[Impeller] Make glIsTexture mockable for use by the ReactorGLES.NameUntrackedHandle test (#162082)

ReactorGLES.NameUntrackedHandle calls SetDebugLabel, which invokes
glIsTexture. glIsTexture should return a GLboolean. But the mock GLES
resolver was mapping glIsTexture to a no-op function with a void return
type.

This change makes glIsTexture mockable so the test can ensure that it
returns the appropriate result.

engine/src/flutter/impeller/renderer/backend/gles/test/mock_gles.cc

@@ -39,13 +39,23 @@ auto const kExtensions = std::vector<const char*>{
 };
 
 namespace {
+
+template <typename T>
+struct function_traits;
+
+template <typename C, typename Ret, typename... Args>
+struct function_traits<Ret (C::*)(Args...)> {
+  using return_type = Ret;
+};
+
 template <typename Func, typename... Args>
-void CallMockMethod(Func func, Args&&... args) {
+auto CallMockMethod(Func func, Args&&... args) {
   if (auto mock_gles = g_mock_gles.lock()) {
     if (mock_gles->GetImpl()) {
-      (mock_gles->GetImpl()->*func)(std::forward<Args>(args)...);
+      return (mock_gles->GetImpl()->*func)(std::forward<Args>(args)...);
     }
   }
+  return typename function_traits<Func>::return_type();
 }
 }  // namespace
 
@@ -194,6 +204,13 @@ void mockObjectLabelKHR(GLenum identifier,
 static_assert(CheckSameSignature<decltype(mockObjectLabelKHR),  //
                                  decltype(glObjectLabelKHR)>::value);
 
+GLboolean mockIsTexture(GLuint texture) {
+  return CallMockMethod(&IMockGLESImpl::IsTexture, texture);
+}
+
+static_assert(CheckSameSignature<decltype(mockGenTextures),  //
+                                 decltype(glGenTextures)>::value);
+
 // static
 std::shared_ptr<MockGLES> MockGLES::Init(
     std::unique_ptr<MockGLESImpl> impl,
@@ -257,6 +274,8 @@ const ProcTableGLES::Resolver kMockResolverGLES = [](const char* name) {
     return reinterpret_cast<void*>(mockObjectLabelKHR);
   } else if (strcmp(name, "glGenBuffers") == 0) {
     return reinterpret_cast<void*>(mockGenBuffers);
+  } else if (strcmp(name, "glIsTexture") == 0) {
+    return reinterpret_cast<void*>(mockIsTexture);
   } else {
     return reinterpret_cast<void*>(&doNothing);
   }

engine/src/flutter/impeller/renderer/backend/gles/test/mock_gles.h

@@ -36,6 +36,7 @@ class IMockGLESImpl {
                                       GLuint64* result) {}
   virtual void DeleteQueriesEXT(GLsizei size, const GLuint* queries) {}
   virtual void GenBuffers(GLsizei n, GLuint* buffers) {}
+  virtual GLboolean IsTexture(GLuint texture) { return true; }
 };
 
 class MockGLESImpl : public IMockGLESImpl {
@@ -70,6 +71,7 @@ class MockGLESImpl : public IMockGLESImpl {
               (GLsizei size, const GLuint* queries),
               (override));
   MOCK_METHOD(void, GenBuffers, (GLsizei n, GLuint* buffers), (override));
+  MOCK_METHOD(GLboolean, IsTexture, (GLuint texture), (override));
 };
 
 /// @brief      Provides a mocked version of the |ProcTableGLES| class.

engine/src/flutter/impeller/renderer/backend/gles/test/reactor_unittests.cc

@@ -17,6 +17,7 @@ namespace impeller {
 namespace testing {
 
 using ::testing::_;
+using ::testing::NiceMock;
 
 class TestWorker : public ReactorGLES::Worker {
  public:
@@ -96,13 +97,14 @@ TEST(ReactorGLES, UntrackedHandle) {
 }
 
 TEST(ReactorGLES, NameUntrackedHandle) {
-  auto mock_gles_impl = std::make_unique<MockGLESImpl>();
+  auto mock_gles_impl = std::make_unique<NiceMock<MockGLESImpl>>();
 
   EXPECT_CALL(*mock_gles_impl, GenTextures(1, _))
       .WillOnce([](GLsizei size, GLuint* queries) { queries[0] = 1234; });
   EXPECT_CALL(*mock_gles_impl,
               ObjectLabelKHR(_, 1234, _, ::testing::StrEq("hello, joe!")))
       .Times(1);
+  ON_CALL(*mock_gles_impl, IsTexture).WillByDefault(::testing::Return(GL_TRUE));
 
   std::shared_ptr<MockGLES> mock_gles =
       MockGLES::Init(std::move(mock_gles_impl));