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