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

@@ -90,7 +90,7 @@ 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

@@ -90,9 +90,7 @@ 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

@@ -97,9 +97,7 @@ fun NiaApp(
 ) {
     val shouldShowGradientBackground =
         appState.currentTopLevelDestination == TopLevelDestination.FOR_YOU
-    var showSettingsDialog by rememberSaveable {
-        mutableStateOf(false)
-    }
+    var showSettingsDialog by rememberSaveable { mutableStateOf(false) }
 
     NiaBackground {
         NiaGradientBackground(

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

@@ -164,9 +164,7 @@ 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

@@ -91,11 +91,10 @@ 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
@@ -105,7 +104,7 @@ private fun <T> List<T>.matchIds(
     idGetter: (T) -> String,
 ) = when (ids) {
     null -> this
-    else -> ids.toSet().let { idSet -> this.filter { idSet.contains(idGetter(it)) } }
+    else -> ids.toSet().let { idSet -> filter { idGetter(it) in idSet } }
 }
 
 /**

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
 }

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

@@ -103,9 +103,7 @@ class NiaPreferencesDataSource @Inject constructor(
 
     suspend fun setDynamicColorPreference(useDynamicColor: Boolean) {
         userPreferences.updateData {
-            it.copy {
-                this.useDynamicColor = useDynamicColor
-            }
+            it.copy { this.useDynamicColor = useDynamicColor }
         }
     }
 
@@ -190,9 +188,7 @@ class NiaPreferencesDataSource @Inject constructor(
 
     suspend fun setShouldHideOnboarding(shouldHideOnboarding: Boolean) {
         userPreferences.updateData {
-            it.copy {
-                this.shouldHideOnboarding = shouldHideOnboarding
-            }
+            it.copy { this.shouldHideOnboarding = shouldHideOnboarding }
         }
     }
 }

core/designsystem/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/core/designsystem/ThemeTest.kt

@@ -16,7 +16,8 @@
 
 package com.google.samples.apps.nowinandroid.core.designsystem
 
-import android.os.Build
+import android.os.Build.VERSION.SDK_INT
+import android.os.Build.VERSION_CODES
 import androidx.compose.material3.ColorScheme
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.dynamicDarkColorScheme
@@ -219,60 +220,41 @@ class ThemeTest {
     }
 
     @Composable
-    private fun dynamicLightColorSchemeWithFallback(): ColorScheme {
-        return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
-            dynamicLightColorScheme(LocalContext.current)
-        } else {
-            LightDefaultColorScheme
-        }
+    private fun dynamicLightColorSchemeWithFallback(): ColorScheme = when {
+        SDK_INT >= VERSION_CODES.S -> dynamicLightColorScheme(LocalContext.current)
+        else -> LightDefaultColorScheme
     }
 
     @Composable
-    private fun dynamicDarkColorSchemeWithFallback(): ColorScheme {
-        return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
-            dynamicDarkColorScheme(LocalContext.current)
-        } else {
-            DarkDefaultColorScheme
-        }
+    private fun dynamicDarkColorSchemeWithFallback(): ColorScheme = when {
+        SDK_INT >= VERSION_CODES.S -> dynamicDarkColorScheme(LocalContext.current)
+        else -> DarkDefaultColorScheme
     }
 
-    private fun emptyGradientColors(colorScheme: ColorScheme): GradientColors {
-        return GradientColors(container = colorScheme.surfaceColorAtElevation(2.dp))
-    }
+    private fun emptyGradientColors(colorScheme: ColorScheme): GradientColors =
+        GradientColors(container = colorScheme.surfaceColorAtElevation(2.dp))
 
-    private fun defaultGradientColors(colorScheme: ColorScheme): GradientColors {
-        return GradientColors(
-            top = colorScheme.inverseOnSurface,
-            bottom = colorScheme.primaryContainer,
-            container = colorScheme.surface,
-        )
-    }
+    private fun defaultGradientColors(colorScheme: ColorScheme): GradientColors = GradientColors(
+        top = colorScheme.inverseOnSurface,
+        bottom = colorScheme.primaryContainer,
+        container = colorScheme.surface,
+    )
 
-    private fun dynamicGradientColorsWithFallback(colorScheme: ColorScheme): GradientColors {
-        return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
-            emptyGradientColors(colorScheme)
-        } else {
-            defaultGradientColors(colorScheme)
-        }
+    private fun dynamicGradientColorsWithFallback(colorScheme: ColorScheme): GradientColors = when {
+        SDK_INT >= VERSION_CODES.S -> emptyGradientColors(colorScheme)
+        else -> defaultGradientColors(colorScheme)
     }
 
