Add an is_android option to facilitate exec toolchain selection

RELNOTES:None.
PiperOrigin-RevId: 562925627
Change-Id: I30a83d83d8d97947b446cb53ed6555c87b367b60

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

@@ -1107,6 +1107,19 @@ public static class Options extends FragmentOptions {
                 + " transition` with changed options to avoid potential action conflicts.")
     public boolean androidPlatformsTransitionsUpdateAffected;
 
+    @Option(
+        name = "is_android",
+        defaultValue = "false",
+        documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+        effectTags = OptionEffectTag.BAZEL_INTERNAL_CONFIGURATION,
+        help =
+            "This option exists for the purposes of enabling the toolchain resolution mechanism"
+                + " to select a different `exec` toolchain when targeting Android. An example use"
+                + " case is Rust: The Rust toolchain has a requirement that certain types of"
+                + " libraries (proc-macro) that are built in `exec` mode *have* to be compiled with"
+                + " the same toolchain as the libraries built in `target` mode.")
+    public boolean isAndroid;
+
     @Override
     public FragmentOptions getExec() {
       Options exec = (Options) super.getExec();
@@ -1137,6 +1150,7 @@ public FragmentOptions getExec() {
       exec.persistentBusyboxTools = persistentBusyboxTools;
       exec.persistentMultiplexBusyboxTools = persistentMultiplexBusyboxTools;
       exec.disableNativeAndroidRules = disableNativeAndroidRules;
+      exec.isAndroid = isAndroid;
 
       // Unless the build was started from an Android device, exec means MAIN.
       exec.configurationDistinguisher = ConfigurationDistinguisher.MAIN;
@@ -1193,6 +1207,7 @@ public FragmentOptions getExec() {
   private final boolean hwasan;
   private final boolean getJavaResourcesFromOptimizedJar;
   private final boolean includeProguardLocationReferences;
+  private final boolean isAndroid;
 
   public AndroidConfiguration(BuildOptions buildOptions) throws InvalidConfigurationException {
     Options options = buildOptions.get(Options.class);
@@ -1254,6 +1269,7 @@ public AndroidConfiguration(BuildOptions buildOptions) throws InvalidConfigurati
     this.hwasan = options.hwasan;
     this.getJavaResourcesFromOptimizedJar = options.getJavaResourcesFromOptimizedJar;
     this.includeProguardLocationReferences = options.includeProguardLocationReferences;
+    this.isAndroid = options.isAndroid;
 
     if (incrementalDexingShardsAfterProguard < 0) {
       throw new InvalidConfigurationException(
@@ -1534,6 +1550,10 @@ boolean outputLibraryMergedAssets() {
     return outputLibraryMergedAssets;
   }
 
+  boolean isAndroid() {
+    return isAndroid;
+  }
+
   /** Returns the label provided with --legacy_main_dex_list_generator, if any. */
   // TODO(b/147692286): Move R8's main dex list tool into tool repository.
   @StarlarkConfigurationField(

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

@@ -74,7 +74,7 @@ public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler) {
     // 2. Otherwise, leave --platforms alone (this will probably lead to build errors).
     if (!androidOptions.androidPlatforms.isEmpty()) {
       // If the current value of --platforms is not one of the values of --android_platforms, change
-      // it to be the first one. If the curent --platforms is part of --android_platforms, leave it
+      // it to be the first one. If the current --platforms is part of --android_platforms, leave it
       // as-is.
       // NOTE: This does not handle aliases at all, so if someone is using aliases with platform
       // definitions this check will break.
@@ -90,6 +90,8 @@ public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler) {
       newOptions.get(CppOptions.class).enableCcToolchainResolution = true;
     }
 
+    newOptions.get(AndroidConfiguration.Options.class).isAndroid = true;
+
     if (androidOptions.androidPlatformsTransitionsUpdateAffected) {
       ImmutableSet.Builder<String> affected = ImmutableSet.builder();
       if (!options
@@ -102,6 +104,10 @@ public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler) {
           != newOptions.get(CppOptions.class).enableCcToolchainResolution) {
         affected.add("//command_line_option:incompatible_enable_cc_toolchain_resolution");
       }
+      if (options.get(AndroidConfiguration.Options.class).isAndroid
+          != newOptions.get(AndroidConfiguration.Options.class).isAndroid) {
+        affected.add("//command_line_option:is_android");
+      }
       FunctionTransitionUtil.updateAffectedByStarlarkTransition(
           newOptions.get(CoreOptions.class), affected.build());
     }

src/test/java/com/google/devtools/build/lib/rules/android/AndroidDataBindingV2Test.java

@@ -339,7 +339,7 @@ public void dataBindingAnnotationProcessorFlags_v3_4() throws Exception {
         (JavaCompileAction)
             getGeneratingAction(getFirstArtifactEndingWith(allArtifacts, "app.jar"));
     String dataBindingFilesDir =
-        targetConfig
+        getConfiguration(ctapp)
             .getBinDirectory(RepositoryName.MAIN)
             .getExecPath()
             .getRelative("java/android/binary/databinding/app")
@@ -1214,7 +1214,7 @@ public void dataBinding_androidLocalTest_dataBindingEnabled_usesDataBindingFlags
             getGeneratingAction(
                 getFirstArtifactEndingWith(allArtifacts, "databinding_enabled_test-class.jar"));
     String dataBindingFilesDir =
-        targetConfig
+        getConfiguration(testTarget)
             .getBinDirectory(RepositoryName.MAIN)
             .getExecPath()
             .getRelative("javatests/android/test/databinding/databinding_enabled_test")

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

@@ -190,7 +190,10 @@ public void testTestExecutableRunfiles() throws Exception {
                 .toList());
     assertThat(runfiles.stream().map(Artifact::toString).collect(toImmutableList()))
         .containsAtLeast(
-            getDeviceFixtureScript(getConfiguredTarget("//javatests/com/app:device_fixture"))
+            getDeviceFixtureScript(
+                    getDirectPrerequisite(
+                        androidInstrumentationTest.getConfiguredTarget(),
+                        "//javatests/com/app:device_fixture"))
                 .toString(),
             getInstrumentationApk(getConfiguredTarget("//javatests/com/app:instrumentation_app"))
                 .toString(),