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| 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/build_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_ |
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