Refactor Volley into a multi-module project. (#418)

This splits the library into three Gradle modules:

- core - volley core + toolbox
- cronet - CronetHttpStack
- testing - common testing code

The primary purpose is to split out CronetHttpStack into its own Maven
artifact, com.android.volley:volley-cronet, to prevent applications
which aren't using it from having to either suppress Proguard/D8
warnings or pull in the unnecessary dependency.

The testing module is needed to share TestRequest between unit tests
in both core and cronet. It is not published to Maven.

This PR also removes support for the build.gradle/rules.gradle split
which allowed Gradle projects to depend on Volley by source and
specify their own SDK settings. This is no longer worth supporting,
and any client that wishes to depend on Volley via Gradle should do
so via published Maven artifacts instead.

See #412

build.gradle

@@ -1,76 +1,72 @@
-// NOTE: The only changes that belong in this file are the definitions
-// of tool versions (gradle plugin, compile SDK, build tools), so that
-// Volley can be built via gradle as a standalone project.
-//
-// Any other changes to the build config belong in rules.gradle, which
-// is used by projects that depend on Volley but define their own
-// tools versions across all dependencies to ensure a consistent build.
-//
-// Most users should just add this line to settings.gradle:
-//     include(":volley")
-//
-// If you have a more complicated Gradle setup you can choose to use
-// this instead:
-//     include(":volley")
-//     project(':volley').buildFileName = 'rules.gradle'
-
-import net.ltgt.gradle.errorprone.CheckSeverity
-
 buildscript {
     repositories {
+        gradlePluginPortal()
         jcenter()
         google()
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:3.2.1'
+        classpath 'gradle.plugin.com.github.sherter.google-java-format:google-java-format-gradle-plugin:0.6'
+        // NOTE: 0.7 or newer will require upgrading to a newer Android gradle plugin:
+        // https://github.com/tbroyer/gradle-errorprone-plugin/commit/65b1026ebeae1b7ed8c28578c7f6eea512c16bea
+        classpath 'net.ltgt.errorprone:net.ltgt.errorprone.gradle.plugin:0.6.1'
     }
 }
 
-plugins {
-    id "com.github.sherter.google-java-format" version "0.6"
-    // NOTE: 0.7 or newer will require upgrading to a newer Android gradle plugin:
-    // https://github.com/tbroyer/gradle-errorprone-plugin/commit/65b1026ebeae1b7ed8c28578c7f6eea512c16bea
-    id "net.ltgt.errorprone" version "0.6.1"
+allprojects {
+    repositories {
+        jcenter()
+        google()
+    }
 }
 
-googleJavaFormat {
-    toolVersion = '1.5'
-    options style: 'AOSP'
-}
+subprojects {
+    apply plugin: 'com.github.sherter.google-java-format'
+    apply plugin: 'net.ltgt.errorprone'
 
-apply plugin: 'com.android.library'
+    googleJavaFormat {
+        toolVersion = '1.5'
+        options style: 'AOSP'
+    }
 
-repositories {
-    jcenter()
-    google()
-}
+    apply plugin: 'com.android.library'
 
-dependencies {
-    // NOTE: Updating ErrorProne introduces new checks that may cause the build to fail. Pin to a
-    // specific version to control these updates.
-    errorprone("com.google.errorprone:error_prone_core:2.3.2")
-    // ErrorProne requires a JDK 9 compiler, so pull one in as a dependency since we use Java 8:
-    // https://github.com/tbroyer/gradle-errorprone-plugin#jdk-8-support
-    errorproneJavac("com.google.errorprone:javac:9+181-r4173-1")
-}
+    dependencies {
+        // NOTE: Updating ErrorProne introduces new checks that may cause the build to fail. Pin to a
+        // specific version to control these updates.
+        errorprone("com.google.errorprone:error_prone_core:2.3.2")
+        // ErrorProne requires a JDK 9 compiler, so pull one in as a dependency since we use Java 8:
+        // https://github.com/tbroyer/gradle-errorprone-plugin#jdk-8-support
+        errorproneJavac("com.google.errorprone:javac:9+181-r4173-1")
+    }
+
+    group = 'com.android.volley'
+    version = '1.2.1-SNAPSHOT'
+
+    android {
+        useLibrary 'org.apache.http.legacy'
 
-group = 'com.android.volley'
-version = '1.2.1-SNAPSHOT'
+        compileSdkVersion 28
+        buildToolsVersion = '28.0.3'
 
