buildflag.h - mozsearch

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// 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_