[deferred components] Handle base module loading units

shell/platform/android/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java

@@ -248,12 +248,14 @@ private ApplicationInfo getApplicationInfo() {
 
   // Obtain and parses the metadata string. An example encoded string is:
   //
-  //    "2:component2,3:component3,4:component1:libcomponent4.so"
+  //    "2:component2,3:component3,4:component1:libcomponent4.so,5:"
   //
   // Where loading unit 2 is included in component2, loading unit 3 is
   // included in component3, and loading unit 4 is included in component1.
   // An optional third parameter can be added to indicate the name of
-  // the shared library of the loading unit.
+  // the shared library of the loading unit. Loading unit 5 maps to an empty
+  // string, indicating it is included in the base module and no dynamic
+  // feature modules need to be downloaded.
   private void initLoadingUnitMappingToComponentNames() {
     String mappingKey = DeferredComponentManager.class.getName() + ".loadingUnitMapping";
     ApplicationInfo applicationInfo = getApplicationInfo();
@@ -269,7 +271,8 @@ private void initLoadingUnitMappingToComponentNames() {
                   + "' is defined in the base module's AndroidManifest.");
         } else {
           for (String entry : rawMappingString.split(",")) {
-            String[] splitEntry = entry.split(":");
+            // Split with -1 param to include empty string following trailing ":"
+            String[] splitEntry = entry.split(":", -1);
             int loadingUnitId = Integer.parseInt(splitEntry[0]);
             loadingUnitIdToComponentNames.put(loadingUnitId, splitEntry[1]);
             if (splitEntry.length > 2) {
@@ -290,6 +293,13 @@ public void installDeferredComponent(int loadingUnitId, String componentName) {
       return;
     }
 
+    // Handle a loading unit that is included in the base module that does not need download.
+    if (resolvedComponentName.equals("") && loadingUnitId > 0) {
+      // No need to load assets as base assets are already loaded.
+      loadDartLibrary(loadingUnitId, resolvedComponentName);
+      return;
+    }
+
     SplitInstallRequest request =
         SplitInstallRequest.newBuilder().addModule(resolvedComponentName).build();
 

shell/platform/android/test/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManagerTest.java

@@ -184,6 +184,37 @@ public void downloadCallsJNIFunctionsWithSharedLibraryNameFromManifest()
     assertEquals(jni.assetBundlePath, "custom_assets");
   }
 
+  @Test
+  public void manifestMappingHandlesBaseModuleEmptyString() throws NameNotFoundException {
+    TestFlutterJNI jni = new TestFlutterJNI();
+
+    Bundle bundle = new Bundle();
+    bundle.putString(
+        PlayStoreDeferredComponentManager.MAPPING_KEY, "123:module:custom_name.so,3:,4:");
+    bundle.putString(ApplicationInfoLoader.PUBLIC_FLUTTER_ASSETS_DIR_KEY, "custom_assets");
+
+    Context spyContext = createSpyContext(bundle);
+    doReturn(null).when(spyContext).getAssets();
+
+    String soTestFilename = "libapp.so-3.part.so";
+    String soTestPath = "test/path/" + soTestFilename;
+    doReturn(new File(soTestPath)).when(spyContext).getFilesDir();
+    PlayStoreDeferredComponentManager playStoreManager =
+        new PlayStoreDeferredComponentManager(spyContext, jni);
+    jni.setDeferredComponentManager(playStoreManager);
+    assertEquals(jni.loadingUnitId, 0);
+
+    playStoreManager.installDeferredComponent(3, null);
+    assertEquals(jni.loadDartDeferredLibraryCalled, 1);
+    assertEquals(jni.updateAssetManagerCalled, 0); // no assets to load for base
+    assertEquals(jni.deferredComponentInstallFailureCalled, 0);
+
+    assertEquals(jni.searchPaths[0], soTestFilename);
+    assertTrue(jni.searchPaths[1].endsWith(soTestPath));
+    assertEquals(jni.searchPaths.length, 2);
+    assertEquals(jni.loadingUnitId, 3);
+  }
+
   @Test
   public void searchPathsAddsApks() throws NameNotFoundException {
     TestFlutterJNI jni = new TestFlutterJNI();