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.

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 ();
   }
 

gcc/testsuite/rust/compile/torture/issue-1555.rs

@@ -0,0 +1,48 @@
+extern "C" {
+    fn printf(s: *const i8, ...);
+}
+
+struct Foo(i32);
+trait Bar {
+    fn baz(&self);
+}
+
+trait Baz: Bar {
+    fn qux(&self);
+}
+
+impl Bar for Foo {
+    fn baz(&self) {
+        unsafe {
+            let a = "baz %i\n\0";
+            let b = a as *const str;
+            let c = b as *const i8;
+
+            printf(c, self.0);
+        }
+    }
+}
+
+impl Baz for Foo {
+    fn qux(&self) {
+        unsafe {
+            let a = "qux %i\n\0";
+            let b = a as *const str;
+            let c = b as *const i8;
+
+            printf(c, self.0);
+        }
+    }
+}
+
+fn static_dispatch<T: Baz>(t: &T) {
+    t.baz();
+    t.qux();
+}
+
+pub fn main() {
+    let a;
+    a = &Foo(123);
+
+    static_dispatch(a);
+}