-    private fun defaultBackgroundTheme(colorScheme: ColorScheme): BackgroundTheme {
-        return BackgroundTheme(
-            color = colorScheme.surface,
-            tonalElevation = 2.dp,
-        )
-    }
+    private fun defaultBackgroundTheme(colorScheme: ColorScheme): BackgroundTheme = BackgroundTheme(
+        color = colorScheme.surface,
+        tonalElevation = 2.dp,
+    )
 
-    private fun defaultTintTheme(): TintTheme {
-        return TintTheme()
-    }
+    private fun defaultTintTheme(): TintTheme = TintTheme()
 
-    private fun dynamicTintThemeWithFallback(colorScheme: ColorScheme): TintTheme {
-        return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
-            TintTheme(colorScheme.primary)
-        } else {
-            TintTheme()
-        }
+    private fun dynamicTintThemeWithFallback(colorScheme: ColorScheme): TintTheme = when {
+        SDK_INT >= VERSION_CODES.S -> TintTheme(colorScheme.primary)
+        else -> TintTheme()
     }
 
     /**

core/designsystem/src/main/kotlin/com/google/samples/apps/nowinandroid/core/designsystem/component/DynamicAsyncImage.kt

@@ -28,6 +28,7 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color.Companion.Unspecified
 import androidx.compose.ui.graphics.ColorFilter
 import androidx.compose.ui.graphics.painter.Painter
 import androidx.compose.ui.layout.ContentScale
@@ -79,7 +80,7 @@ fun DynamicAsyncImage(
             contentScale = ContentScale.Crop,
             painter = if (isError.not() && !isLocalInspection) imageLoader else placeholder,
             contentDescription = contentDescription,
-            colorFilter = if (iconTint != null) ColorFilter.tint(iconTint) else null,
+            colorFilter = if (iconTint != Unspecified) ColorFilter.tint(iconTint) else null,
         )
     }
 }

core/designsystem/src/main/kotlin/com/google/samples/apps/nowinandroid/core/designsystem/component/TopAppBar.kt

@@ -40,9 +40,9 @@ import com.google.samples.apps.nowinandroid.core.designsystem.icon.NiaIcons
 fun NiaTopAppBar(
     @StringRes titleRes: Int,
     navigationIcon: ImageVector,
-    navigationIconContentDescription: String?,
+    navigationIconContentDescription: String,
     actionIcon: ImageVector,
-    actionIconContentDescription: String?,
+    actionIconContentDescription: String,
     modifier: Modifier = Modifier,
     colors: TopAppBarColors = TopAppBarDefaults.centerAlignedTopAppBarColors(),
     onNavigationClick: () -> Unit = {},

core/designsystem/src/main/kotlin/com/google/samples/apps/nowinandroid/core/designsystem/component/scrollbar/ScrollbarExt.kt

@@ -229,10 +229,5 @@ fun LazyStaggeredGridState.scrollbarState(
         .collect { value = it }
 }.value
 
-private inline fun <T> List<T>.floatSumOf(selector: (T) -> Float): Float {
-    var sum = 0f
-    for (element in this) {
-        sum += selector(element)
-    }
-    return sum
-}
+private inline fun <T> List<T>.floatSumOf(selector: (T) -> Float): Float =
+    fold(0f) { acc, it -> acc + selector(it) }

core/designsystem/src/main/kotlin/com/google/samples/apps/nowinandroid/core/designsystem/theme/Tint.kt

@@ -25,7 +25,7 @@ import androidx.compose.ui.graphics.Color
  */
 @Immutable
 data class TintTheme(
-    val iconTint: Color? = null,
+    val iconTint: Color = Color.Unspecified,
 )
 
 /**

core/domain/src/main/kotlin/com/google/samples/apps/nowinandroid/core/domain/GetFollowableTopicsUseCase.kt

