Disallow redundant Bind calls.

base/bind_unittest.nc

 // Copyright (c) 2011 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 is a "No Compile Test" suite.
 // http://dev.chromium.org/developers/testing/no-compile-tests
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/macros.h"
@@ skipping 190 matching lines @@
   Closure callback_mismatches_bind_type = Bind(&VoidPolymorphic1<int>);
 }
 
 #elif defined(NCTEST_DISALLOW_CAPTURING_LAMBDA)  // [r"fatal error: implicit instantiation of undefined template 'base::internal::FunctorTraits<\(lambda at ../../base/bind_unittest.nc:[0-9]+:[0-9]+\), void>'"]
 
 void WontCompile() {
   int i = 0;
   Bind([i]() {});
 }
 
+#elif defined(NCTEST_DISALLOW_BINDING_ONCE_CALLBACK_WITH_NO_ARGS)  // [r"static_assert failed \"Attempting to bind a base::Callback with no additional arguments: save a heap allocation and use the original base::Callback\""]
+
+void WontCompile() {
+  internal::OnceClosure cb = internal::BindOnce([] {});
+  internal::OnceClosure cb2 = internal::BindOnce(cb);

[dcheng, 2016/09/24 00:49:17]

This technically fails for two reasons: cb is not copyable (we should use
std::move) and the static_assert.

Since the nocompile driver doesn't know where to find the libc++ headers, I
could add a rvalue static cast here if anyone feels strongly about tying it to
only one error.

This has the nice property of verifying that you get two errors for the price of
one though? So maybe we can just keep this way?

[dcheng, 2016/09/24 00:52:55]

Actually, I had a typo the first time. Updated this to just use std::move() and
verify the nocompile test still passes (e.g. compilation fails)

+}
+
+#elif defined(NCTEST_DISALLOW_BINDING_REPEATING_CALLBACK_WITH_NO_ARGS)  // [r"static_assert failed \"Attempting to bind a base::Callback with no additional arguments: save a heap allocation and use the original base::Callback\""]
+
+void WontCompile() {
+  Closure cb = Bind([] {});
+  Closure cb2 = Bind(cb);
+}
+
 #endif
 
 }  // namespace base