Base: First pass at having base.dll: definition of

base/base_api.h

+// 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.
+
+#ifndef BASE_BASE_API_H_
+#define BASE_BASE_API_H_
+#pragma once
+
+#if !defined(BASE_IMPLEMENTATION)
+#define BASE_IMPLEMENTATION 0

[wtc, 2011/03/23 22:05:12]

I think we should not define BASE_IMPLEMENTATION as 0.
We should leave BASE_IMPLEMENTATION undefined, and change
the test on line 14 from
  #if BASE_IMPLEMENTATION
to
  #if defined(BASE_IMPLEMENTATION)

Where do you add -DBASE_IMPLEMENTATION to the compiler
command line?

[rvargas (doing something else), 2011/03/23 22:59:04]

BASE_DLL and BASE_IMPLEMENTATION are defined on the gyp file that generates the
project files, but that is the last step, after everything else is ready.

To be honest, I just copied the pattern used by the equivalent file in
webkit/v8/gurl. I would have also written this without defining BASE_IMPL to 0,
but I see some value in having the exact same pattern that we use in other
places.

+#endif
+
+#if defined(WIN32) && defined(BASE_DLL)

[wtc, 2011/03/23 22:05:12]

Nit: I think we prefer our own OS_WIN macro over WIN32.

[rvargas (doing something else), 2011/03/23 22:59:04]

That's an interesting point, but in order to do that, this file would have to
include base/build_config.h, and that would muddy the waters a bit.

I think it's better to have a very simple header that doesn't depend on any
other header from the module that it's trying to define the interface for. There
is also the point that this whole exercise is Windows-only.

But, I could be convinced about changing the structure of this file :)

+#if BASE_IMPLEMENTATION

[wtc, 2011/03/25 18:17:29]

Thank you for the reply.  I agree base_api.h should not
need to include build_config.h.  So we should only test
compiler-predefined macros or macros defined on the compiler
command line.

I think we should remove lines 9-11 and test
#if defined(BASE_IMPLEMENTATION)
here.  Lines 9-11 seem to show we don't know the
C preprocessor replaces an undefined macro with the
value 0L in a conditional expression.  We can change
WebKit and googleurl if we want consistency.

[brettw, 2011/03/26 18:09:46]

This sounds fine to me.

[rvargas (doing something else), 2011/03/28 18:52:21]

Yeah. A CL with this change is up for review
(http://codereview.chromium.org/6747014/).

+#define BASE_API __declspec(dllexport)
+#else
+#define BASE_API __declspec(dllimport)
+#endif
+#else
+#define BASE_API
+#endif
+
+#endif  // BASE_BASE_API_H_