Kotlinify codebase

- Remove unnecessary nullable types
- Replace no-op  method bodies with Unit
- Convert to expression body
- Replace if with when
- Remove braces from 'when' entries
- Remove braces from if statement
- Convert to single line lambda
- oneline if/returns
- Replace 'contains' call with 'in' operator

Following this refactor, it could be great to envision a more "strict" code formatter like ktlint 1.0 (we are currently stuck at 0.48.1)

app/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/ui/NavigationTest.kt

@@ -88,7 +88,7 @@ class NavigationTest {
     lateinit var topicsRepository: TopicsRepository
 
     private fun AndroidComposeTestRule<*, *>.stringResource(@StringRes resId: Int) =
-        ReadOnlyProperty<Any?, String> { _, _ -> activity.getString(resId) }
+        ReadOnlyProperty<Any, String> { _, _ -> activity.getString(resId) }
 
     // The strings used for matching in these tests
     private val navigateUp by composeTestRule.stringResource(FeatureForyouR.string.navigate_up)

app/src/main/kotlin/com/google/samples/apps/nowinandroid/MainActivity.kt

@@ -93,9 +93,7 @@ class MainActivity : ComponentActivity() {
         lifecycleScope.launch {
             lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
                 viewModel.uiState
-                    .onEach {
-                        uiState = it
-                    }
+                    .onEach { uiState = it }
                     .collect()
             }
         }

app/src/main/kotlin/com/google/samples/apps/nowinandroid/di/JankStatsModule.kt

@@ -20,6 +20,7 @@ import android.app.Activity
 import android.util.Log
 import android.view.Window
 import androidx.metrics.performance.JankStats
+import androidx.metrics.performance.JankStats.OnFrameListener
 import dagger.Module
 import dagger.Provides
 import dagger.hilt.InstallIn
@@ -29,26 +30,20 @@ import dagger.hilt.android.components.ActivityComponent
 @InstallIn(ActivityComponent::class)
 object JankStatsModule {
     @Provides
-    fun providesOnFrameListener(): JankStats.OnFrameListener {
-        return JankStats.OnFrameListener { frameData ->
-            // Make sure to only log janky frames.
-            if (frameData.isJank) {
-                // We're currently logging this but would better report it to a backend.
-                Log.v("NiA Jank", frameData.toString())
-            }
+    fun providesOnFrameListener(): OnFrameListener = OnFrameListener { frameData ->
+        // Make sure to only log janky frames.
+        if (frameData.isJank) {
+            // We're currently logging this but would better report it to a backend.
+            Log.v("NiA Jank", frameData.toString())
         }
     }
 
     @Provides
-    fun providesWindow(activity: Activity): Window {
-        return activity.window
-    }
+    fun providesWindow(activity: Activity): Window = activity.window
 
     @Provides
     fun providesJankStats(
         window: Window,
-        frameListener: JankStats.OnFrameListener,
-    ): JankStats {
-        return JankStats.createAndTrack(window, frameListener)
-    }
+        frameListener: OnFrameListener,
+    ): JankStats = JankStats.createAndTrack(window, frameListener)
 }

app/src/main/kotlin/com/google/samples/apps/nowinandroid/ui/NiaApp.kt

@@ -79,9 +79,7 @@ fun NiaApp(
 ) {
     val shouldShowGradientBackground =
         appState.currentTopLevelDestination == TopLevelDestination.FOR_YOU
-    var showSettingsDialog by rememberSaveable {
-        mutableStateOf(false)
-    }
+    var showSettingsDialog by rememberSaveable { mutableStateOf(false) }
 
     NiaBackground {
         NiaGradientBackground(
@@ -126,7 +124,7 @@ fun NiaApp(
                     appState.topLevelDestinations.forEach { destination ->
                         val isSelected =
                             currentDestination.isTopLevelDestinationInHierarchy(destination)
-                        val isUnread = unreadDestinations.contains(destination)
+                        val isUnread = destination in unreadDestinations
                         item(
                             selected = isSelected,
                             icon = {

app/src/main/kotlin/com/google/samples/apps/nowinandroid/ui/NiaAppState.kt

@@ -139,14 +139,10 @@ class NiaAppState(
      */
     @OptIn(ExperimentalMaterial3AdaptiveNavigationSuiteApi::class)
     val navigationSuiteType: NavigationSuiteType
-        @Composable get() {
-            return if (windowSize.width > 1240.dp) {
-                NavigationSuiteType.NavigationDrawer
-            } else if (windowSize.width >= 600.dp) {
-                NavigationSuiteType.NavigationRail
-            } else {
-                NavigationSuiteType.NavigationBar
-            }
+        @Composable get() = when {
+            windowSize.width > 1240.dp -> NavigationSuiteType.NavigationDrawer
+            windowSize.width >= 600.dp -> NavigationSuiteType.NavigationRail
+            else -> NavigationSuiteType.NavigationBar
         }
 
