Remove KitKat support.

This commit does a bunch of CI and build clean-up, but its primary set
of changes is to remove references and code corresponding to KitKat.

.github/CODEOWNERS

@@ -259,9 +259,6 @@ WORKSPACE @oppia/android-app-infrastructure-reviewers
 # Proguard configurations for Bazel builds.
 /config/proguard/ @oppia/android-dev-workflow-reviewers
 
-# Configuration for KitKat-specific curated builds.
-/config/kitkat_main_dex_class_list.txt @oppia/android-dev-workflow-reviewers
-
 # Specific manifest files specifically required for Bazel builds.
 /app/src/main/AppAndroidManifest.xml @oppia/android-dev-workflow-reviewers
 /app/src/main/DatabindingAdaptersManifest.xml @oppia/android-dev-workflow-reviewers

.github/workflows/unit_tests.yml

@@ -106,7 +106,6 @@ jobs:
       max-parallel: 10
       matrix: ${{ fromJson(needs.bazel_compute_affected_targets.outputs.matrix) }}
     env:
-      ENABLE_CACHING: false
       CACHE_DIRECTORY: ~/.bazel_cache
     steps:
       - uses: actions/checkout@v2
@@ -206,57 +205,7 @@ jobs:
           echo "build --disk_cache=$EXPANDED_BAZEL_CACHE_PATH" >> $HOME/.bazelrc
         shell: bash
 