@@ -37,22 +37,20 @@ class GetFollowableTopicsUseCase @Inject constructor(
      *
      * @param sortBy - the field used to sort the topics. Default NONE = no sorting.
      */
-    operator fun invoke(sortBy: TopicSortField = NONE): Flow<List<FollowableTopic>> {
-        return combine(
-            userDataRepository.userData,
-            topicsRepository.getTopics(),
-        ) { userData, topics ->
-            val followedTopics = topics
-                .map { topic ->
-                    FollowableTopic(
-                        topic = topic,
-                        isFollowed = topic.id in userData.followedTopics,
-                    )
-                }
-            when (sortBy) {
-                NAME -> followedTopics.sortedBy { it.topic.name }
-                else -> followedTopics
+    operator fun invoke(sortBy: TopicSortField = NONE): Flow<List<FollowableTopic>> = combine(
+        userDataRepository.userData,
+        topicsRepository.getTopics(),
+    ) { userData, topics ->
+        val followedTopics = topics
+            .map { topic ->
+                FollowableTopic(
+                    topic = topic,
+                    isFollowed = topic.id in userData.followedTopics,
+                )
             }
+        when (sortBy) {
+            NAME -> followedTopics.sortedBy { it.topic.name }
+            else -> followedTopics
         }
     }
 }

core/model/src/main/kotlin/com/google/samples/apps/nowinandroid/core/model/data/UserNewsResource.kt

@@ -45,14 +45,13 @@ data class UserNewsResource internal constructor(
         followableTopics = newsResource.topics.map { topic ->
             FollowableTopic(
                 topic = topic,
-                isFollowed = userData.followedTopics.contains(topic.id),
+                isFollowed = topic.id in userData.followedTopics,
             )
         },
-        isSaved = userData.bookmarkedNewsResources.contains(newsResource.id),
-        hasBeenViewed = userData.viewedNewsResources.contains(newsResource.id),
+        isSaved = newsResource.id in userData.bookmarkedNewsResources,
+        hasBeenViewed = newsResource.id in userData.viewedNewsResources,
     )
 }
 
-fun List<NewsResource>.mapToUserNewsResources(userData: UserData): List<UserNewsResource> {
-    return map { UserNewsResource(it, userData) }
-}
+fun List<NewsResource>.mapToUserNewsResources(userData: UserData): List<UserNewsResource> =
+    map { UserNewsResource(it, userData) }

core/notifications/src/main/kotlin/com/google/samples/apps/nowinandroid/core/notifications/SystemTrayNotifier.kt

@@ -24,10 +24,10 @@ import android.app.PendingIntent
 import android.content.ComponentName
 import android.content.Context
 import android.content.Intent
-import android.content.pm.PackageManager
+import android.content.pm.PackageManager.PERMISSION_GRANTED
 import android.os.Build.VERSION
 import android.os.Build.VERSION_CODES
-import androidx.core.app.ActivityCompat
+import androidx.core.app.ActivityCompat.checkSelfPermission
 import androidx.core.app.NotificationCompat
 import androidx.core.app.NotificationCompat.InboxStyle
 import androidx.core.app.NotificationManagerCompat
@@ -57,30 +57,24 @@ class SystemTrayNotifier @Inject constructor(
     override fun postNewsNotifications(
         newsResources: List<NewsResource>,
     ) = with(context) {
-        if (ActivityCompat.checkSelfPermission(
-                this,
-                permission.POST_NOTIFICATIONS,
-            ) != PackageManager.PERMISSION_GRANTED
-        ) {
+        if (checkSelfPermission(this, permission.POST_NOTIFICATIONS) != PERMISSION_GRANTED) {
             return
         }
 
-        val truncatedNewsResources = newsResources
-            .take(MAX_NUM_NOTIFICATIONS)
+        val truncatedNewsResources = newsResources.take(MAX_NUM_NOTIFICATIONS)
 
-        val newsNotifications = truncatedNewsResources
-            .map { newsResource ->
-                createNewsNotification {
-                    setSmallIcon(
-                        com.google.samples.apps.nowinandroid.core.common.R.drawable.ic_nia_notification,
-                    )
-                        .setContentTitle(newsResource.title)
-                        .setContentText(newsResource.content)
-                        .setContentIntent(newsPendingIntent(newsResource))
-                        .setGroup(NEWS_NOTIFICATION_GROUP)
-                        .setAutoCancel(true)
-                }
+        val newsNotifications = truncatedNewsResources.map { newsResource ->
+            createNewsNotification {
+                setSmallIcon(
+                    com.google.samples.apps.nowinandroid.core.common.R.drawable.ic_nia_notification,
+                )
+                    .setContentTitle(newsResource.title)
+                    .setContentText(newsResource.content)
+                    .setContentIntent(newsPendingIntent(newsResource))
+                    .setGroup(NEWS_NOTIFICATION_GROUP)
+                    .setAutoCancel(true)
             }
+        }
         val summaryNotification = createNewsNotification {
             val title = getString(
                 R.string.news_notification_group_summary,
@@ -117,9 +111,7 @@ class SystemTrayNotifier @Inject constructor(
         newsResources: List<NewsResource>,
         title: String,
     ): InboxStyle = newsResources
-        .fold(InboxStyle()) { inboxStyle, newsResource ->
-            inboxStyle.addLine(newsResource.title)
-        }
+        .fold(InboxStyle()) { inboxStyle, newsResource -> inboxStyle.addLine(newsResource.title) }
         .setBigContentTitle(title)
         .setSummaryText(title)
 }

