Mojo: Require our public options structs to be aligned like int64_t's.

mojo/public/c/system/tests/macros_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file tests the C Mojo system macros and consists of "positive" tests,
 // i.e., those verifying that things work (without compile errors, or even
 // warnings if warnings are treated as errors).
 // TODO(vtl): Fix no-compile tests (which are all disabled; crbug.com/105388)
 // and write some "negative" tests.
 
@@ skipping 26 matching lines @@
 // First test |MOJO_COMPILE_ASSERT()| in a global scope.
 MOJO_COMPILE_ASSERT(sizeof(int64_t) == 2 * sizeof(int32_t),
                     bad_compile_assert_failure_in_global_scope);
 
 TEST(MacrosTest, CompileAssert) {
   // Then in a local scope.
   MOJO_COMPILE_ASSERT(sizeof(int32_t) == 2 * sizeof(int16_t),
                       bad_compile_assert_failure);
 }
 
+TEST(MacrosTest, Alignof) {
+  // Strictly speaking, this isn't a portable test, but I think it'll pass on
+  // all the platforms we currently support.
+  EXPECT_EQ(1u, MOJO_ALIGNOF(char));
+  EXPECT_EQ(4u, MOJO_ALIGNOF(int32_t));
+  EXPECT_EQ(8u, MOJO_ALIGNOF(int64_t));
+  EXPECT_EQ(8u, MOJO_ALIGNOF(double));
+}
+
+// These structs are used in the Alignas test. Define them globally to avoid
+// MSVS warnings/errors.
+#if defined(_MSC_VER)
+#pragma warning(push)
+// Disable the warning "structure was padded due to __declspec(align())".
+#pragma warning(disable:4324)
+#endif
+struct MOJO_ALIGNAS(1) StructAlignas1 { char x; };
+struct MOJO_ALIGNAS(4) StructAlignas4 { char x; };
+struct MOJO_ALIGNAS(8) StructAlignas8 { char x; };
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
+
+TEST(MacrosTest, Alignas) {
+  EXPECT_EQ(1u, MOJO_ALIGNOF(StructAlignas1));
+  EXPECT_EQ(4u, MOJO_ALIGNOF(StructAlignas4));
+  EXPECT_EQ(8u, MOJO_ALIGNOF(StructAlignas8));
+}
+
 }  // namespace
 }  // namespace mojo