Collect const_conditions for inherent impls

Author: oli-obk

compiler/rustc_const_eval/src/const_eval/fn_queries.rs

@@ -8,9 +8,7 @@ fn parent_impl_or_trait_constness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::C
     let parent_id = tcx.local_parent(def_id);
     match tcx.def_kind(parent_id) {
         DefKind::Impl { of_trait: true } => tcx.impl_trait_header(parent_id).constness,
-        DefKind::Impl { of_trait: false } => {
-            tcx.hir_node_by_def_id(parent_id).expect_item().expect_impl().constness
-        }
+        DefKind::Impl { of_trait: false } => tcx.constness(parent_id),
         DefKind::Trait => {
             if tcx.is_const_trait(parent_id.into()) {
                 hir::Constness::Const
@@ -33,6 +31,7 @@ fn constness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::Constness {
             hir::Constness::NotConst
         }
         hir::Node::Expr(e) if let hir::ExprKind::Closure(c) = e.kind => c.constness,
+        hir::Node::Item(i) if let hir::ItemKind::Impl(impl_) = i.kind => impl_.constness,
         _ => {
             if let Some(fn_kind) = node.fn_kind() {
                 if fn_kind.constness() == hir::Constness::Const {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1315,7 +1315,11 @@ fn should_encode_fn_sig(def_kind: DefKind) -> bool {
 
 fn should_encode_constness(def_kind: DefKind) -> bool {
     match def_kind {
-        DefKind::Fn | DefKind::AssocFn | DefKind::Closure | DefKind::Ctor(_, CtorKind::Fn) => true,
+        DefKind::Fn
+        | DefKind::AssocFn
+        | DefKind::Closure
+        | DefKind::Ctor(_, CtorKind::Fn)
+        | DefKind::Impl { of_trait: false } => true,
 
         DefKind::Struct
         | DefKind::Union

compiler/rustc_middle/src/ty/mod.rs

@@ -2151,6 +2151,7 @@ impl<'tcx> TyCtxt<'tcx> {
                 header.constness == hir::Constness::Const
                     && self.is_const_trait(header.trait_ref.skip_binder().def_id)
             }
+            DefKind::Impl { of_trait: false } => self.constness(def_id) == hir::Constness::Const,
             DefKind::Fn | DefKind::Ctor(_, CtorKind::Fn) => {
                 self.constness(def_id) == hir::Constness::Const
             }
@@ -2189,7 +2190,6 @@ impl<'tcx> TyCtxt<'tcx> {
                 false
             }
             DefKind::Ctor(_, CtorKind::Const)
-            | DefKind::Impl { of_trait: false }
             | DefKind::Mod
             | DefKind::Struct
             | DefKind::Union

tests/ui/traits/const-traits/const-impl-inherent-bounds.rs

@@ -1,4 +1,7 @@
 #![feature(const_trait_impl)]
+//! Test that we can actually use `[const] Trait` bounds written on the impl block
+
+//@ check-pass
 
 struct Foo<T>(T);
 
@@ -11,7 +14,6 @@ const impl Trait for () {}
 const impl<T: [const] Trait> Foo<T> {
     fn bar() {
         T::method();
-        //~^ ERROR: the trait bound `T: [const] Trait` is not satisfied
     }
 }