-      # See explanation in bazel_build_app for how this is installed.
-      - name: Install git-secret (non-fork only)
-        if: ${{ env.ENABLE_CACHING == 'true' && ((github.ref == 'refs/heads/develop' && github.event_name == 'push') || (github.event.pull_request.head.repo.full_name == 'oppia/oppia-android')) }}
-        shell: bash
-        run: |
-          cd $HOME
-          mkdir -p $HOME/gitsecret
-          git clone https://github.com/sobolevn/git-secret.git git-secret
-          cd git-secret && make build
-          PREFIX="$HOME/gitsecret" make install
-          echo "$HOME/gitsecret" >> $GITHUB_PATH
-          echo "$HOME/gitsecret/bin" >> $GITHUB_PATH
-
-      - name: Decrypt secrets (non-fork only)
-        if: ${{ env.ENABLE_CACHING == 'true' && ((github.ref == 'refs/heads/develop' && github.event_name == 'push') || (github.event.pull_request.head.repo.full_name == 'oppia/oppia-android')) }}
-        env:
-          GIT_SECRET_GPG_PRIVATE_KEY: ${{ secrets.GIT_SECRET_GPG_PRIVATE_KEY }}
-        run: |
-          cd $HOME
-          # NOTE TO DEVELOPERS: Make sure to never print this key directly to stdout!
-          echo $GIT_SECRET_GPG_PRIVATE_KEY | base64 --decode > ./git_secret_private_key.gpg
-          gpg --import ./git_secret_private_key.gpg
-          cd $GITHUB_WORKSPACE
-          git secret reveal
-
-      # See https://www.cyberciti.biz/faq/unix-for-loop-1-to-10/ for for-loop reference.
-      - name: Build Oppia Tests (with caching, non-fork only)
-        if: ${{ env.ENABLE_CACHING == 'true' && ((github.ref == 'refs/heads/develop' && github.event_name == 'push') || (github.event.pull_request.head.repo.full_name == 'oppia/oppia-android')) }}
-        env:
-          BAZEL_REMOTE_CACHE_URL: ${{ secrets.BAZEL_REMOTE_CACHE_URL }}
-          BAZEL_TEST_TARGETS: ${{ env.BAZEL_TEST_TARGETS }}
-        run: |
-          # Attempt to build 5 times in case there are flaky builds.
-          # TODO(#3759): Remove this once there are no longer app test build failures.
-          i=0
-          # Disable exit-on-first-failure.
-          set +e
-          while [ $i -ne 5 ]; do
-            i=$(( $i+1 ))
-            echo "Attempt $i/5 to build test targets"
-            bazel build --keep_going --remote_http_cache=$BAZEL_REMOTE_CACHE_URL --google_credentials=./config/oppia-dev-workflow-remote-cache-credentials.json -- $BAZEL_TEST_TARGETS
-          done
-          # Capture the error code of the final command run (which should be a success if there isn't a real build failure).
-          last_error_code=$?
-          # Reenable exit-on-first-failure.
-          set -e
-          # Exit only if the most recent exit was a failure (by using a subshell).
-          (exit $last_error_code)
-
-      - name: Build Oppia Tests (without caching, or on a fork)
-        if: ${{ env.ENABLE_CACHING == 'false' || ((github.ref != 'refs/heads/develop' || github.event_name != 'push') && (github.event.pull_request.head.repo.full_name != 'oppia/oppia-android')) }}
+      - name: Build Oppia Tests
         env:
           BAZEL_TEST_TARGETS: ${{ env.BAZEL_TEST_TARGETS }}
         run: |
@@ -276,30 +225,8 @@ jobs:
           set -e
           # Exit only if the most recent exit was a failure (by using a subshell).
           (exit $last_error_code)
-      - name: Run Oppia Tests (with caching, non-fork only)
-        if: ${{ env.ENABLE_CACHING == 'true' && ((github.ref == 'refs/heads/develop' && github.event_name == 'push') || (github.event.pull_request.head.repo.full_name == 'oppia/oppia-android')) }}
-        env:
-          BAZEL_REMOTE_CACHE_URL: ${{ secrets.BAZEL_REMOTE_CACHE_URL }}
-          BAZEL_TEST_TARGETS: ${{ env.BAZEL_TEST_TARGETS }}
-        run: |
-          # Attempt to build 5 times in case there are flaky builds.
-          # TODO(#3970): Remove this once there are no longer app test build failures.
-          i=0
-          # Disable exit-on-first-failure.
-          set +e
-          while [ $i -ne 5 ]; do
-            i=$(( $i+1 ))
-            echo "Attempt $i/5 to run test targets"
-            bazel test --keep_going --remote_http_cache=$BAZEL_REMOTE_CACHE_URL --google_credentials=./config/oppia-dev-workflow-remote-cache-credentials.json -- $BAZEL_TEST_TARGETS
-          done
-          # Capture the error code of the final command run (which should be a success if there isn't a real build failure).
-          last_error_code=$?
-          # Reenable exit-on-first-failure.
-          set -e
-          # Exit only if the most recent exit was a failure (by using a subshell).
-          (exit $last_error_code)
-      - name: Run Oppia Tests (without caching, or on a fork)
-        if: ${{ env.ENABLE_CACHING == 'false' || ((github.ref != 'refs/heads/develop' || github.event_name != 'push') && (github.event.pull_request.head.repo.full_name != 'oppia/oppia-android')) }}
+
+      - name: Run Oppia Tests
         env:
           BAZEL_TEST_TARGETS: ${{ env.BAZEL_TEST_TARGETS }}
         run: |

BUILD.bazel

@@ -1,11 +1,7 @@
 # TODO(#1532): Rename file to 'BUILD' post-Gradle.
 
 load("@dagger//:workspace_defs.bzl", "dagger_rules")
-load("//:build_flavors.bzl", "AVAILABLE_FLAVORS", "define_oppia_aab_binary_flavor", "transform_android_manifest")
-load("//:version.bzl", "MAJOR_VERSION", "MINOR_VERSION", "OPPIA_DEV_KITKAT_VERSION_CODE", "OPPIA_DEV_VERSION_CODE")
-
-# This is exported here since config/ isn't a Bazel package.
-exports_files(["config/kitkat_main_dex_class_list.txt"])
+load("//:build_flavors.bzl", "AVAILABLE_FLAVORS", "define_oppia_aab_binary_flavor")
 