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/NiaTestRunner.kt

@@ -25,7 +25,6 @@ import dagger.hilt.android.testing.HiltTestApplication
  * A custom runner to set up the instrumented application class for tests.
  */
 class NiaTestRunner : AndroidJUnitRunner() {
-    override fun newApplication(cl: ClassLoader?, name: String?, context: Context?): Application {
-        return super.newApplication(cl, HiltTestApplication::class.java.name, context)
-    }
+    override fun newApplication(cl: ClassLoader, name: String, context: Context): Application =
+        super.newApplication(cl, HiltTestApplication::class.java.name, context)
 }

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/repository/TestNewsRepository.kt

@@ -43,9 +43,7 @@ class TestNewsRepository : NewsRepository {
                 }
             }
             query.filterNewsIds?.let { filterNewsIds ->
-                result = newsResources.filter {
-                    filterNewsIds.contains(it.id)
-                }
+                result = newsResources.filter { it.id in filterNewsIds }
             }
             result
         }

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/repository/TestRecentSearchRepository.kt

@@ -32,7 +32,5 @@ class TestRecentSearchRepository : RecentSearchRepository {
         cachedRecentSearches.add(RecentSearchQuery(searchQuery))
     }
 
-    override suspend fun clearRecentSearches() {
-        cachedRecentSearches.clear()
-    }
+    override suspend fun clearRecentSearches() = cachedRecentSearches.clear()
 }

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/repository/TestSearchContentsRepository.kt

@@ -29,18 +29,15 @@ class TestSearchContentsRepository : SearchContentsRepository {
     private val cachedTopics: MutableList<Topic> = mutableListOf()
     private val cachedNewsResources: MutableList<NewsResource> = mutableListOf()
 
-    override suspend fun populateFtsData() { /* no-op */ }
+    override suspend fun populateFtsData() = Unit
 
     override fun searchContents(searchQuery: String): Flow<SearchResult> = flowOf(
         SearchResult(
             topics = cachedTopics.filter {
-                it.name.contains(searchQuery) ||
-                    it.shortDescription.contains(searchQuery) ||
-                    it.longDescription.contains(searchQuery)
+                searchQuery in it.name || searchQuery in it.shortDescription || searchQuery in it.longDescription
             },
             newsResources = cachedNewsResources.filter {
-                it.content.contains(searchQuery) ||
-                    it.title.contains(searchQuery)
+                searchQuery in it.content || searchQuery in it.title
             },
         ),
     )

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/repository/TestTopicsRepository.kt

@@ -33,9 +33,8 @@ class TestTopicsRepository : TopicsRepository {
 
     override fun getTopics(): Flow<List<Topic>> = topicsFlow
 
-    override fun getTopic(id: String): Flow<Topic> {
-        return topicsFlow.map { topics -> topics.find { it.id == id }!! }
-    }
+    override fun getTopic(id: String): Flow<Topic> =
+        topicsFlow.map { topics -> topics.find { it.id == id }!! }
 
     /**
      * A test-only API to allow controlling the list of topics from tests.

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/util/MainDispatcherRule.kt

@@ -32,11 +32,7 @@ import org.junit.runner.Description
 class MainDispatcherRule(
     private val testDispatcher: TestDispatcher = UnconfinedTestDispatcher(),
 ) : TestWatcher() {
-    override fun starting(description: Description) {
-        Dispatchers.setMain(testDispatcher)
-    }
+    override fun starting(description: Description) = Dispatchers.setMain(testDispatcher)
 
-    override fun finished(description: Description) {
-        Dispatchers.resetMain()
-    }
+    override fun finished(description: Description) = Dispatchers.resetMain()
 }

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/util/TestAnalyticsHelper.kt

