| # Copyright 2015 The Chromium Authors |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| # Generates a header with preprocessor defines specified by the build file. |
| # |
| # The flags are converted to function-style defines with mangled names and |
| # code uses an accessor macro to access the values. This is to try to |
| # minimize bugs where code checks whether something is defined or not, and |
| # the proper header isn't included, meaning the answer will always be silently |
| # false or might vary across the code base. |
| # |
| # In the GN template, specify build flags in the template as a list |
| # of strings that encode key/value pairs like this: |
| # |
| # flags = [ "ENABLE_FOO=1", "ENABLE_BAR=$enable_bar" ] |
| # |
| # The GN values "true" and "false" will be mapped to 0 and 1 for boolean |
| # #if flags to be expressed naturally. This means you can't directly make a |
| # define that generates C++ value of true or false for use in code. If you |
| # REALLY need this, you can also use the string "(true)" and "(false)" to |
| # prevent the rewriting. |
| |
| # To check the value of the flag in C code: |
| # |
| # #include "path/to/here/header_file.h" |
| # |
| # #if BUILDFLAG(ENABLE_FOO) |
| # ... |
| # #endif |
| # |
| # const char kSpamServerUrl[] = BUILDFLAG(SPAM_SERVER_URL); |
| # |
| # There will be no #define called ENABLE_FOO so if you accidentally test for |
| # that in an ifdef it will always be negative. |
| # |
| # |
| # Template parameters |
| # |
| # flags [required, list of strings] |
| # Flag values as described above. |
| # |
| # header [required, string] |
| # File name for generated header. By default, this will go in the |
| # generated file directory for this target, and you would include it |
| # with: |
| # #include "<path_to_this_BUILD_file>/<header>" |
| # |
| # header_dir [optional, string] |
| # Override the default location of the generated header. The string will |
| # be treated as a subdirectory of the root_gen_dir. For example: |
| # header_dir = "foo/bar" |
| # Then you can include the header as: |
| # #include "foo/bar/baz.h" |
| # |
| # deps, public_deps, testonly, visibility |
| # Normal meaning. |
| # |
| # |
| # Grit defines |
| # |
| # If one .grd file uses a flag, just add to the grit target: |
| # |
| # defines = [ |
| # "enable_doom_melon=$enable_doom_melon", |
| # ] |
| # |
| # If multiple .grd files use it, you'll want to put the defines in a .gni file |
| # so it can be shared. Generally this .gni file should include all grit defines |
| # for a given module (for some definition of "module"). Then do: |
| # |
| # defines = ui_grit_defines |
| # |
| # If you forget to do this, the flag will be implicitly false in the .grd file |
| # and those resources won't be compiled. You'll know because the resource |
| # #define won't be generated and any code that uses it won't compile. If you |
| # see a missing IDS_* string, this is probably the reason. |
| # |
| # |
| # Example |
| # |
| # buildflag_header("foo_buildflags") { |
| # header = "foo_buildflags.h" |
| # |
| # flags = [ |
| # # This uses the GN build flag enable_doom_melon as the definition. |
| # "ENABLE_DOOM_MELON=$enable_doom_melon", |
| # |
| # # This force-enables the flag. |
| # "ENABLE_SPACE_LASER=true", |
| # |
| # # This will expand to the quoted C string when used in source code. |
| # "SPAM_SERVER_URL=\"http://www.example.com/\"", |
| # ] |
| # } |
| template("buildflag_header") { |
| action(target_name) { |
| script = "//build/write_buildflag_header.py" |
| |
| if (defined(invoker.header_dir)) { |
| header_file = "${invoker.header_dir}/${invoker.header}" |
| } else { |
| # Compute the path from the root to this file. |
| header_file = rebase_path(".", "//") + "/${invoker.header}" |
| } |
| |
| outputs = [ "$root_gen_dir/$header_file" ] |
| |
| # Always write --flags to the file so it's not empty. Empty will confuse GN |
| # into thinking the response file isn't used. |
| response_file_contents = [ "--flags" ] |
| if (defined(invoker.flags)) { |
| response_file_contents += invoker.flags |
| } |
| |
| args = [ |
| "--output", |
| header_file, # Not rebased, Python script puts it inside gen-dir. |
| "--rulename", |
| get_label_info(":$target_name", "label_no_toolchain"), |
| "--gen-dir", |
| rebase_path(root_gen_dir, root_build_dir), |
| "--definitions", |
| "{{response_file_name}}", |
| ] |
| |
| forward_variables_from(invoker, |
| [ |
| "deps", |
| "public_deps", |
| "testonly", |
| "visibility", |
| ]) |
| |
| public_deps = [ "//build:buildflag_header_h" ] |
| } |
| } |