| Ben Murdoch | 097c5b2 | 2016-05-18 11:27:45 +0100 | [diff] [blame] | 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_ |