Support gmock matchers in mojo StructPtr

gmock's Pointee matcher dereferences raw or smart pointers. It depends
on smart pointers defining element_type to recognize what type they
hold. This patch adds element_type to StructPtr and InlineStructPtr so
gmock will recognize them as smart pointers.

R=rockot

Change-Id: I06333a31c0a958fd24784e1ee2244d0232267bba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2403583
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Joe Mason <joenotcharles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805915}

mojo/public/cpp/bindings/struct_ptr.h

@@ -35,6 +35,10 @@ class StructPtr {
  public:
   using Struct = S;
 
+  // Exposing StructPtr<S>::element_type allows gmock's Pointee matcher to
+  // dereference StructPtr's.
+  using element_type = S;
+
   StructPtr() = default;
   StructPtr(std::nullptr_t) {}
 
@@ -122,6 +126,10 @@ class InlinedStructPtr {
  public:
   using Struct = S;
 
+  // Exposing InlinedStructPtr<S>::element_type allows gmock's Pointee matcher
+  // to dereference InlinedStructPtr's.
+  using element_type = S;
+
   InlinedStructPtr() = default;
   InlinedStructPtr(std::nullptr_t) {}
 

mojo/public/cpp/bindings/tests/struct_unittest.cc

@@ -11,6 +11,7 @@
 #include "mojo/public/cpp/system/message_pipe.h"
 #include "mojo/public/interfaces/bindings/tests/test_export2.mojom.h"
 #include "mojo/public/interfaces/bindings/tests/test_structs.mojom.h"
+#include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace mojo {
@@ -542,5 +543,24 @@ TEST_F(StructTest, EnumNestedStructTest) {
   EXPECT_EQ(EnumNestedStruct::StructEnum::SECOND, output->local_enum_state_);
 }
 
+TEST_F(StructTest, Matcher) {
+  // Pointee will dereference StructPtr<S> or InlinedStructPtr<S> to get S.
+  // This test ensures that the matcher compiles and works.
+  using ::testing::Pointee;
+
+  using ::testing::AllOf;
+  using ::testing::Field;
+
+  mojo::InlinedStructPtr<Rect> rect = MakeRect();
+  EXPECT_THAT(
+      rect, Pointee(AllOf(Field(&Rect::x, 1), Field(&Rect::y, 2),
+                          Field(&Rect::width, 10), Field(&Rect::height, 20))));
+
+  mojo::StructPtr<MultiVersionStruct> multi = MakeMultiVersionStruct();
+  EXPECT_THAT(multi, Pointee(AllOf(Field(&MultiVersionStruct::f_int32, 123),
+                                   Field(&MultiVersionStruct::f_rect,
+                                         Pointee(Field(&Rect::x, 5))))));
+}
+
 }  // namespace test
 }  // namespace mojo