gccrs: Support looking up super traits for trait items

When supporting calls to super traits we need to allow lookups based on
the super traits as specified on the TraitReferences.

Fixes #1555

gcc/rust/ChangeLog:

	* typecheck/rust-hir-trait-ref.h (lookup_trait_item): Add lookup
	in super_trait.

gcc/testsuite/ChangeLog:

	* rust/compile/torture/issue-1555.rs: New test.

1 files changed, 19 insertions, 0 deletions

diff --git a/gcc/rust/typecheck/rust-hir-trait-ref.h b/gcc/rust/typecheck/rust-hir-trait-ref.h
index f6a3328..7eeb330 100644
--- a/gcc/rust/typecheck/rust-hir-trait-ref.h
+++ b/gcc/rust/typecheck/rust-hir-trait-ref.h
@@ -336,6 +336,15 @@ public:
 	    return true;
 	  }
       }
+
+    // lookup super traits
+    for (const auto &super_trait : super_traits)
+      {
+	bool found = super_trait->lookup_trait_item (ident, ref);
+	if (found)
+	  return true;
+      }
+
     return false;
   }
 
@@ -351,6 +360,16 @@ public:
 	if (ident.compare (item.get_identifier ()) == 0)
 	  return &item;
       }
+
+    // lookup super traits
+    for (const auto &super_trait : super_traits)
+      {
+	const TraitItemReference *res
+	  = super_trait->lookup_trait_item (ident, type);
+	if (!res->is_error ())
+	  return res;
+      }
+
     return &TraitItemReference::error_node ();
   }