Fix R8 --desugar_java8_libs support

.bazelrc

@@ -28,3 +28,4 @@ build:windows --define=protobuf_allow_msvc=true
 
 common --enable_platform_specific_config
 
+common --desugar_java8_libs

rules/android_binary/r8.bzl

@@ -80,6 +80,7 @@ def process_r8(ctx, validation_ctx, jvm_ctx, packaged_resources_ctx, build_info_
 
     android_jar = get_android_sdk(ctx).android_jar
     proguard_specs = proguard.get_proguard_specs(ctx, packaged_resources_ctx.resource_proguard_config)
+    desugared_lib_config = ctx.file._desugared_lib_config
 
     # Get min SDK version from attribute, manifest_values, or depot floor
     effective_min_sdk = min_sdk_version.DEPOT_FLOOR
@@ -107,12 +108,17 @@ def process_r8(ctx, validation_ctx, jvm_ctx, packaged_resources_ctx, build_info_
     args.add(deploy_jar)  # jar to optimize + desugar + dex
     args.add("--pg-map-output", proguard_mappings_output_file)
 
+    r8_inputs = [android_jar, deploy_jar] + proguard_specs
+    if ctx.fragments.android.desugar_java8_libs and desugared_lib_config:
+        args.add("--desugared-lib", desugared_lib_config)
+        r8_inputs.append(desugared_lib_config)
+
     java.run(
         ctx = ctx,
         host_javabase = common.get_host_javabase(ctx),
         executable = get_android_toolchain(ctx).r8.files_to_run,
         arguments = [args],
-        inputs = depset([android_jar, deploy_jar] + proguard_specs, transitive = [neverlink_jars]),
+        inputs = depset(r8_inputs, transitive = [neverlink_jars]),
         outputs = [dexes_zip, proguard_mappings_output_file],
         mnemonic = "AndroidR8",
         jvm_flags = ["-Xmx8G"],

test/rules/android_binary/r8_integration/BUILD

@@ -24,3 +24,13 @@ build_test(
     name = "android_binary_with_neverlink_deps_build_test",
     targets = ["//test/rules/android_binary/r8_integration/java/com/neverlink:android_binary_with_neverlink_deps"],
 )
+
+py_test(
+    name = "r8_desugaring_test",
+    srcs = ["r8_desugaring_test.py"],
+    args = ["$(location @androidsdk//:dexdump)"],
+    data = [
+        "//test/rules/android_binary/r8_integration/java/com/desugaring:desugaring_app_r8",
+        "@androidsdk//:dexdump",
+    ],
+)

test/rules/android_binary/r8_integration/java/com/desugaring/AndroidManifest.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.desugaring" >
+
+    <uses-sdk
+        android:minSdkVersion="28"
+        android:targetSdkVersion="34" />
+
+    <application>
+        <activity
+            android:name="com.desugaring.DesugaringActivity"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

test/rules/android_binary/r8_integration/java/com/desugaring/BUILD

@@ -0,0 +1,16 @@
+load("//rules:rules.bzl", "android_binary", "android_library")
+
+android_library(
+    name = "duration_lib",
+    srcs = ["DurationUser.java"],
+)
+
+android_binary(
+    name = "desugaring_app_r8",
+    srcs = ["DesugaringActivity.java"],
+    manifest = "AndroidManifest.xml",
+    proguard_specs = ["proguard.cfg"],
+    resource_files = glob(["res/**"]),
+    visibility = ["//test/rules/android_binary/r8_integration:__pkg__"],
+    deps = [":duration_lib"],
+)

test/rules/android_binary/r8_integration/java/com/desugaring/DesugaringActivity.java

@@ -0,0 +1,17 @@
+package com.desugaring;
+
+import android.app.Activity;
+import android.os.Bundle;
+import java.time.Duration;
+
+/** Activity that exercises Duration.toSeconds() to test core library desugaring. */
+public class DesugaringActivity extends Activity {
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        // Force the compiler to retain the call to DurationUser.getSeconds
+        long seconds = DurationUser.getSeconds(Duration.ofMinutes(5));
+        setTitle("Seconds: " + seconds);
+    }
+}

test/rules/android_binary/r8_integration/java/com/desugaring/DurationUser.java

@@ -0,0 +1,18 @@
+package com.desugaring;
+
+import java.time.Duration;
+
+/**
+ * A class that uses Duration.toSeconds(), which was added in API 31.
+ * This simulates a third-party library (like Google Nav SDK) that calls
+ * methods not available on all supported API levels.
+ *
+ * Without core library desugaring, this causes NoSuchMethodError on
+ * API 26-30 devices.
+ */
+public class DurationUser {
+    public static long getSeconds(Duration duration) {
+        // Duration.toSeconds() requires API 31+
+        return duration.toSeconds();
+    }
+}

test/rules/android_binary/r8_integration/java/com/desugaring/proguard.cfg

@@ -0,0 +1,2 @@
+-dontobfuscate
+-keep class com.desugaring.DurationUser { *; }

test/rules/android_binary/r8_integration/java/com/desugaring/res/layout/activity_main.xml

@@ -0,0 +1,5 @@
+<?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">
+</LinearLayout>

test/rules/android_binary/r8_integration/java/com/desugaring/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">Desugaring Test</string>
+</resources>

test/rules/android_binary/r8_integration/r8_desugaring_test.py

@@ -0,0 +1,65 @@
+# Copyright 2024 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import subprocess
+import sys
+import unittest
+import zipfile
+
+
+class R8DesugaringTest(unittest.TestCase):
+  """Tests R8 core library desugaring integration."""
+
+  def _get_dexdump_output(self, apk_name):
+    tmp = os.environ["TEST_TMPDIR"]
+    apk_directory = "test/rules/android_binary/r8_integration/java/com/desugaring"
+    apk_path = os.path.join(apk_directory, apk_name)
+    apk_tmp = os.path.join(tmp, apk_name)
+
+    with zipfile.ZipFile(apk_path) as zf:
+      zf.extract("classes.dex", apk_tmp)
+
+    dexdump_proc = subprocess.run(
+        [dexdump, "-d", os.path.join(apk_tmp, "classes.dex")],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        check=True,
+    )
+    return dexdump_proc.stdout.decode()
+
+  def test_duration_to_seconds_is_desugared(self):
+    output = self._get_dexdump_output("desugaring_app_r8.apk")
+
+    # Duration.toSeconds() (API 31) must not appear as a raw call in the DEX.
+    # If present, R8 was not passed --desugared-lib and the call will cause
+    # NoSuchMethodError on API 28-30 devices.
+    self.assertNotIn(
+        "Ljava/time/Duration;.toSeconds:()J",
+        output,
+    )
+
+  def test_desugared_duration_class_present(self):
+    output = self._get_dexdump_output("desugaring_app_r8.apk")
+
+    # The DurationUser class should still be in the DEX (kept by proguard rules)
+    self.assertIn(
+        "Class descriptor  : 'Lcom/desugaring/DurationUser;'",
+        output,
+    )
+
+
+if __name__ == "__main__":
+  dexdump = sys.argv.pop()
+  unittest.main(argv=None)