Java Flag Generator

Generates a Java class with typed accessors for the features that a C++ feature list exposes to Java through kFeaturesExposedToJava.

For each &namespace::kFoo in the array, the generated class contains:

/** {@code ns::kFoo} */
public static final class Foo {
    public static final String NAME = "FooFeatureName";

    public static boolean isEnabled() {
        return isFeatureEnabled(NAME);
    }
}

NAME is the feature name string from the feature's definition (BASE_FEATURE(kFoo, "FooFeatureName", ...)), not a name derived from the identifier.

Usage

import("//base/android/java_flag_generator/java_flag_generator.gni")

java_flag_generator("java_flags") {
  sources = [ "android/chrome_feature_list.cc" ]
  class_name = "org.chromium.chrome.browser.flags.ChromeFeatures"
}

android_library("java") {
  srcjar_deps = [ ":java_flags" ]
  ...
}

List the target in the srcjar_deps of exactly one android_library(); others should depend on that library.

Variables

• sources: C++ files that define kFeaturesExposedToJava.
• class_name: Fully-qualified name of the generated class.
• feature_map_class_name (optional): FeatureMap subclass used by all sources. By default, each source's map is derived from its JNI_<Name>_GetNativeMap function and assumed to be in the package of class_name.
• deps (optional): Must include the targets that generate any generated FEATURE_DEFINITION_FILEs.

With a single FeatureMap, the generated helper is isFeatureEnabled(). With several (multiple sources backed by different maps), there is one helper per map, named isFeatureEnabledIn<FeatureMapName>().

Finding feature definitions

For each feature in kFeaturesExposedToJava, the generator looks for feature definitions in:

1. The source itself.
2. For each quoted #include "path/foo.h", the file path/foo.cc. The path is tried relative to the source root, then relative to the including file.
3. Files listed in FEATURE_DEFINITION_FILE directives.

If a feature‘s definition can’t be found, the build fails. Fix it by adding a directive to the source naming the file that defines the feature:

// FEATURE_DEFINITION_FILE: //third_party/blink/common/features.cc

Directive paths are looked up in the source tree first, then in $root_gen_dir. For a generated file, add the target that generates it to deps.

Directives that are not needed (the file is already found automatically, or no feature uses it) are errors, so the list stays accurate.

What counts as a definition

Any ALL_CAPS macro call whose name contains FEATURE (but not DECLARE or PARAM) and whose first argument is a kCamelCase identifier, e.g. BASE_FEATURE(...) or BASE_FEATURE_WITH_COUNTRY_RESTRICTIONS(...). For BASE_FEATURE and BASE_RUNTIME_MUTABLE_FEATURE, the feature name is the second argument when it is a string literal; otherwise the feature name is derived from the identifier (kFoo -> "Foo").