 @@ pub(crate) fn expand_deriving_copy(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);
@@ -48,6 +50,8 @@ pub(crate) fn expand_deriving_const_param_ty(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,VariantData};
+use rustc_ast::{selfas ast,Generics,ItemKind,MetaItem,Safety,VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
-use rustc_span::{Ident,Span, kw, sym};
+use rustc_span::{DUMMY_SP,Ident,Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 usecrate::deriving::generic::ty::*;
@@ -68,6 +68,29 @@ pub(crate) fn expand_deriving_clone(
  _ => cx.dcx().span_bug(span,"`#[derive(Clone)]` on trait item or impl item"),
 }
 
+// If the clone method is just copying the value, also mark the type as
+// `TrivialClone` to allow some library optimizations.
+if is_simple {
+let trivial_def = TraitDef{
+ span,
+path:path_std!(clone::TrivialClone),
+skip_path_as_bound:false,
+needs_copy_as_bound_if_packed:true,
+additional_bounds: bounds.clone(),
+supports_unions:true,
+methods:Vec::new(),
+associated_types:Vec::new(),
+ is_const,
+is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Unsafe(DUMMY_SP),
+// `TrivialClone` is not part of an API guarantee, so it shouldn't
+// appear in rustdoc output.
+document:false,
+};
+
+ trivial_def.expand_ext(cx, mitem, item, push,true);
+}
+
 let trait_def = TraitDef{
  span,
 path:path_std!(clone::Clone),
@@ -88,6 +111,8 @@ pub(crate) fn expand_deriving_clone(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand_ext(cx, mitem, item, push, is_simple)

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,MetaItem};
+use rustc_ast::{selfas ast,MetaItem,Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
@@ -44,6 +44,8 @@ pub(crate) fn expand_deriving_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand_ext(cx, mitem, item, push,true)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -35,6 +35,8 @@ pub(crate) fn expand_deriving_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  trait_def.expand(cx, mitem, item, push)

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability};
+use rustc_ast::{BinOpKind,BorrowKind,Expr,ExprKind,MetaItem,Mutability,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -30,6 +30,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
 is_const:false,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  structural_trait_def.expand(cx, mitem, item, push);
 
@@ -59,6 +61,8 @@ pub(crate) fn expand_deriving_partial_eq(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind};
+use rustc_ast::{ExprKind,ItemKind,MetaItem,PatKind,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_span::{Ident,Span, sym};
 use thin_vec::thin_vec;
@@ -65,6 +65,8 @@ pub(crate) fn expand_deriving_partial_ord(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{selfas ast,EnumDef,MetaItem};
+use rustc_ast::{selfas ast,EnumDef,MetaItem,Safety};
 use rustc_expand::base::{Annotatable,ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident,Span,Symbol, sym};
@@ -42,6 +42,8 @@ pub(crate) fn expand_deriving_debug(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef,VariantData, attr};
+use rustc_ast::{selfas ast,EnumDef,Safety,VariantData, attr};
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{ErrorGuaranteed,Ident,Span, kw, sym};
 use smallvec::SmallVec;
@@ -52,6 +51,8 @@ pub(crate) fn expand_deriving_default(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
  trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/from.rs

@@ -1,5 +1,5 @@
 use rustc_ast as ast;
-use rustc_ast::{ItemKind,VariantData};
+use rustc_ast::{ItemKind,Safety,VariantData};
 use rustc_errors::MultiSpan;
 use rustc_expand::base::{Annotatable,DummyResult,ExtCtxt};
 use rustc_span::{Ident,Span, kw, sym};
@@ -127,6 +127,8 @@ pub(crate) fn expand_deriving_from(
 associated_types:Vec::new(),
  is_const,
 is_staged_api_crate: cx.ecfg.features.staged_api(),
+safety:Safety::Default,
+document:true,
 };
 
  from_trait_def.expand(cx, mitem, annotatable, push);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -225,6 +225,12 @@ pub(crate) struct TraitDef<'a> {
 pubis_const:bool,
 
 pubis_staged_api_crate:bool,
+
+/// The safety of the `impl`.
+pubsafety:Safety,
+
+/// Whether the added `impl` should appear in rustdoc output.
+pubdocument:bool,
 }
 
 pub(crate)structMethodDef<'a>{
@@ -826,13 +832,17 @@ impl<'a> TraitDef<'a> {
 )
 }
 
+if !self.document{
+ attrs.push(cx.attr_nested_word(sym::doc, sym::hidden,self.span));
+}
+
  cx.item(
 self.span,
  attrs,
  ast::ItemKind::Impl(ast::Impl{
 generics: trait_generics,
 of_trait:Some(Box::new(ast::TraitImplHeader{
-safety:ast::Safety::Default,
+safety:self.safety,
 polarity: ast::ImplPolarity::Positive,
 defaultness: ast::Defaultness::Final,
 constness:ifself.is_const{