     /**
@@ -180,9 +176,7 @@ class NiaAppState(
         }
     }
 
-    fun navigateToSearch() {
-        navController.navigateToSearch()
-    }
+    fun navigateToSearch() = navController.navigateToSearch()
 }
 
 /**

benchmarks/src/main/kotlin/androidx/test/uiautomator/UiAutomatorHelpers.kt

@@ -29,15 +29,11 @@ import androidx.test.uiautomator.HasChildrenOp.EXACTLY
 fun untilHasChildren(
     childCount: Int = 1,
     op: HasChildrenOp = AT_LEAST,
-): UiObject2Condition<Boolean> {
-    return object : UiObject2Condition<Boolean>() {
-        override fun apply(element: UiObject2): Boolean {
-            return when (op) {
-                AT_LEAST -> element.childCount >= childCount
-                EXACTLY -> element.childCount == childCount
-                AT_MOST -> element.childCount <= childCount
-            }
-        }
+): UiObject2Condition<Boolean> = object : UiObject2Condition<Boolean>() {
+    override fun apply(element: UiObject2): Boolean = when (op) {
+        AT_LEAST -> element.childCount >= childCount
+        EXACTLY -> element.childCount == childCount
+        AT_MOST -> element.childCount <= childCount
     }
 }
 

benchmarks/src/main/kotlin/com/google/samples/apps/nowinandroid/baselineprofile/StartupBaselineProfile.kt

@@ -16,6 +16,7 @@
 
 package com.google.samples.apps.nowinandroid.baselineprofile
 
+import androidx.benchmark.macro.MacrobenchmarkScope
 import androidx.benchmark.macro.junit4.BaselineProfileRule
 import com.google.samples.apps.nowinandroid.PACKAGE_NAME
 import com.google.samples.apps.nowinandroid.startActivityAndAllowNotifications
@@ -30,11 +31,9 @@ class StartupBaselineProfile {
     @get:Rule val baselineProfileRule = BaselineProfileRule()
 
     @Test
-    fun generate() =
-        baselineProfileRule.collect(
-            PACKAGE_NAME,
-            includeInStartupProfile = true,
-        ) {
-            startActivityAndAllowNotifications()
-        }
+    fun generate() = baselineProfileRule.collect(
+        PACKAGE_NAME,
+        includeInStartupProfile = true,
+        profileBlock = MacrobenchmarkScope::startActivityAndAllowNotifications,
+    )
 }

build-logic/convention/src/main/kotlin/com/google/samples/apps/nowinandroid/PrintTestApks.kt

@@ -79,14 +79,12 @@ internal abstract class PrintApkLocationTask : DefaultTask() {
     fun taskAction() {
         val hasFiles = sources.orNull?.any { directory ->
             directory.asFileTree.files.any {
-                it.isFile && it.parentFile.path.contains("build${File.separator}generated").not()
+                it.isFile && "build${File.separator}generated" !in it.parentFile.path
             }
         } ?: throw RuntimeException("Cannot check androidTest sources")
 
         // Don't print APK location if there are no androidTest source files
-        if (!hasFiles) {
-            return
-        }
+        if (!hasFiles) return
 
         val builtArtifacts = builtArtifactsLoader.get().load(apkFolder.get())
             ?: throw RuntimeException("Cannot load APKs")

core/common/src/main/kotlin/com/google/samples/apps/nowinandroid/core/result/Result.kt

@@ -23,15 +23,10 @@ import kotlinx.coroutines.flow.onStart
 
 sealed interface Result<out T> {
     data class Success<T>(val data: T) : Result<T>
-    data class Error(val exception: Throwable? = null) : Result<Nothing>
+    data class Error(val exception: Throwable) : Result<Nothing>
     data object Loading : Result<Nothing>
 }
 
-fun <T> Flow<T>.asResult(): Flow<Result<T>> {
-    return this
-        .map<T, Result<T>> {
-            Result.Success(it)
-        }
-        .onStart { emit(Result.Loading) }
-        .catch { emit(Result.Error(it)) }
-}
+fun <T> Flow<T>.asResult(): Flow<Result<T>> = map<T, Result<T>> { Result.Success(it) }
+    .onStart { emit(Result.Loading) }
+    .catch { emit(Result.Error(it)) }