 # Corresponds to being accessible to all Oppia targets. This should be used for production APIs &
 # modules that may be used both in production targets and in tests.
@@ -73,63 +69,6 @@ package_group(
 )
 
 # TODO(#1640): Move binary manifest to top-level package post-Gradle.
-[
-    transform_android_manifest(
-        name = "oppia_apk_%s_transformed_manifest" % apk_flavor_metadata["flavor"],
-        application_relative_qualified_class = ".app.application.dev.DeveloperOppiaApplication",
-        build_flavor = apk_flavor_metadata["flavor"],
-        input_file = "//app:src/main/AndroidManifest.xml",
-        major_version = MAJOR_VERSION,
-        minor_version = MINOR_VERSION,
-        output_file = "AndroidManifest_transformed_%s.xml" % apk_flavor_metadata["flavor"],
-        version_code = apk_flavor_metadata["version_code"],
-    )
-    for apk_flavor_metadata in [
-        {
-            "flavor": "oppia",
-            "version_code": OPPIA_DEV_VERSION_CODE,
-        },
-        {
-            "flavor": "oppia_kitkat",
-            "version_code": OPPIA_DEV_KITKAT_VERSION_CODE,
-        },
-    ]
-]
-
-[
-    android_binary(
-        name = apk_flavor_metadata["flavor"],
-        custom_package = "org.oppia.android",
-        enable_data_binding = True,
-        main_dex_list = apk_flavor_metadata.get("main_dex_list"),
-        manifest = "oppia_apk_%s_transformed_manifest" % apk_flavor_metadata["flavor"],
-        manifest_values = {
-            "applicationId": "org.oppia.android",
-            "minSdkVersion": "%d" % apk_flavor_metadata["min_sdk_version"],
-            "targetSdkVersion": "%d" % apk_flavor_metadata["target_sdk_version"],
-        },
-        multidex = apk_flavor_metadata["multidex"],
-        deps = [
-            "//app/src/main/java/org/oppia/android/app/application/dev:developer_application",
-            "//config/src/java/org/oppia/android/config:all_languages_config",
-        ],
-    )
-    for apk_flavor_metadata in [
-        {
-            "flavor": "oppia",
-            "min_sdk_version": 21,
-            "multidex": "native",
-            "target_sdk_version": 34,
-        },
-        {
-            "flavor": "oppia_kitkat",
-            "main_dex_list": "//:config/kitkat_main_dex_class_list.txt",
-            "min_sdk_version": 21,
-            "multidex": "manual_main_dex",
-            "target_sdk_version": 34,
-        },
-    ]
-]
 
 # Define all binary flavors that can be built. Note that these are AABs, not APKs, and can be
 # be installed on a local device or emulator using a 'bazel run' command like so:

app/src/main/AppAndroidManifest.xml

@@ -1,5 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.app.ui">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/DatabindingAdaptersManifest.xml

@@ -1,5 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.databinding.adapters">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/DatabindingResourcesManifest.xml

@@ -1,5 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.app.databinding">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/RecyclerviewAdaptersManifest.xml

@@ -1,5 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.app.recyclerview.adapters">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/ViewModelManifest.xml

@@ -2,6 +2,6 @@
 <!-- TODO(#1632): Remove manifest post-Gradle -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.app.vm">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/ViewModelsManifest.xml

@@ -2,6 +2,6 @@
 <!-- TODO(#1632): Remove manifest post-Gradle -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.app.view.models">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/ViewsManifest.xml

