Auto merge of #148434 - oli-obk:inherent-const-impl, r=fee1-dead

Inherent const impl
Some constifications are annoying because we need to repeat `T: Trait` bounds from an impl block on the individual constified `const fn`s as `T: [const] Trait`. We've brainstormed solutions before, and one would be to have separate `const impl` blocks or sth. However the final syntax will look, I decided to just impl this syntax and either have sth nice on nightly to work with or at least move the discussion along.
Also interacts with the discussion around `impl const Trait for Type` vs `const impl Trait for Type`, as we may want to use the latter to keep inherent and trait impls in sync (unless we come up with even another scheme).
* [ ] rustdoc + tests
* [ ] macro stability /regression tests
r? `@fee1-dead`
cc `@traviscross` `@rust-lang/project-const-traits`

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }
 

compiler/rustc_ast/src/ast.rs

@@ -3699,6 +3699,7 @@ pub struct TyAlias {
 #[derive(Clone,Encodable,Decodable,Debug)]
 pubstructImpl{
 pubgenerics:Generics,
+pubconstness:Const,
 pubof_trait:Option<Box<TraitImplHeader>>,
 pubself_ty:Box<Ty>,
 pubitems:ThinVec<Box<AssocItem>>,
@@ -3708,7 +3709,6 @@ pub struct Impl {
 pubstructTraitImplHeader{
 pubdefaultness:Defaultness,
 pubsafety:Safety,
-pubconstness:Const,
 pubpolarity:ImplPolarity,
 pubtrait_ref:TraitRef,
 }
@@ -4103,9 +4103,9 @@ mod size_asserts {
 static_assert_size!(GenericArg,24);
 static_assert_size!(GenericBound,88);
 static_assert_size!(Generics,40);
-static_assert_size!(Impl,64);
-static_assert_size!(Item,136);
-static_assert_size!(ItemKind,72);
+static_assert_size!(Impl,80);
+static_assert_size!(Item,152);
+static_assert_size!(ItemKind,88);
 static_assert_size!(LitKind,24);
 static_assert_size!(Local,96);
 static_assert_size!(MetaItemLit,40);
@@ -4116,7 +4116,7 @@ mod size_asserts {
 static_assert_size!(PathSegment,24);
 static_assert_size!(Stmt,32);
 static_assert_size!(StmtKind,16);
-static_assert_size!(TraitImplHeader,80);
+static_assert_size!(TraitImplHeader,72);
 static_assert_size!(Ty,64);
 static_assert_size!(TyKind,40);
 // tidy-alphabetical-end

compiler/rustc_ast/src/visit.rs

@@ -934,11 +934,11 @@ macro_rules! common_visitor_and_walkers {
 }
 
  impl_walkable!(|&$($mut)? $($lt)? self:Impl, vis:&mutV| {
-letImpl{ generics, of_trait, self_ty, items } = self;
+letImpl{ generics, of_trait, self_ty, items, constness: _} = self;
  try_visit!(vis.visit_generics(generics));
 ifletSome(box of_trait) = of_trait {
-letTraitImplHeader{ defaultness, safety,constness,polarity, trait_ref } = of_trait;
- visit_visitable!($($mut)? vis, defaultness, safety,constness,polarity, trait_ref);
+letTraitImplHeader{ defaultness, safety, polarity, trait_ref } = of_trait;
+ visit_visitable!($($mut)? vis, defaultness, safety, polarity, trait_ref);
 }
  try_visit!(vis.visit_ty(self_ty));
  visit_visitable_with!($($mut)? vis, items,AssocCtxt::Impl{ of_trait: of_trait.is_some()});

compiler/rustc_ast_lowering/src/item.rs

@@ -344,6 +344,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  of_trait,
 self_ty: ty,
 items: impl_items,
+ constness,
 }) => {
 // Lower the "impl header" first. This ordering is important
 // for in-band lifetimes! Consider `'a` here:
@@ -377,11 +378,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
 .arena
 .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
+let constness = self.lower_constness(*constness);
+
  hir::ItemKind::Impl(hir::Impl{
  generics,
  of_trait,
 self_ty: lowered_ty,
 items: new_impl_items,
+ constness,
 })
 }
 ItemKind::Trait(box Trait{
@@ -954,9 +958,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 &mutself,
 trait_impl_header:&TraitImplHeader,
 ) -> &'hir hir::TraitImplHeader<'hir>{
-letTraitImplHeader{ constness, safety, polarity, defaultness,ref trait_ref } =
-*trait_impl_header;
-let constness = self.lower_constness(constness);
+letTraitImplHeader{ safety, polarity, defaultness,ref trait_ref } = *trait_impl_header;
 let safety = self.lower_safety(safety, hir::Safety::Safe);
 let polarity = match polarity {
 ImplPolarity::Positive => ImplPolarity::Positive,
@@ -979,7 +981,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
 );
 
 self.arena.alloc(hir::TraitImplHeader{
- constness,
  safety,
  polarity,
  defaultness,

compiler/rustc_ast_passes/messages.ftl

@@ -204,6 +204,11 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
+ast_passes_impl_fn_const =
+ redundant `const` fn marker in const impl
+.parent_constness = this declares all associated functions implicitly const
+.label = remove the `const`
+
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
 .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -48,15 +48,17 @@ enum SelfSemantic {
 No,
 }
 
