| // Copyright 2015 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_BUILDFLAG_H_ |
| #define BUILD_BUILDFLAG_H_ |
| |
| // These macros un-mangle the names of the build flags in a way that looks |
| // natural, and gives errors if the flag is not defined. Normally in the |
| // preprocessor it's easy to make mistakes that interpret "you haven't done |
| // the setup to know what the flag is" as "flag is off". Normally you would |
| // include the generated header rather than include this file directly. |
| // |
| // This is for use with generated headers. See build/buildflag_header.gni. |
| |
| // This dance of two macros does a concatenation of two preprocessor args using |
| // ## doubly indirectly because using ## directly prevents macros in that |
| // parameter from being expanded. |
| #define BUILDFLAG_CAT_INDIRECT(a, b) a ## b |
| #define BUILDFLAG_CAT(a, b) BUILDFLAG_CAT_INDIRECT(a, b) |
| |
| // Accessor for build flags. |
| // |
| // To test for a value, if the build file specifies: |
| // |
| // ENABLE_FOO=true |
| // |
| // Then you would check at build-time in source code with: |
| // |
| // #include "foo_flags.h" // The header the build file specified. |
| // |
| // #if BUILDFLAG(ENABLE_FOO) |
| // ... |
| // #endif |
| // |
| // There will no #define called ENABLE_FOO so if you accidentally test for |
| // whether that is defined, it will always be negative. You can also use |
| // the value in expressions: |
| // |
| // const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME); |
| // |
| // Because the flag is accessed as a preprocessor macro with (), an error |
| // will be thrown if the proper header defining the internal flag value has |
| // not been included. |
| #define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)()) |
| |
| #endif // BUILD_BUILDFLAG_H_ |