Add Java side of JNI annotation processor for static methods

First iteration of the JNI annotation processor for static methods.

Adds a new annotation @JNIStaticNatives that when used
on an inner interface, will trigger the annotation processor
to generate native declarations and a wrapper class.

I provided a sample usage in
example/jni_generator/SampleForAnnotationProcessor.java

Change-Id: If888b6fd41eafccb54af32aebde3a850bab55849
Reviewed-on: https://chromium-review.googlesource.com/c/1239348
Commit-Queue: Aiden Benner <abenner@google.com>
Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597359}

base/BUILD.gn

@@ -2872,6 +2872,13 @@ if (is_android) {
     classes = [ "java/lang/Runtime.class" ]
   }
 
+  java_library("jni_processor_annotations_java") {
+    supports_android = true
+    java_files = [
+      "android/java/src/org/chromium/base/annotations/JniStaticNatives.java",
+    ]
+  }
+
   android_library("base_java") {
     srcjar_deps = [
       ":base_android_java_enums_srcjar",

base/android/java/src/org/chromium/base/annotations/JniStaticNatives.java

+// Copyright 2018 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.
+package org.chromium.base.annotations;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.SOURCE)
+public @interface JniStaticNatives {}

base/android/jni_generator/BUILD.gn

@@ -21,6 +21,14 @@ android_library("jni_sample_java") {
   ]
 }
 
+android_library("jni_annotation_sample_java") {
+  java_files = [ "java/src/org/chromium/example/jni_generator/SampleForAnnotationProcessor.java" ]
+  deps = [
+    "//base:jni_processor_annotations_java",
+  ]
+  annotation_processor_deps = [ "//base/android/jni_generator:jni_processor" ]
+}
+
 source_set("jni_sample_native_side") {
   deps = [
     ":jni_sample_header",
@@ -63,6 +71,22 @@ generate_jni_registration("sample_jni_registration") {
 # Serves to test that generated bindings compile properly.
 group("jni_generator_tests") {
   deps = [
+    ":jni_annotation_sample_java",
     ":sample_jni_apk",
   ]
 }
+
+java_annotation_processor("jni_processor") {
+  java_files = [ "java/src/org/chromium/jni_generator/JniProcessor.java" ]
+
+  main_class = "org.chromium.jni_generator.JniProcessor"
+
+  annotation_processor_deps = [ "//third_party/auto:auto_service_processor" ]
+
+  deps = [
+    "//base:jni_processor_annotations_java",
+    "//third_party/android_deps:com_squareup_javapoet_java",
+    "//third_party/auto:auto_service_java",
+    "//third_party/guava:guava_java",
+  ]
+}

base/android/jni_generator/java/src/org/chromium/example/jni_generator/SampleForAnnotationProcessor.java

+// Copyright 2018 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.
+
+package org.chromium.example.jni_generator;
+
+import org.chromium.base.annotations.JniStaticNatives;
+
+/**
+ * Sample class that uses the JNI annotation processor for static methods.
+ * See generated files at bottom.
+ */
+class SampleForAnnotationProcessor {
+    /**
+     * Static methods declared here, each of these refer to a native method
+     * which will have its declaration generated by our annotation processor.
+     * There will also be a class generated to wrap these native methods
+     * with the name SampleForAnnotationProcessorJni which will implement
+     * Natives.
+     */
+    @JniStaticNatives
+    interface Natives {
+        void foo(String a, int b, char c, int[] d);
+        SampleForAnnotationProcessor bar(SampleForAnnotationProcessor sample);
+        String revString(String stringToReverse);
+        String[] sendToNative(String[] strs);
+        SampleForAnnotationProcessor[] sendSamplesToNative(SampleForAnnotationProcessor[] strs);
+        boolean hasPhalange();
+    }
+
+    void test() {
+        int[] x = new int[] {1, 2, 3, 4, 5};
+        String[] strs = new String[] {"the", "quick", "brown", "fox"};
+        strs = SampleForAnnotationProcessorJni.get().sendToNative(strs);
+
+        SampleForAnnotationProcessor[] samples =
+                new SampleForAnnotationProcessor[] {this, this, this};
+        samples = SampleForAnnotationProcessorJni.get().sendSamplesToNative(samples);
+
+        // Instance of Natives accessed through (classname + "Jni").get().
+        SampleForAnnotationProcessorJni.get().foo("Test", 5, 'c', x);
+        SampleForAnnotationProcessor sample = SampleForAnnotationProcessorJni.get().bar(this);
+        boolean hasPhalange = SampleForAnnotationProcessorJni.get().hasPhalange();
+        String s = SampleForAnnotationProcessorJni.get().revString("abcd");
+    }
+}

build/android/gradle/generate_gradle.py

@@ -59,7 +59,8 @@ _DEFAULT_TARGETS = [
     '//chrome/android:chrome_sync_shell_test_apk',
     '//content/public/android:content_junit_tests',
     '//content/shell/android:content_shell_apk',
-    # Needed even with --all since it's a library.
+    # Below must be included even with --all since they are libraries.
+    '//base/android/jni_generator:jni_processor',
     '//tools/android/errorprone_plugin:errorprone_plugin_java',
 ]
 
@@ -952,10 +953,10 @@ def main():
     data = _GenerateGradleFile(
         entry, generator, build_vars, source_properties, jinja_processor)
     if data and not args.all:
-        project_entries.append((entry.ProjectName(), entry.GradleSubdir()))
-        _WriteFile(
-            os.path.join(generator.EntryOutputDir(entry), _GRADLE_BUILD_FILE),
-            data)
+      project_entries.append((entry.ProjectName(), entry.GradleSubdir()))
+      _WriteFile(
+          os.path.join(generator.EntryOutputDir(entry), _GRADLE_BUILD_FILE),
+          data)
   if args.all:
     project_entries.append((_MODULE_ALL, _MODULE_ALL))
     _GenerateModuleAll(

third_party/guava/BUILD.gn

@@ -24,6 +24,10 @@ java_prebuilt("guava_java") {
   visibility = [
     "//third_party/auto:*",
     "//third_party/robolectric:*",
+
+    # jni_processor is a build tool even though it's in base.
+    "//base/android/jni_generator:jni_processor",
+    "//base/android/jni_generator:jni_processor__compile_java",
   ]
   jar_path = "lib/guava.jar"
 }