@@ -26,5 +26,5 @@ class TestAnalyticsHelper : AnalyticsHelper {
         events.add(event)
     }
 
-    fun hasLogged(event: AnalyticsEvent) = events.contains(event)
+    fun hasLogged(event: AnalyticsEvent) = event in events
 }

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/util/TestSyncManager.kt

@@ -26,9 +26,7 @@ class TestSyncManager : SyncManager {
 
     override val isSyncing: Flow<Boolean> = syncStatusFlow
 
-    override fun requestSync() {
-        TODO("Not yet implemented")
-    }
+    override fun requestSync(): Unit = TODO("Not yet implemented")
 
     /**
      * A test-only API to set the sync status from tests.

core/ui/src/main/kotlin/com/google/samples/apps/nowinandroid/core/ui/JankStatsExtensions.kt

@@ -50,7 +50,7 @@ fun rememberMetricsStateHolder(): Holder {
  */
 @Composable
 fun TrackJank(
-    vararg keys: Any?,
+    vararg keys: Any,
     reportMetric: suspend CoroutineScope.(state: Holder) -> Unit,
 ) {
     val metrics = rememberMetricsStateHolder()
@@ -65,7 +65,7 @@ fun TrackJank(
  */
 @Composable
 fun TrackDisposableJank(
-    vararg keys: Any?,
+    vararg keys: Any,
     reportMetric: DisposableEffectScope.(state: Holder) -> DisposableEffectResult,
 ) {
     val metrics = rememberMetricsStateHolder()

core/ui/src/main/kotlin/com/google/samples/apps/nowinandroid/core/ui/NewsFeed.kt

@@ -64,9 +64,7 @@ fun LazyStaggeredGridScope.newsFeed(
                 key = { it.id },
                 contentType = { "newsFeedItem" },
             ) { userNewsResource ->
-                val resourceUrl by remember {
-                    mutableStateOf(Uri.parse(userNewsResource.url))
-                }
+                val resourceUrl by remember { mutableStateOf(Uri.parse(userNewsResource.url)) }
                 val context = LocalContext.current
                 val analyticsHelper = LocalAnalyticsHelper.current
                 val backgroundColor = MaterialTheme.colorScheme.background.toArgb()

feature/bookmarks/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/BookmarksScreen.kt

@@ -47,6 +47,7 @@ import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.ColorFilter
 import androidx.compose.ui.platform.LocalLifecycleOwner
 import androidx.compose.ui.platform.testTag
@@ -237,7 +238,7 @@ private fun EmptyState(modifier: Modifier = Modifier) {
         Image(
             modifier = Modifier.fillMaxWidth(),
             painter = painterResource(id = R.drawable.img_empty_bookmarks),
-            colorFilter = if (iconTint != null) ColorFilter.tint(iconTint) else null,
+            colorFilter = if (iconTint != Color.Unspecified) ColorFilter.tint(iconTint) else null,
             contentDescription = null,
         )
 

feature/bookmarks/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/navigation/BookmarksNavigation.kt

@@ -24,7 +24,7 @@ import com.google.samples.apps.nowinandroid.feature.bookmarks.BookmarksRoute
 
 const val bookmarksRoute = "bookmarks_route"
 
-fun NavController.navigateToBookmarks(navOptions: NavOptions? = null) {
+fun NavController.navigateToBookmarks(navOptions: NavOptions) {
     this.navigate(bookmarksRoute, navOptions)
 }
 

feature/foryou/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/foryou/navigation/ForYouNavigation.kt

@@ -30,7 +30,7 @@ const val forYouNavigationRoute = "for_you_route/{$LINKED_NEWS_RESOURCE_ID}"
 private const val DEEP_LINK_URI_PATTERN =
     "https://www.nowinandroid.apps.samples.google.com/foryou/{$LINKED_NEWS_RESOURCE_ID}"
 
-fun NavController.navigateToForYou(navOptions: NavOptions? = null) {
+fun NavController.navigateToForYou(navOptions: NavOptions) {
     this.navigate(forYouNavigationRoute, navOptions)
 }
 

feature/interests/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/interests/navigation/InterestsNavigation.kt

@@ -26,7 +26,7 @@ import com.google.samples.apps.nowinandroid.feature.interests.InterestsRoute
 private const val INTERESTS_GRAPH_ROUTE_PATTERN = "interests_graph"
 const val interestsRoute = "interests_route"
 
