gccrs: Fix ICE by adding check for enum candidate's in TypePath resolution

Fixes #2479

gcc/rust/ChangeLog:

	* typecheck/rust-hir-trait-resolve.cc (TraitItemReference::resolve_item):
	always resolve the type even when its an a mandatory trait item
	* typecheck/rust-hir-type-check-type.cc (TypeCheckType::resolve_root_path):
	Add check for enum candidates otherwise you get undefined behaviour

gcc/testsuite/ChangeLog:

	* rust/compile/issue-2479.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

gcc/rust/typecheck/rust-hir-trait-resolve.cc

@@ -339,13 +339,13 @@ TraitItemReference::resolve_item (HIR::TraitItemConst &constant)
 void
 TraitItemReference::resolve_item (HIR::TraitItemFunc &func)
 {
-  if (!is_optional ())
-    return;
-
   TyTy::BaseType *item_tyty = get_tyty ();
   if (item_tyty->get_kind () == TyTy::TypeKind::ERROR)
     return;
 
+  if (!is_optional ())
+    return;
+
   // check the block and return types
   rust_assert (item_tyty->get_kind () == TyTy::TypeKind::FNDEF);
 

gcc/rust/typecheck/rust-hir-type-check-type.cc

@@ -440,6 +440,16 @@ TypeCheckType::resolve_root_path (HIR::TypePath &path, size_t *offset,
       *root_resolved_node_id = ref_node_id;
       *offset = *offset + 1;
       root_tyty = lookup;
+
+      // this enforces the proper get_segments checks to take place
+      bool is_adt = root_tyty->get_kind () == TyTy::TypeKind::ADT;
+      if (is_adt)
+	{
+	  const TyTy::ADTType &adt
+	    = *static_cast<const TyTy::ADTType *> (root_tyty);
+	  if (adt.is_enum ())
+	    return root_tyty;
+	}
     }
 
   return root_tyty;
@@ -498,6 +508,14 @@ TypeCheckType::resolve_segments (
       prev_segment = tyseg;
       tyseg = candidate.ty;
 
+      if (candidate.is_enum_candidate ())
+	{
+	  rust_error_at (seg->get_locus (),
+			 "expected type, found variant of %s",
+			 tyseg->get_name ().c_str ());
+	  return new TyTy::ErrorType (expr_id);
+	}
+
       if (candidate.is_impl_candidate ())
 	{
 	  resolved_node_id

gcc/testsuite/rust/compile/issue-2479.rs

@@ -0,0 +1,22 @@
+#![allow(unused)]
+fn main() {
+enum Dragon {
+    Born,
+}
+
+fn oblivion() -> Dragon::Born {
+// { dg-error "expected type, found variant of Dragon" "" { target *-*-* } .-1 }
+// { dg-error "failed to resolve return type" "" { target *-*-* } .-2 }
+    Dragon::Born
+}
+
+enum Wizard {
+    Gandalf,
+    Saruman,
+}
+
+trait Isengard {
+    fn wizard(_: Wizard::Saruman);
+    // { dg-error "expected type, found variant of Wizard" "" { target *-*-* } .-1 }
+}
+}