1// Copyright 2015 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef BUILD_BUILDFLAG_H_
6#define BUILD_BUILDFLAG_H_
7
8// These macros un-mangle the names of the build flags in a way that looks
9// natural, and gives errors if the flag is not defined. Normally in the
10// preprocessor it's easy to make mistakes that interpret "you haven't done
11// the setup to know what the flag is" as "flag is off". Normally you would
12// include the generated header rather than include this file directly.
13//
14// This is for use with generated headers. See build/buildflag_header.gni.
15
16// This dance of two macros does a concatenation of two preprocessor args using
17// ## doubly indirectly because using ## directly prevents macros in that
18// parameter from being expanded.
19#define BUILDFLAG_CAT_INDIRECT(a, b) a ## b
20#define BUILDFLAG_CAT(a, b) BUILDFLAG_CAT_INDIRECT(a, b)
21
22// Accessor for build flags.
23//
24// To test for a value, if the build file specifies:
25//
26//   ENABLE_FOO=true
27//
28// Then you would check at build-time in source code with:
29//
30//   #include "foo_flags.h"  // The header the build file specified.
31//
32//   #if BUILDFLAG(ENABLE_FOO)
33//     ...
34//   #endif
35//
36// There will no #define called ENABLE_FOO so if you accidentally test for
37// whether that is defined, it will always be negative. You can also use
38// the value in expressions:
39//
40//   const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME);
41//
42// Because the flag is accessed as a preprocessor macro with (), an error
43// will be thrown if the proper header defining the internal flag value has
44// not been included.
45#define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)())
46
47#endif  // BUILD_BUILDFLAG_H_
48