Enable MSVC warning for unused locals.

mojo/public/cpp/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): Maybe rename "MacrosCppTest" -> "MacrosTest" if/when this gets
 // compiled into a different binary from the C API tests.
 // TODO(vtl): Fix no-compile tests (which are all disabled; crbug.com/105388)
@@ skipping 49 matching lines @@
   y.NoOp();
 }
 
 // Test that |MOJO_ARRAYSIZE()| works in a |static_assert()|.
 const int kGlobalArray[5] = {1, 2, 3, 4, 5};
 static_assert(MOJO_ARRAYSIZE(kGlobalArray) == 5u,
               "MOJO_ARRAY_SIZE() failed in static_assert()");
 
 TEST(MacrosCppTest, ArraySize) {
   double local_array[4] = {6.7, 7.8, 8.9, 9.0};
+  MOJO_ALLOW_UNUSED_LOCAL(local_array);

[jamesr, 2014/11/18 00:44:16]

this local seems to be used on the next line - no? is this a toolchain bug?

[Peter Kasting, 2014/11/18 00:50:30]

MSVC considers something unused if e.g. you only ever take sizeof(local), or
refer to it in typedefs, or the like, and not actually use its value.  I find
this arguable, but it turns out to be fairly rare that we actually want to use a
variable for only such purposes and nothing else, so it's easy enough to just
say this is ALLOW_UNUSED and move on.

The total number of places across the codebase that MSVC's quirks cause us to
have to do something otherwise-ugly, like this, is a small subset of the changes
in this CL -- less than half a dozen total -- and the process of enabling this
warning has turned up some questionable code and potential bugs, so I think the
tradeoff is worth it.

   EXPECT_EQ(4u, MOJO_ARRAYSIZE(local_array));
 }
 
 // Note: MSVS is very strict (and arguably buggy) about warnings for classes
 // defined in a local scope, so define these globally.
 class MoveOnlyInt {
   MOJO_MOVE_ONLY_TYPE_FOR_CPP_03(MoveOnlyInt, RValue)
 
  public:
   MoveOnlyInt() : is_set_(false), value_() {}
@@ skipping 36 matching lines @@
   EXPECT_FALSE(y.is_set());
   EXPECT_TRUE(z.is_set());
   EXPECT_EQ(123, z.value());
   z = z.Pass();
   EXPECT_TRUE(z.is_set());
   EXPECT_EQ(123, z.value());
 }
 
 }  // namespace
 }  // namespace mojo