Linux: use generated library loader for gsettings.

build/linux/gsettings.h

+// Copyright (c) 2012 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 BUILD_LINUX_GSETTINGS_H_
+#define BUILD_LINUX_GSETTINGS_H_
+
+#include <gio/gio.h>
+
+// We replicate the prototypes for the g_settings APIs we need. We may not
+// even be compiling on a system that has them.
+// TODO(phajdan.jr): This will no longer be needed after switch to Precise,
+// see http://crbug.com/158577 .

[Ryan Sleevi, 2012/11/29 21:51:04]

nit: Can you rewrite this comment to provide clearer context about what's going
on here.

// The GSettings API was not part of GIO until GIO version XXX, while platform
YYY ships with version VVV.
// To allow compiling on platform YYY when using dlopen() to determine
// if GSettings is available, forward declarations are provided.
//
// If compiling with version XXX, these won't conflict, because
// they're identical to the types defined.

[Paweł Hajdan Jr., 2012/11/29 22:29:00]

Done.

+struct _GSettings;
+typedef struct _GSettings GSettings;

[Ryan Sleevi, 2012/11/29 21:51:04]

I don't think this will work.

In the original code, it worked because of **name scoping**. That is, the
symbols were part of proxy_config_service_linux's naming scope, and thus did not
conflict with the global symbols from gio.h. If you attempt to compile with
version XXX (on Precise?), you will probably end up with an ODR violation
because the typedef already exists.

[Paweł Hajdan Jr., 2012/11/29 22:29:00]

Green trybot compiles contradict your comment. It works.

[Ryan Sleevi, 2012/11/29 23:02:58]

C forbids this. C++ allows this. You're getting lucky.

+GSettings* g_settings_new(const gchar* schema);
+GSettings* g_settings_get_child(GSettings* settings, const gchar* name);
+gboolean g_settings_get_boolean(GSettings* settings, const gchar* key);
+gchar* g_settings_get_string(GSettings* settings, const gchar* key);
+gint g_settings_get_int(GSettings* settings, const gchar* key);
+gchar** g_settings_get_strv(GSettings* settings, const gchar* key);
+const gchar* const* g_settings_list_schemas();

[Ryan Sleevi, 2012/11/29 21:51:04]

In the existing code, these forward declarations were only used when
DLOPEN_GSETTINGS was defined. This ensured that it would be a *compile* failure
if you attempted to compile while using version VVV and did not also use dlopen.

With this change you have made, it will be a *link* failure, which is much less
desirable and arguably more subtle.

[Paweł Hajdan Jr., 2012/11/29 22:29:00]

Nope, when linking directly system header will be used. In other words, I know
what I'm doing.

This is yet another reason this generator is cool. :)

+
+#endif  // BUILD_LINUX_GSETTINGS_H_