Fix call-generic-method-nonconst test

compiler/rustc_hir/src/hir.rs

@@ -3261,7 +3261,7 @@ impl<'hir> Node<'hir> {
         }
     }
 
-    /// Returns `Constness::Const` when this node is a const fn/impl.
+    /// Returns `Constness::Const` when this node is a const fn/impl/item.
     pub fn constness(&self) -> Constness {
         match self {
             Node::Item(Item {
@@ -3278,6 +3278,10 @@ impl<'hir> Node<'hir> {
             })
             | Node::Item(Item { kind: ItemKind::Impl(Impl { constness, .. }), .. }) => *constness,
 
+            Node::Item(Item { kind: ItemKind::Const(..), .. })
+            | Node::TraitItem(TraitItem { kind: TraitItemKind::Const(..), .. })
+            | Node::ImplItem(ImplItem { kind: ImplItemKind::Const(..), .. }) => Constness::Const,
+
             _ => Constness::NotConst,
         }
     }

src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.rs

@@ -1,7 +1,5 @@
-// FIXME(jschievink): this is not rejected correctly (only when the non-const impl is actually used)
-// ignore-test
-
 #![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
 
 struct S;
 

src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.stderr

@@ -0,0 +1,14 @@
+error[E0277]: can't compare `S` with `S`
+  --> $DIR/call-generic-method-nonconst.rs:19:34
+   |
+LL | const fn equals_self<T: PartialEq>(t: &T) -> bool {
+   |                         --------- required by this bound in `equals_self`
+...
+LL | pub const EQ: bool = equals_self(&S);
+   |                                  ^^ no implementation for `S == S`
+   |
+   = help: the trait `PartialEq` is not implemented for `S`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.