-android {
-    compileSdkVersion 28
-    buildToolsVersion = '28.0.3'
+        defaultConfig {
+            minSdkVersion 8
+        }
 
-    defaultConfig {
-        minSdkVersion 8
+        compileOptions {
+            sourceCompatibility JavaVersion.VERSION_1_7
+            targetCompatibility JavaVersion.VERSION_1_7
+        }
     }
-}
 
-tasks.withType(JavaCompile) {
-    options.errorprone {
-        check("ParameterComment", CheckSeverity.ERROR)
+    tasks.withType(JavaCompile) {
+        options.errorprone {
+            check("ParameterComment", net.ltgt.gradle.errorprone.CheckSeverity.ERROR)
+        }
+        options.compilerArgs << "-Xlint:unchecked" << "-Werror"
     }
-}
 
-apply from: 'rules.gradle'
-apply from: 'publish.gradle'
+    if (it.name != 'testing') {
+        apply from: '../publish.gradle'
+    }
+}

core/build.gradle

@@ -0,0 +1,28 @@
+android {
+    defaultConfig {
+        consumerProguardFiles 'consumer-proguard-rules.pro'
+    }
+}
+
+dependencies {
+    implementation "androidx.annotation:annotation:1.0.1"
+
+    testImplementation project(":testing")
+    testImplementation "junit:junit:4.12"
+    testImplementation "org.hamcrest:hamcrest-library:1.3"
+    testImplementation "org.mockito:mockito-core:2.19.0"
+    testImplementation "org.robolectric:robolectric:3.4.2"
+}
+
+publishing {
+    publications {
+        library(MavenPublication) {
+            artifactId 'volley'
+            pom {
+                name = 'Volley'
+                description = 'An HTTP library that makes networking for Android apps easier and, most importantly, faster.'
+            }
+            artifact "$buildDir/outputs/aar/core-release.aar"
+        }
+    }
+}

cronet/build.gradle

@@ -0,0 +1,24 @@
+dependencies {
+    implementation project(":core")
+    implementation "androidx.annotation:annotation:1.0.1"
+    compileOnly "org.chromium.net:cronet-embedded:76.3809.111"
+
+    testImplementation project(":testing")
+    testImplementation "org.chromium.net:cronet-embedded:76.3809.111"
+    testImplementation "junit:junit:4.12"
+    testImplementation "org.mockito:mockito-core:2.19.0"
+    testImplementation "org.robolectric:robolectric:3.4.2"
+}
+
+publishing {
+    publications {
+        library(MavenPublication) {
+            artifactId 'volley-cronet'
+            pom {
+                name = 'Volley Cronet'
+                description = 'Cronet support for Volley.'
+            }
+            artifact "$buildDir/outputs/aar/cronet-release.aar"
+        }
+    }
+}

cronet/src/main/AndroidManifest.xml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest package="com.android.volley.cronet" />

publish.gradle

@@ -10,6 +10,12 @@ task javadoc(type: Javadoc) {
     classpath += project.files(android.getBootClasspath().join(File.pathSeparator))
 }
 
+afterEvaluate {
+    javadoc.classpath += files(android.libraryVariants.collect { variant ->
+        variant.getJavaCompile().classpath.files
+    })
+}
+
 task javadocJar(type: Jar, dependsOn: javadoc) {
     classifier = 'javadoc'
     from javadoc.destinationDir
@@ -24,11 +30,9 @@ publishing {
     publications {
         library(MavenPublication) {
             groupId 'com.android.volley'
-            artifactId 'volley'
             version project.version
             pom {
                 name = 'Volley'
-                description = 'An HTTP library that makes networking for Android apps easier and, most importantly, faster.'
                 url = 'https://github.com/google/volley'
                 packaging 'aar'
                 licenses {
@@ -51,7 +55,6 @@ publishing {
             }
 
             // Release AAR, Sources, and JavaDoc
-            artifact "$buildDir/outputs/aar/volley-release.aar"
             artifact sourcesJar
             artifact javadocJar
         }

settings.gradle

@@ -0,0 +1,4 @@
+rootProject.name = 'volley'
+include 'core'
+include 'cronet'
+include 'testing'

testing/build.gradle

@@ -0,0 +1,4 @@
+dependencies {
+    implementation project(":core")
+}
+

testing/src/main/AndroidManifest.xml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest package="com.android.volley.testing" />