-enumTraitOrTraitImpl{
+enumTraitOrImpl{
 Trait{vis:Span,constness:Const},
 TraitImpl{constness:Const,polarity:ImplPolarity,trait_ref_span:Span},
+Impl{constness:Const},
 }
 
-implTraitOrTraitImpl{
+implTraitOrImpl{
 fnconstness(&self) -> Option<Span>{
 matchself{
 Self::Trait{constness:Const::Yes(span), .. }
+ | Self::Impl{constness:Const::Yes(span), .. }
  | Self::TraitImpl{constness:Const::Yes(span), .. } => Some(*span),
  _ => None,
 }
@@ -70,7 +72,7 @@ struct AstValidator<'a> {
 /// The span of the `extern` in an `extern { ... }` block, if any.
 extern_mod_span:Option<Span>,
 
-outer_trait_or_trait_impl:Option<TraitOrTraitImpl>,
+outer_trait_or_trait_impl:Option<TraitOrImpl>,
 
 has_proc_macro_decls:bool,
 
@@ -93,27 +95,20 @@ struct AstValidator<'a> {
 }
 
 impl<'a>AstValidator<'a>{
-fnwith_in_trait_impl(
+fnwith_in_trait_or_impl(
 &mutself,
-trait_:Option<(Const,ImplPolarity,&'aTraitRef)>,
+in_trait_or_impl:Option<TraitOrImpl>,
 f:implFnOnce(&mutSelf),
 ){
-let old = mem::replace(
-&mutself.outer_trait_or_trait_impl,
- trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl{
- constness,
- polarity,
-trait_ref_span: trait_ref.path.span,
-}),
-);
+let old = mem::replace(&mutself.outer_trait_or_trait_impl, in_trait_or_impl);
 f(self);
 self.outer_trait_or_trait_impl = old;
 }
 
 fnwith_in_trait(&mutself,vis:Span,constness:Const,f:implFnOnce(&mutSelf)){
 let old = mem::replace(
 &mutself.outer_trait_or_trait_impl,
-Some(TraitOrTraitImpl::Trait{ vis, constness }),
+Some(TraitOrImpl::Trait{ vis, constness }),
 );
 f(self);
 self.outer_trait_or_trait_impl = old;
@@ -247,14 +242,28 @@ impl<'a> AstValidator<'a> {
 }
 }
 
-fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrTraitImpl){
+fncheck_impl_fn_not_const(&self,constness:Const,parent_constness:Const){
+letConst::Yes(span) = constness else{
+return;
+};
+
+let span = self.sess.source_map().span_extend_while_whitespace(span);
+
+letConst::Yes(parent_constness) = parent_constness else{
+return;
+};
+
+self.dcx().emit_err(errors::ImplFnConst{ span, parent_constness });
+}
+
+fncheck_trait_fn_not_const(&self,constness:Const,parent:&TraitOrImpl){
 letConst::Yes(span) = constness else{
 return;
 };
 
 let const_trait_impl = self.features.const_trait_impl();
 let make_impl_const_sugg = if const_trait_impl
- && letTraitOrTraitImpl::TraitImpl{
+ && letTraitOrImpl::TraitImpl{
 constness:Const::No,
 polarity:ImplPolarity::Positive,
  trait_ref_span,
@@ -269,7 +278,7 @@ impl<'a> AstValidator<'a> {
 let map = self.sess.source_map();
 
 let make_trait_const_sugg = if const_trait_impl
- && let&TraitOrTraitImpl::Trait{ vis,constness: ast::Const::No} = parent
+ && let&TraitOrImpl::Trait{ vis,constness: ast::Const::No} = parent
 {
 Some(map.span_extend_while_whitespace(vis).shrink_to_hi())
 }else{
@@ -279,7 +288,7 @@ impl<'a> AstValidator<'a> {
 let parent_constness = parent.constness();
 self.dcx().emit_err(errors::TraitFnConst{
  span,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
 const_context_label: parent_constness,
 remove_const_sugg:(
  map.span_extend_while_whitespace(span),
@@ -295,7 +304,7 @@ impl<'a> AstValidator<'a> {
 });
 }
 
-fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrTraitImpl){
+fncheck_async_fn_in_const_trait_or_impl(&self,sig:&FnSig,parent:&TraitOrImpl){
 letSome(const_keyword) = parent.constness()else{return};
 
 letSome(CoroutineKind::Async{span: async_keyword, .. }) = sig.header.coroutine_kind
@@ -305,7 +314,7 @@ impl<'a> AstValidator<'a> {
 
 self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl{
  async_keyword,
-in_impl:matches!(parent,TraitOrTraitImpl::TraitImpl{ .. }),
+in_impl:matches!(parent,TraitOrImpl::TraitImpl{ .. }),
  const_keyword,
 });
 }
@@ -1070,14 +1079,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 match&item.kind{
 ItemKind::Impl(Impl{
  generics,
+ constness,
 of_trait:
-Some(box TraitImplHeader{
- safety,
- polarity,
-defaultness: _,
- constness,
-trait_ref: t,
-}),
+Some(box TraitImplHeader{ safety, polarity,defaultness: _,trait_ref: t }),
  self_ty,
  items,
 }) => {
@@ -1105,24 +1109,46 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 self.visit_trait_ref(t);
 self.visit_ty(self_ty);
 
