Traverse function return attributes.

The dependency graph needs to traverse function return attributes
as they can contain expressions now.

Bug: chromium:1377630
Change-Id: I338aa7ff1105baed93871ec44ca02285fabf407d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/106845
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/resolver/dependency_graph.cc

diff --git a/src/tint/resolver/dependency_graph.cc b/src/tint/resolver/dependency_graph.cc
index b6001c1..5a21c55 100644
--- a/src/tint/resolver/dependency_graph.cc
+++ b/src/tint/resolver/dependency_graph.cc
@@ -194,6 +194,7 @@
             [&](const ast::Function* func) {
                 Declare(func->symbol, func);
                 TraverseAttributes(func->attributes);
+                TraverseAttributes(func->return_type_attributes);
                 TraverseFunction(func);
             },
             [&](const ast::Variable* var) {

src/tint/resolver/dependency_graph_test.cc

diff --git a/src/tint/resolver/dependency_graph_test.cc b/src/tint/resolver/dependency_graph_test.cc
index ae314b8..311c9cc 100644
--- a/src/tint/resolver/dependency_graph_test.cc
+++ b/src/tint/resolver/dependency_graph_test.cc
@@ -1270,7 +1270,9 @@
              Return(V),                                 //
              Break(),                                   //
              Discard(),                                 //
-         });                                            //
+         },
+         utils::Empty,                 // function attributes
+         utils::Vector{Location(V)});  // return attributes
     // Exercise type traversal
     GlobalVar(Sym(), ty.atomic(T));
     GlobalVar(Sym(), ty.bool_());