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/repository/DefaultRecentSearchRepository.kt

@@ -39,9 +39,7 @@ class DefaultRecentSearchRepository @Inject constructor(
 
     override fun getRecentSearchQueries(limit: Int): Flow<List<RecentSearchQuery>> =
         recentSearchQueryDao.getRecentSearchQueryEntities(limit).map { searchQueries ->
-            searchQueries.map {
-                it.asExternalModel()
-            }
+            searchQueries.map { it.asExternalModel() }
         }
 
     override suspend fun clearRecentSearches() = recentSearchQueryDao.clearRecentSearchQueries()

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/repository/fake/FakeRecentSearchRepository.kt

@@ -26,10 +26,10 @@ import javax.inject.Inject
  * Fake implementation of the [RecentSearchRepository]
  */
 class FakeRecentSearchRepository @Inject constructor() : RecentSearchRepository {
-    override suspend fun insertOrReplaceRecentSearch(searchQuery: String) { /* no-op */ }
+    override suspend fun insertOrReplaceRecentSearch(searchQuery: String) = Unit
 
     override fun getRecentSearchQueries(limit: Int): Flow<List<RecentSearchQuery>> =
         flowOf(emptyList())
 
-    override suspend fun clearRecentSearches() { /* no-op */ }
+    override suspend fun clearRecentSearches() = Unit
 }

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/repository/fake/FakeSearchContentsRepository.kt

@@ -27,7 +27,7 @@ import javax.inject.Inject
  */
 class FakeSearchContentsRepository @Inject constructor() : SearchContentsRepository {
 
-    override suspend fun populateFtsData() { /* no-op */ }
+    override suspend fun populateFtsData() = Unit
     override fun searchContents(searchQuery: String): Flow<SearchResult> = flowOf()
     override fun getSearchContentsCount(): Flow<Int> = flowOf(1)
 }

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/repository/fake/FakeTopicsRepository.kt

@@ -55,9 +55,8 @@ class FakeTopicsRepository @Inject constructor(
         )
     }.flowOn(ioDispatcher)
 
-    override fun getTopic(id: String): Flow<Topic> {
-        return getTopics().map { it.first { topic -> topic.id == id } }
-    }
+    override fun getTopic(id: String): Flow<Topic> = getTopics()
+        .map { it.first { topic -> topic.id == id } }
 
     override suspend fun syncWith(synchronizer: Synchronizer) = true
 }

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/CompositeUserNewsResourceRepositoryTest.kt

@@ -82,7 +82,7 @@ class CompositeUserNewsResourceRepositoryTest {
         // Check that only news resources with the given topic id are returned.
         assertEquals(
             sampleNewsResources
-                .filter { it.topics.contains(sampleTopic1) }
+                .filter { sampleTopic1 in it.topics }
                 .mapToUserNewsResources(emptyUserData),
             userNewsResources.first(),
         )
@@ -104,7 +104,7 @@ class CompositeUserNewsResourceRepositoryTest {
         // Check that only news resources with the given topic id are returned.
         assertEquals(
             sampleNewsResources
-                .filter { it.topics.contains(sampleTopic1) }
+                .filter { sampleTopic1 in it.topics }
                 .mapToUserNewsResources(userData),
             userNewsResources.first(),
         )

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/UserNewsResourceTest.kt

@@ -91,14 +91,14 @@ class UserNewsResourceTest {
             // Construct the expected FollowableTopic.
             val followableTopic = FollowableTopic(
                 topic = topic,
-                isFollowed = userData.followedTopics.contains(topic.id),
+                isFollowed = topic.id in userData.followedTopics,
             )
             assertTrue(userNewsResource.followableTopics.contains(followableTopic))
         }
 
         // Check that the saved flag is set correctly.
         assertEquals(
-            userData.bookmarkedNewsResources.contains(newsResource1.id),
+            newsResource1.id in userData.bookmarkedNewsResources,
             userNewsResource.isSaved,
         )
     }

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/testdoubles/TestNewsResourceDao.kt

@@ -34,9 +34,7 @@ val nonPresentInterestsIds = setOf("2")
  */
 class TestNewsResourceDao : NewsResourceDao {
 
-    private var entitiesStateFlow = MutableStateFlow(
-        emptyList<NewsResourceEntity>(),
-    )
+    private val entitiesStateFlow = MutableStateFlow(emptyList<NewsResourceEntity>())
 
     internal var topicCrossReferences: List<NewsResourceTopicCrossRef> = listOf()
 