-self.with_in_trait_impl(Some((*constness,*polarity, t)), |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:true});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::TraitImpl{
+constness:*constness,
+polarity:*polarity,
+trait_ref_span: t.path.span,
+}),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:true}
+);
+},
+);
 }
-ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items }) => {
+ItemKind::Impl(Impl{ generics,of_trait:None, self_ty, items, constness}) => {
 self.visit_attrs_vis(&item.attrs,&item.vis);
 self.visibility_not_permitted(
 &item.vis,
  errors::VisibilityNotPermittedNote::IndividualImplItems,
 );
 
-self.with_tilde_const(Some(TildeConstReason::Impl{span: item.span}), |this| {
- this.visit_generics(generics)
-});
+let disallowed = matches!(constness, ast::Const::No)
+.then(|| TildeConstReason::Impl{span: item.span});
+
+self.with_tilde_const(disallowed, |this| this.visit_generics(generics));
+
 self.visit_ty(self_ty);
-self.with_in_trait_impl(None, |this| {
-walk_list!(this, visit_assoc_item, items,AssocCtxt::Impl{ of_trait:false});
-});
+self.with_in_trait_or_impl(
+Some(TraitOrImpl::Impl{constness:*constness }),
+ |this| {
+walk_list!(
+ this,
+ visit_assoc_item,
+ items,
+AssocCtxt::Impl{ of_trait:false}
+);
+},
+);
 }
 ItemKind::Fn(
  func @ boxFn{
@@ -1240,7 +1266,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  this.visit_generics(generics);
 walk_list!(this, visit_param_bound, bounds,BoundKind::SuperTraits)
 });
-self.with_in_trait(item.vis.span,*constness, |this| {
+self.with_in_trait(item.span,*constness, |this| {
 walk_list!(this, visit_assoc_item, items,AssocCtxt::Trait);
 });
 }
@@ -1610,7 +1636,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
  && self
 .outer_trait_or_trait_impl
 .as_ref()
-.and_then(TraitOrTraitImpl::constness)
+.and_then(TraitOrImpl::constness)
 .is_some();
 
 let disallowed = (!tilde_const_allowed).then(|| match fk {
@@ -1677,20 +1703,31 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 );
 }
 
-ifletSome(parent) = &self.outer_trait_or_trait_impl{
-self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
-ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
-self.check_trait_fn_not_const(sig.header.constness, parent);
-self.check_async_fn_in_const_trait_or_impl(sig, parent);
+match&self.outer_trait_or_trait_impl{
+Some(parent @ (TraitOrImpl::Trait{ .. } | TraitOrImpl::TraitImpl{ .. })) => {
+self.visibility_not_permitted(
+&item.vis,
+ errors::VisibilityNotPermittedNote::TraitImpl,
+);
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_trait_fn_not_const(sig.header.constness, parent);
+self.check_async_fn_in_const_trait_or_impl(sig, parent);
+}
+}
+Some(TraitOrImpl::Impl{ constness }) => {
+ifletAssocItemKind::Fn(boxFn{ sig, .. }) = &item.kind{
+self.check_impl_fn_not_const(sig.header.constness,*constness);
+}
 }
+None => {}
 }
 
 ifletAssocItemKind::Const(ci) = &item.kind{
 self.check_item_named(ci.ident,"const");
 }
 
 let parent_is_const =
-self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrTraitImpl::constness).is_some();
+self.outer_trait_or_trait_impl.as_ref().and_then(TraitOrImpl::constness).is_some();
 
 match&item.kind{
 AssocItemKind::Fn(func)
@@ -1704,19 +1741,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 }
 AssocItemKind::Type(_) => {
 let disallowed = (!parent_is_const).then(|| matchself.outer_trait_or_trait_impl{
-Some(TraitOrTraitImpl::Trait{ .. }) => {
+Some(TraitOrImpl::Trait{ .. }) => {
 TildeConstReason::TraitAssocTy{span: item.span}
 }
-Some(TraitOrTraitImpl::TraitImpl{ .. }) => {
+Some(TraitOrImpl::TraitImpl{ .. }) => {
 TildeConstReason::TraitImplAssocTy{span: item.span}
 }
-None => TildeConstReason::InherentAssocTy{span: item.span},
+Some(TraitOrImpl::Impl{ .. }) | None => {
+TildeConstReason::InherentAssocTy{span: item.span}
+}
 });
 self.with_tilde_const(disallowed, |this| {
- this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
+ this.with_in_trait_or_impl(None, |this| {
+ visit::walk_assoc_item(this, item, ctxt)
+})
 })
 }
- _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
+ _ => self.with_in_trait_or_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
 }
 }