@@ -2,6 +2,6 @@
 <!-- TODO(#1632): Remove manifest post-Gradle -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.oppia.android.app.views">
-  <uses-sdk android:minSdkVersion="19"
+  <uses-sdk android:minSdkVersion="21"
     android:targetSdkVersion="34" />
 </manifest>

app/src/main/java/org/oppia/android/app/application/AbstractOppiaApplication.kt

@@ -4,7 +4,6 @@ import android.annotation.SuppressLint
 import android.app.Application
 import android.os.Build
 import androidx.appcompat.app.AppCompatActivity
-import androidx.appcompat.app.AppCompatDelegate
 import androidx.multidex.MultiDexApplication
 import androidx.work.Configuration
 import androidx.work.WorkManager
@@ -39,14 +38,6 @@ abstract class AbstractOppiaApplication(
   @SuppressLint("ObsoleteSdkInt") // Incorrect warning.
   override fun onCreate() {
     super.onCreate()
-    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
-      // Ensure vector drawables can be properly loaded on KitKat devices. Note that this can
-      // introduce memory issues, but it's an easier-to-maintain solution that replacing all image
-      // binding with custom hook-ins (especially when it comes to databinding which isn't
-      // configurable in how it loads drawables), or building a custom vector drawable->PNG pipeline
-      // in Bazel.
-      AppCompatDelegate.setCompatVectorFromResourcesEnabled(true)
-    }
     // The current WorkManager version doesn't work in SDK 31+, so disable it.
     // TODO(#4751): Re-enable WorkManager for S+.
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.S) {

app/src/main/java/org/oppia/android/app/databinding/TextViewBindingAdapters.java

@@ -45,7 +45,7 @@ public static void setProfileLastVisitedText(@NonNull TextView textView, long ti
   }
 
   // TODO(#4345): Add test for this method.
-  /** Binds an AndroidX KitKat-compatible drawable top to the specified text view. */
+  /** Binds an AndroidX drawable top to the specified text view. */
   @BindingAdapter("drawableTopCompat")
   public static void setDrawableTopCompat(
       @NonNull TextView imageView,
@@ -56,7 +56,7 @@ public static void setDrawableTopCompat(
     );
   }
 
-  /** Binds an AndroidX KitKat-compatible drawable end to the specified text view. */
+  /** Binds an AndroidX drawable end to the specified text view. */
   @BindingAdapter("drawableEndCompat")
   public static void setDrawableEndCompat(
       @NonNull TextView imageView,

app/src/test/java/org/oppia/android/app/testing/PlatformParameterIntegrationTest.kt

@@ -15,7 +15,6 @@ import androidx.work.WorkInfo
 import androidx.work.WorkManager
 import androidx.work.impl.utils.SynchronousExecutor
 import androidx.work.testing.WorkManagerTestInitHelper
-import com.google.common.base.Optional
 import com.google.common.truth.Truth.assertThat
 import dagger.Component
 import dagger.Module
@@ -310,19 +309,17 @@ class PlatformParameterIntegrationTest {
       jsonPrefixNetworkInterceptor: JsonPrefixNetworkInterceptor,
       remoteAuthNetworkInterceptor: RemoteAuthNetworkInterceptor,
       @BaseUrl baseUrl: String
-    ): Optional<Retrofit> {
+    ): Retrofit {
       val client = OkHttpClient.Builder()
         .addInterceptor(jsonPrefixNetworkInterceptor)
         .addInterceptor(remoteAuthNetworkInterceptor)
         .build()
 
-      return Optional.of(
-        Retrofit.Builder()
-          .baseUrl(baseUrl)
-          .addConverterFactory(MoshiConverterFactory.create())
-          .client(client)
-          .build()
-      )
+      return Retrofit.Builder()
+        .baseUrl(baseUrl)
+        .addConverterFactory(MoshiConverterFactory.create())
+        .client(client)
+        .build()
     }
 
     @Provides
@@ -332,9 +329,8 @@ class PlatformParameterIntegrationTest {
     @Provides
     fun provideMockPlatformParameterService(
       mockRetrofit: MockRetrofit
-    ): Optional<PlatformParameterService> {
-      val delegate = mockRetrofit.create(PlatformParameterService::class.java)
-      return Optional.of(MockPlatformParameterService(delegate))
+    ): PlatformParameterService {
+      return MockPlatformParameterService(mockRetrofit.create(PlatformParameterService::class.java))
     }
   }