@@ -131,7 +129,7 @@ class TestNewsResourceDao : NewsResourceDao {
     override suspend fun deleteNewsResources(ids: List<String>) {
         val idSet = ids.toSet()
         entitiesStateFlow.update { entities ->
-            entities.filterNot { idSet.contains(it.id) }
+            entities.filterNot { it.id in idSet }
         }
     }
 }

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/testdoubles/TestNiaNetworkDataSource.kt

@@ -53,13 +53,13 @@ class TestNiaNetworkDataSource : NiaNetworkDataSource {
 
     override suspend fun getTopics(ids: List<String>?): List<NetworkTopic> =
         allTopics.matchIds(
-            ids = ids,
+            ids = ids.orEmpty(),
             idGetter = NetworkTopic::id,
         )
 
     override suspend fun getNewsResources(ids: List<String>?): List<NetworkNewsResource> =
         allNewsResources.matchIds(
-            ids = ids,
+            ids = ids.orEmpty(),
             idGetter = NetworkNewsResource::id,
         )
 
@@ -91,22 +91,18 @@ class TestNiaNetworkDataSource : NiaNetworkDataSource {
     }
 }
 
-fun List<NetworkChangeList>.after(version: Int?): List<NetworkChangeList> =
-    when (version) {
-        null -> this
-        else -> this.filter { it.changeListVersion > version }
-    }
+fun List<NetworkChangeList>.after(version: Int?): List<NetworkChangeList> = when (version) {
+    null -> this
+    else -> filter { it.changeListVersion > version }
+}
 
 /**
  * Return items from [this] whose id defined by [idGetter] is in [ids] if [ids] is not null
  */
 private fun <T> List<T>.matchIds(
-    ids: List<String>?,
+    ids: List<String>,
     idGetter: (T) -> String,
-) = when (ids) {
-    null -> this
-    else -> ids.toSet().let { idSet -> this.filter { idSet.contains(idGetter(it)) } }
-}
+) = ids.toSet().let { idSet -> filter { idGetter(it) in idSet } }
 
 /**
  * Maps items to a change list where the change list version is denoted by the index of each item.

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/testdoubles/TestTopicDao.kt

@@ -28,20 +28,15 @@ import kotlinx.coroutines.flow.update
  */
 class TestTopicDao : TopicDao {
 
-    private var entitiesStateFlow = MutableStateFlow(
-        emptyList<TopicEntity>(),
-    )
+    private val entitiesStateFlow = MutableStateFlow(emptyList<TopicEntity>())
 
-    override fun getTopicEntity(topicId: String): Flow<TopicEntity> {
+    override fun getTopicEntity(topicId: String): Flow<TopicEntity> =
         throw NotImplementedError("Unused in tests")
-    }
 
-    override fun getTopicEntities(): Flow<List<TopicEntity>> =
-        entitiesStateFlow
+    override fun getTopicEntities(): Flow<List<TopicEntity>> = entitiesStateFlow
 
     override fun getTopicEntities(ids: Set<String>): Flow<List<TopicEntity>> =
-        getTopicEntities()
-            .map { topics -> topics.filter { it.id in ids } }
+        getTopicEntities().map { topics -> topics.filter { it.id in ids } }
 
     override suspend fun getOneOffTopicEntities(): List<TopicEntity> = emptyList()
 
@@ -55,15 +50,11 @@ class TestTopicDao : TopicDao {
 
     override suspend fun upsertTopics(entities: List<TopicEntity>) {
         // Overwrite old values with new values
-        entitiesStateFlow.update { oldValues ->
-            (entities + oldValues).distinctBy(TopicEntity::id)
-        }
+        entitiesStateFlow.update { oldValues -> (entities + oldValues).distinctBy(TopicEntity::id) }
     }
 
     override suspend fun deleteTopics(ids: List<String>) {
         val idSet = ids.toSet()
-        entitiesStateFlow.update { entities ->
-            entities.filterNot { idSet.contains(it.id) }
-        }
+        entitiesStateFlow.update { entities -> entities.filterNot { it.id in idSet } }
     }
 }

core/datastore/src/main/kotlin/com/google/samples/apps/nowinandroid/core/datastore/ListToMapMigration.kt

@@ -52,7 +52,6 @@ object ListToMapMigration : DataMigration<UserPreferences> {
             hasDoneListToMapMigration = true
         }
 
-    override suspend fun shouldMigrate(currentData: UserPreferences): Boolean {
-        return !currentData.hasDoneListToMapMigration
-    }
+    override suspend fun shouldMigrate(currentData: UserPreferences): Boolean =
+        !currentData.hasDoneListToMapMigration
 }