OSS Android: architecture.gradle base setup

Summary:
Introduced `architecture.gradle` that sets up pluggable build-time codegen steps for Gradle so that:
* Libraries, including core ReactAndroid, can produce the new architecture codegen (NativeModule **Java** specs in this diff) during build time
* Hosting app (e.g. RNTester) can produce its own set of codegen specs separately

**Please note that this is still work in progress, hence app templates have not been updated to use it yet.**

In order to activate this setup, the env variable `USE_CODEGEN=1` must be set. Eventually, this var will be removed from the logic.

With this change, RNTester:
* Will see all the generated specs populated in the Gradle build dir, which should be equivalent to the currently [**checked in version**](https://github.com/facebook/react-native/tree/master/ReactAndroid/src/main/java/com/facebook/fbreact/specs).
* The specs will compile, but **have not been validated** vs the existing NativeModule .java classes through out the core -- that will be the next step
* The specs are under `com.facebook.fbreact.specs.beta` namespace, which will be configurable in the future. `.beta` is added to avoid conflict with the existing files in the repo.

### Is this all we need to enable TurboModule in Android?
No. There are a few more pieces needed:
* C++ codegen output for JNI layer for each NativeModule spec
* The C++ module lookup for TurboModule Manager
* The JNI build setup in Gradle for these C++ output
* Toggle to enable TurboModule system in the entire app

Changelog: [Internal]

Reviewed By: JoshuaGross

Differential Revision: D22838581

fbshipit-source-id: d972e2fbb37bdbd3354e72b014fc8bb27a33b9ac

RNTester/android/app/build.gradle

@@ -60,7 +60,17 @@ plugins {
  *   // date; if you have any other folders that you want to ignore for performance reasons (gradle
  *   // indexes the entire tree), add them here. Alternatively, if you have JS files in android/
  *   // for example, you might want to remove it from here.
- *   inputExcludes: ["android/**", "ios/**"]
+ *   inputExcludes: ["android/**", "ios/**"],
+ *
+ *   // Root dir for all JS files for the app. Defaults to `root` above.
+ *   jsRootDir: "../..",
+ *
+ *   // Enable react-native-codegen during build time.
+ *   enableCodegen: true,
+ *
+ *   // Java package name to use for any codegen artifacts produced during build time.
+ *   // Defaults to "com.facebook.fbreact.specs".
+ *   codegenJavaPackageName: "com.facebook.fbreact.specs",
  * ]
  */
 
@@ -72,7 +82,9 @@ project.ext.react = [
     inputExcludes: ["android/**", "./**", ".gradle/**"],
     composeSourceMapsPath: "$rootDir/scripts/compose-source-maps.js",
     hermesCommand: "../../../node_modules/hermes-engine/%OS-BIN%/hermesc",
-    enableHermesForVariant: { def v -> v.name.contains("hermes") }
+    enableHermesForVariant: { def v -> v.name.contains("hermes") },
+    jsRootDir: "$rootDir/RNTester",
+    enableCodegen: System.getenv('USE_CODEGEN'),
 ]
 
 apply from: "../../../react.gradle"

ReactAndroid/build.gradle

@@ -468,3 +468,8 @@ dependencies {
 }
 
 apply(from: "release.gradle")
+apply(from: "../architecture.gradle");
+generateNativeArtifactsFromJavaScript([
+    enableCodegen: System.getenv("USE_CODEGEN"),
+    jsRootDir: "${file('../Libraries')}",
+])

architecture.gradle

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+
+def codegenDir = "$rootDir/packages/react-native-codegen";
+def codegenGenerateSchemaCli = "$codegenDir/lib/cli/combine/combine-js-to-schema-cli.js";
+def codegenGenerateNativeModuleSpecsCli = "$rootDir/scripts/generate-native-modules-specs-cli.js";
+def schemaFile = "schema.json";
+
+// TODO: Consider building Gradle plugin instead.
+
+/**
+ * The config is derived from app-level `project.react`.
+ */
+ext.generateNativeArtifactsFromJavaScript = { Map config ->
+  def nodeExecutableAndArgs = config.nodeExecutableAndArgs ?: ["node"];
+  def jsRootDir = config.jsRootDir ?: config.root;
+
+  if (!config.enableCodegen) {
+    return;
+  }
+
+  // 1. Create build dir
+  def generatedSrcDir = file("$buildDir/generated/source/codegen");
+
+  // 2. Produce schema from JS files.
+  task generateCodegenSchemaFromJavaScript(type: Exec) {
+    doFirst {
+      generatedSrcDir.deleteDir()
+      generatedSrcDir.mkdirs()
+    }
+
+    def schemaOutputFile = file("$generatedSrcDir/$schemaFile");
+
+    inputs.files fileTree(dir: codegenDir)
+    inputs.files fileTree(dir: jsRootDir)
+    outputs.file(schemaOutputFile)
+
+    def execCommands = ["yarn"] + nodeExecutableAndArgs + [
+      codegenGenerateSchemaCli,
+      "$schemaOutputFile",
+      jsRootDir,
+    ];
+    commandLine execCommands
+
+    ext.schema = {
+      schemaOutputFile
+    }
+  }
+
+  // 3. Generate Java code from schema
+  task generateCodegenArtifactsFromSchema(dependsOn: 'generateCodegenSchemaFromJavaScript', type: Exec) {
+
+    def generatedSchema = tasks.generateCodegenSchemaFromJavaScript.schema();
+    def javaPackageName = config.codegenJavaPackageName ?: "com.facebook.fbreact.specs.beta";
+    def javaPackageDir = javaPackageName.replace(".", "/");
+    def outputDir = file("$generatedSrcDir/java/$javaPackageDir");
+
+    inputs.files fileTree(dir: codegenDir)
+    inputs.files generatedSchema
+    outputs.dir(outputDir)
+
+    def execCommands = ["yarn"] + nodeExecutableAndArgs + [
+      codegenGenerateNativeModuleSpecsCli,
+      "android",
+      "$generatedSchema",
+      "$outputDir",
+    ];
+    commandLine execCommands
+  }
+
+  // 4. add deps + srcs
+  preBuild.dependsOn generateCodegenArtifactsFromSchema
+
+  android {
+    sourceSets {
+      main {
+        java {
+          srcDirs += "$generatedSrcDir/java"
+        }
+      }
+    }
+  }
+}

react.gradle

@@ -349,3 +349,6 @@ afterEvaluate {
         }
     }
 }
+
+apply(from: "$rootDir/architecture.gradle");
+generateNativeArtifactsFromJavaScript(project.react);