-fun NavController.navigateToInterestsGraph(navOptions: NavOptions? = null) {
+fun NavController.navigateToInterestsGraph(navOptions: NavOptions) {
     this.navigate(INTERESTS_GRAPH_ROUTE_PATTERN, navOptions)
 }
 

feature/search/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/search/SearchScreen.kt

@@ -264,9 +264,7 @@ fun EmptySearchResultBody(
         ) { offset ->
             tryAnotherSearchString.getStringAnnotations(start = offset, end = offset)
                 .firstOrNull()
-                ?.let {
-                    onInterestsClick()
-                }
+                ?.let { onInterestsClick() }
         }
     }
 }
@@ -519,9 +517,7 @@ private fun SearchTextField(
             }
         },
         onValueChange = {
-            if (!it.contains("\n")) {
-                onSearchQueryChanged(it)
-            }
+            if ("\n" !in it) onSearchQueryChanged(it)
         },
         modifier = Modifier
             .fillMaxWidth()

feature/topic/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/TopicViewModel.kt

@@ -117,22 +117,16 @@ private fun topicUiState(
             when (followedTopicToTopicResult) {
                 is Result.Success -> {
                     val (followedTopics, topic) = followedTopicToTopicResult.data
-                    val followed = followedTopics.contains(topicId)
                     TopicUiState.Success(
                         followableTopic = FollowableTopic(
                             topic = topic,
-                            isFollowed = followed,
+                            isFollowed = topicId in followedTopics,
                         ),
                     )
                 }
 
-                is Result.Loading -> {
-                    TopicUiState.Loading
-                }
-
-                is Result.Error -> {
-                    TopicUiState.Error
-                }
+                is Result.Loading -> TopicUiState.Loading
+                is Result.Error -> TopicUiState.Error
             }
         }
 }
@@ -151,26 +145,13 @@ private fun newsUiState(
     val bookmark: Flow<Set<String>> = userDataRepository.userData
         .map { it.bookmarkedNewsResources }
 
-    return combine(
-        newsStream,
-        bookmark,
-        ::Pair,
-    )
+    return combine(newsStream, bookmark, ::Pair)
         .asResult()
         .map { newsToBookmarksResult ->
             when (newsToBookmarksResult) {
-                is Result.Success -> {
-                    val news = newsToBookmarksResult.data.first
-                    NewsUiState.Success(news)
-                }
-
-                is Result.Loading -> {
-                    NewsUiState.Loading
-                }
-
-                is Result.Error -> {
-                    NewsUiState.Error
-                }
+                is Result.Success -> NewsUiState.Success(newsToBookmarksResult.data.first)
+                is Result.Loading -> NewsUiState.Loading
+                is Result.Error -> NewsUiState.Error
             }
         }
 }

feature/topic/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/navigation/TopicNavigation.kt

@@ -40,7 +40,7 @@ internal class TopicArgs(val topicId: String) {
 
 fun NavController.navigateToTopic(topicId: String) {
     val encodedId = URLEncoder.encode(topicId, URL_CHARACTER_ENCODING)
-    this.navigate("topic_route/$encodedId") {
+    navigate("topic_route/$encodedId") {
         launchSingleTop = true
     }
 }

lint/src/main/kotlin/com/google/samples/apps/nowinandroid/lint/designsystem/DesignSystemDetector.kt

@@ -34,15 +34,13 @@ import org.jetbrains.uast.UQualifiedReferenceExpression
  */
 class DesignSystemDetector : Detector(), Detector.UastScanner {
 
-    override fun getApplicableUastTypes(): List<Class<out UElement>> {
-        return listOf(
-            UCallExpression::class.java,
-            UQualifiedReferenceExpression::class.java,
-        )
-    }
+    override fun getApplicableUastTypes(): List<Class<out UElement>> = listOf(
+        UCallExpression::class.java,
+        UQualifiedReferenceExpression::class.java,
+    )
 
-    override fun createUastHandler(context: JavaContext): UElementHandler {
-        return object : UElementHandler() {
+    override fun createUastHandler(context: JavaContext): UElementHandler =
+        object : UElementHandler() {
             override fun visitCallExpression(node: UCallExpression) {
                 val name = node.methodName ?: return
                 val preferredName = METHOD_NAMES[name] ?: return
@@ -55,7 +53,6 @@ class DesignSystemDetector : Detector(), Detector.UastScanner {
                 reportIssue(context, node, name, preferredName)
             }
         }
-    }
 
     companion object {
         @JvmField