Add --incompatible_use_aapt2_by_default incompatible change (IC) flag…

… for enabling aapt2 by default in Bazel.

FR Ref: #4103
IC Ref: #6907

RELNOTES: New incompatible change flag for defaulting to aapt2 in Android builds: `--incompatible_use_aapt2_by_default`. To build with aapt2 today, pass the flag `--incompatible_use_aapt2_by_default=true` or `--android_aapt=aapt2`, or set the `aapt_version`  to `aapt2` on your `android_binary` or `android_local_test` target.
PiperOrigin-RevId: 225593174

src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java

@@ -240,6 +240,23 @@ public static AndroidAaptVersion chooseTargetAaptVersion(RuleContext ruleContext
       return null;
     }
 
+    /**
+     * Select the aapt version for resource processing actions, based on the combination of
+     * --android_aapt flag, aapt_version target attribute, and --incompatible_use_aapt2_by_default
+     * flag.
+     *
+     * <p>Order of precedence:
+     * <li>1. --android_aapt flag
+     * <li>2. 'aapt_version' attribute on target
+     * <li>3. --incompatible_use_aapt2_by_default flag
+     *
+     * @param dataContext the Android data context for detecting aapt2 and fetching Android configs
+     * @param errorConsumer the rule context for reporting errors during version selection
+     * @param attributeString if not null, the aapt version specified by the 'aapt_version' target
+     *     attribute
+     * @return the selected version: aapt or aapt2
+     * @throws RuleErrorException error if aapt2 is requested but it's not available in the SDK
+     */
     @Nullable
     public static AndroidAaptVersion chooseTargetAaptVersion(
         AndroidDataContext dataContext,
@@ -257,8 +274,21 @@ public static AndroidAaptVersion chooseTargetAaptVersion(
         throw errorConsumer.throwWithRuleError(
             "aapt2 processing requested but not available on the android_sdk");
       }
-      // If version is auto, assume aapt.
-      return version == AndroidAaptVersion.AUTO ? AAPT : version;
+
+      if (version != AndroidAaptVersion.AUTO) {
+        return version;
+      }
+
+      // At this point, the version is still auto. If the user passes
+      // --incompatible_use_aapt2_by_default explicitly or implicitly via
+      // --all_incompatible_changes, use aapt2 by default.
+      //
+      // We use the --incompatible_use_aapt2_by_default flag to signal a breaking change in Bazel.
+      // This is required by the Bazel Incompatible Changes policy.
+      //
+      // TODO(jingwen): We can remove the incompatible change flag only when the depot migration is
+      // complete and the default value of --android_aapt is switched from `auto` to `aapt2`.
+      return dataContext.getAndroidConfig().incompatibleChangeUseAapt2ByDefault() ? AAPT2 : AAPT;
     }
   }
 
@@ -867,6 +897,21 @@ public static class Options extends FragmentOptions {
         help = "Tracking flag for when busybox workers are enabled.")
     public boolean persistentBusyboxTools;
 
+    @Option(
+        name = "incompatible_use_aapt2_by_default",
+        documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
+        effectTags = {OptionEffectTag.LOSES_INCREMENTAL_STATE, OptionEffectTag.AFFECTS_OUTPUTS},
+        metadataTags = {
+          OptionMetadataTag.INCOMPATIBLE_CHANGE,
+          OptionMetadataTag.TRIGGERED_BY_ALL_INCOMPATIBLE_CHANGES
+        },
+        defaultValue = "false",
+        help =
+            "Switch the Android rules to use aapt2 by default for resource processing. "
+                + "To resolve issues when migrating your app to build with aapt2, see "
+                + "https://developer.android.com/studio/command-line/aapt2#aapt2_changes")
+    public boolean incompatibleUseAapt2ByDefault;
+
     @Override
     public FragmentOptions getHost() {
       Options host = (Options) super.getHost();
@@ -954,6 +999,9 @@ public ImmutableSet<Class<? extends FragmentOptions>> requiredOptions() {
   private final boolean persistentBusyboxTools;
   private final boolean filterRJarsFromAndroidTest;
 
+  // Incompatible changes
+  private final boolean incompatibleUseAapt2ByDefault;
+
   private AndroidConfiguration(Options options) throws InvalidConfigurationException {
     this.sdk = options.sdk;
     this.useIncrementalNativeLibs = options.incrementalNativeLibs;
@@ -997,6 +1045,7 @@ private AndroidConfiguration(Options options) throws InvalidConfigurationExcepti
     this.dataBindingV2 = options.dataBindingV2;
     this.persistentBusyboxTools = options.persistentBusyboxTools;
     this.filterRJarsFromAndroidTest = options.filterRJarsFromAndroidTest;
+    this.incompatibleUseAapt2ByDefault = options.incompatibleUseAapt2ByDefault;
 
     if (incrementalDexingShardsAfterProguard < 0) {
       throw new InvalidConfigurationException(
@@ -1208,6 +1257,10 @@ public boolean persistentBusyboxTools() {
     return persistentBusyboxTools;
   }
 
+  public boolean incompatibleChangeUseAapt2ByDefault() {
+    return incompatibleUseAapt2ByDefault;
+  }
+
   @Override
   public String getOutputDirectoryName() {
     return configurationDistinguisher.suffix;

src/test/java/com/google/devtools/build/lib/rules/android/AndroidResourcesTest.java

@@ -511,6 +511,28 @@ public void testProcessBinaryDataGeneratesProguardOutput() throws Exception {
     assertThat(resourceApk.getMainDexProguardConfig()).isNotNull();
   }
 
+  @Test
+  public void test_incompatibleUseAapt2ByDefaultEnabled_targetsAapt2() throws Exception {
+    mockAndroidSdkWithAapt2();
+    useConfiguration("--android_sdk=//sdk:sdk", "--incompatible_use_aapt2_by_default");
+    RuleContext ruleContext =
+        getRuleContext(
+            "android_binary", "aapt_version = 'auto',", "manifest = 'AndroidManifest.xml',");
+    assertThat(AndroidAaptVersion.chooseTargetAaptVersion(ruleContext))
+        .isEqualTo(AndroidAaptVersion.AAPT2);
+  }
+
+  @Test
+  public void test_incompatibleUseAapt2ByDefaultDisabled_targetsAapt() throws Exception {
+    mockAndroidSdkWithAapt2();
+    useConfiguration("--android_sdk=//sdk:sdk", "--noincompatible_use_aapt2_by_default");
+    RuleContext ruleContext =
+        getRuleContext(
+            "android_binary", "aapt_version = 'auto',", "manifest = 'AndroidManifest.xml',");
+    assertThat(AndroidAaptVersion.chooseTargetAaptVersion(ruleContext))
+        .isEqualTo(AndroidAaptVersion.AAPT);
+  }
+
   /**
    * Validates that a parse action was invoked correctly. Returns the {@link ParsedAndroidResources}
    * for further validation.