Treat inherent methods in const impl blocks as const

Author: oli-obk

compiler/rustc_const_eval/src/const_eval/fn_queries.rs

@@ -8,6 +8,9 @@ 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::Trait => {
             if tcx.is_const_trait(parent_id.into()) {
                 hir::Constness::Const

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

@@ -0,0 +1,22 @@
+#![feature(const_trait_impl)]
+
+struct Foo<T>(T);
+
+const trait Trait {
+    fn method() {}
+}
+
+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
+    }
+}
+
+const _: () = Foo::<()>::bar();
+
+fn main() {
+    Foo::<()>::bar();
+}

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

@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `T: [const] Trait` is not satisfied
+  --> $DIR/const-impl-inherent-bounds.rs:13:9
+   |
+LL |         T::method();
+   |         ^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

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

@@ -0,0 +1,15 @@
+#![feature(const_trait_impl)]
+
+//@ check-pass
+
+struct Foo;
+
+const impl Foo {
+    fn bar() {}
+}
+
+const _: () = Foo::bar();
+
+fn main() {
+    Foo::bar();
+}