[Uber] Add fat_aar rule for bundling Android libraries into a distrib…

README.md

@@ -108,3 +108,21 @@ android_library(
    ...
 )
 ```
+
+## Available Rules
+
+- **`android_binary`** - Builds an Android APK
+- **`android_library`** - Builds an Android library
+- **`android_application`** - Builds an Android application bundle (AAB)
+- **`fat_aar`** - Bundles multiple Android libraries into a single AAR file (see [rules/fat_aar](rules/fat_aar/))
+- **`fat_aar_pom`** - Generates a Maven POM from a fat_aar's excluded dependencies
+
+For a complete list of rules, see the [rules.bzl](rules/rules.bzl) file.
+
+## Examples
+
+See the [examples](examples/) directory for sample projects:
+
+- **[basicapp](examples/basicapp/)** - Basic Android application
+- **[bundle](examples/bundle/)** - Android application bundle (AAB)
+- **[fat_aar](examples/fat_aar/)** - Fat AAR with resources, assets, and native libraries

examples/fat_aar/AndroidManifest.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.example.fat_aar">
+</manifest>

examples/fat_aar/BUILD

@@ -0,0 +1,44 @@
+load("//rules/android_library:rule.bzl", "android_library")
+load("//rules/fat_aar:rule.bzl", "fat_aar")
+
+# Library with resources and assets
+android_library(
+    name = "lib1",
+    srcs = ["Lib1.java"],
+    manifest = "AndroidManifest.xml",
+    resource_files = glob(["res/**"]),
+    assets = glob(["assets/**"]),
+    assets_dir = "assets",
+)
+
+# Library depending on lib1 (transitive dependency test)
+android_library(
+    name = "lib2",
+    srcs = ["Lib2.java"],
+    manifest = "AndroidManifest.xml",
+    deps = [":lib1"],
+)
+
+# Native library
+cc_library(
+    name = "native_lib",
+    srcs = ["jni/arm64-v8a/libnative.so"],
+)
+
+# Fat AAR bundling all transitive dependencies
+fat_aar(
+    name = "bundled",
+    min_sdk_version = "21",
+    deps = [
+        ":lib2",
+        ":native_lib",
+    ],
+)
+
+# Fat AAR with exclusions (e.g., exclude external dependencies)
+fat_aar(
+    name = "bundled_filtered",
+    min_sdk_version = "21",
+    exclude = ["@maven//"],
+    deps = [":lib2"],
+)

examples/fat_aar/Lib1.java

@@ -0,0 +1,7 @@
+package com.example.fat_aar;
+
+public class Lib1 {
+    public String getMessage() {
+        return "Hello from Lib1";
+    }
+}

examples/fat_aar/Lib2.java

@@ -0,0 +1,9 @@
+package com.example.fat_aar;
+
+public class Lib2 {
+    private Lib1 lib1 = new Lib1();
+
+    public String getCombinedMessage() {
+        return "Lib2 says: " + lib1.getMessage();
+    }
+}

examples/fat_aar/README.md

@@ -0,0 +1,60 @@
+# Fat AAR Example
+
+This example demonstrates how to use the `fat_aar` rule to bundle multiple Android libraries and their transitive dependencies into a single AAR file.
+
+## Structure
+
+- **lib1**: Android library with resources, layouts, and assets
+- **lib2**: Android library that depends on lib1 (demonstrates transitive bundling)
+- **native_lib**: Native library (demonstrates native library bundling)
+
+## Targets
+
+### `bundled`
+A fat AAR that bundles all transitive dependencies including:
+- Java/Kotlin classes from lib1 and lib2
+- Resources from all libraries
+- Assets from all libraries
+- Native libraries
+- Merged AndroidManifest.xml
+
+```bash
+bazel build //examples/fat_aar:bundled
+```
+
+### `bundled_filtered`
+A fat AAR with exclusions - demonstrates filtering out external dependencies:
+```bash
+bazel build //examples/fat_aar:bundled_filtered
+```
+
+## What Gets Bundled
+
+The `fat_aar` rule automatically collects and bundles:
+
+1. **Classes (classes.jar)**: All Java/Kotlin bytecode from transitive dependencies
+2. **Resources (res/)**: All resources from transitive android_library targets
+3. **Assets (assets/)**: All assets from transitive dependencies
+4. **Native Libraries (jni/)**: Native .so files for all architectures
+5. **AndroidManifest.xml**: Merged manifest from all libraries
+6. **R.txt**: Combined R.txt for resource IDs
+7. **proguard.txt**: Merged ProGuard rules
+
+## Excluding Dependencies
+
+Use the `exclude` attribute to filter out dependencies (e.g., external Maven dependencies):
+
+```python
+fat_aar(
+    name = "my_aar",
+    exclude = ["@maven//"],  # Exclude all Maven dependencies
+    deps = [":my_lib"],
+)
+```
+
+## Output
+
+The fat AAR is a standard Android AAR file that can be:
+- Published to Maven/Artifactory
+- Consumed by other Android projects (Gradle or Bazel)
+- Distributed as a reusable component

examples/fat_aar/assets/sample_asset.txt

@@ -0,0 +1 @@
+This is a sample asset file to test asset bundling in fat_aar.

examples/fat_aar/jni/arm64-v8a/libnative.so

@@ -0,0 +1 @@
+FAKE_NATIVE_LIB_FOR_TESTING

examples/fat_aar/res/layout/lib_layout.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:orientation="vertical">
+
+    <TextView
+        android:id="@+id/text_view"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="@string/hello" />
+</LinearLayout>

examples/fat_aar/res/values/strings.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">Fat AAR Example</string>
+    <string name="hello">Hello from resources</string>
+</resources>

rules/BUILD

@@ -109,6 +109,7 @@ bzl_library(
     ],
     visibility = [
         "//mobile_install:__pkg__",
+        "//rules/fat_aar:__pkg__",
         "//stardoc:__pkg__",
         "//test/rules/android_binary/r8_integration:__pkg__",
         "//test/rules/android_sdk_repository:__pkg__",

rules/fat_aar/BUILD

@@ -0,0 +1,18 @@
+load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+
+package(default_visibility = ["//visibility:public"])
+
+exports_files([
+    "add_native_libs.sh",
+    "rule.bzl",
+    "aspect.bzl",
+])
+
+bzl_library(
+    name = "bzl",
+    srcs = glob(["*.bzl"]),
+    visibility = ["//visibility:public"],
+    deps = [
+        "//rules:bzl",
+    ],
+)