Fix validation of constant items

gcc/rust/ChangeLog:

	* checks/errors/rust-ast-validation.cc
	(ASTValidation::visit): Allow constant items lacking expressions
	if and only if they're associated with a trait definition, not a
	trait implementation.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3541-1.rs: New test.
	* rust/compile/issue-3541-2.rs: Likewise.

Signed-off-by: Owen Avery <[email protected]>

Author: powerboat9

gcc/rust/checks/errors/rust-ast-validation.cc

@@ -56,7 +56,7 @@ ASTValidation::visit (AST::LoopLabel &label)
 void
 ASTValidation::visit (AST::ConstantItem &const_item)
 {
-  if (!const_item.has_expr () && ctx.peek () != Kind::TRAIT_IMPL)
+  if (!const_item.has_expr () && ctx.peek () != Kind::TRAIT)
     {
       rust_error_at (const_item.get_locus (),
 		     "associated constant in %<impl%> without body");

gcc/testsuite/rust/compile/issue-3541-1.rs

@@ -0,0 +1,5 @@
+impl B for u32 {
+    const BAR: i32; // { dg-error "associated constant in .impl." }
+}
+
+trait B {}

gcc/testsuite/rust/compile/issue-3541-2.rs

@@ -0,0 +1,3 @@
+trait B {
+    const BAR: i32;
+}