Optional day night preview annotation (#793)

Adds the `@DayNightPreviews` annotation that when used on a composable will:
- Display both a day mode and night mode preview in Android Studio.
- Produce both a day and night screenshot during screenshot testing.

The usage of this new annotation is optional, all the current previews continue to work without breakages.
New code can use, when appropriate, the new `@DayNightPreviews` annotation and replace the pattern using three `LightPreview/DarkPreview/ContentToPreview` functions with:

```
@DayNightPreviews
@Composable
fun MyScreenPreview(@PreviewParameter(MyStateProvider::class) state: MyState) {
    ElementPreview {
        MyScreen(
            state = state,
        )
    }
}
```

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/preview/DayNightPreviews.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.libraries.designsystem.preview
+
+import android.content.res.Configuration
+import androidx.compose.ui.tooling.preview.Preview
+
+/**
+ * Marker for a night mode preview.
+ *
+ * Previews with such marker will be rendered in night mode during screenshot testing.
+ *
+ * NB: Length of this constant is kept to a minimum to avoid screenshot file names being too long.
+ */
+const val NIGHT_MODE_NAME = "N"
+
+/**
+ * Marker for a day mode preview.
+ *
+ * This marker is currently not used during screenshot testing, it mainly act as a counterpart to [NIGHT_MODE_NAME].
+ *
+ * NB: Length of this constant is kept to a minimum to avoid screenshot file names being too long.
+ */
+const val DAY_MODE_NAME = "D"
+
+/**
+ * Generates 2 previews of the composable it is applied to: day and night mode.
+ *
+ * NB: Content should be wrapped into [ElementPreview] to apply proper theming.
+ */
+@Preview(name = DAY_MODE_NAME)
+@Preview(name = NIGHT_MODE_NAME, uiMode = Configuration.UI_MODE_NIGHT_YES)
+annotation class DayNightPreviews

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/preview/ElementPreview.kt

@@ -17,6 +17,7 @@
 package io.element.android.libraries.designsystem.preview
 
 import androidx.compose.foundation.background
+import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
@@ -28,8 +29,8 @@ import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.unit.dp
-import io.element.android.libraries.theme.ElementTheme
 import io.element.android.libraries.designsystem.theme.components.Surface
+import io.element.android.libraries.theme.ElementTheme
 
 @Composable
 fun ElementPreviewLight(
@@ -62,29 +63,35 @@ fun ElementThemedPreview(
     vertical: Boolean = true,
     content: @Composable () -> Unit,
 ) {
-    Box(modifier = Modifier
+    Box(
-        .background(Color.Gray)
+        modifier = Modifier
-        .padding(4.dp)) {
+            .background(Color.Gray)
+            .padding(4.dp)
+    ) {
         if (vertical) {
             Column {
-                ElementPreviewLight(
+                ElementPreview(
+                    darkTheme = false,
                     showBackground = showBackground,
                     content = content,
                 )
                 Spacer(modifier = Modifier.height(4.dp))
-                ElementPreviewDark(
+                ElementPreview(
+                    darkTheme = true,
                     showBackground = showBackground,
                     content = content
                 )
             }
         } else {
             Row {
-                ElementPreviewLight(
+                ElementPreview(
+                    darkTheme = false,
                     showBackground = showBackground,
                     content = content,
                 )
                 Spacer(modifier = Modifier.width(4.dp))
-                ElementPreviewDark(
+                ElementPreview(
+                    darkTheme = true,
                     showBackground = showBackground,
                     content = content
                 )
@@ -95,18 +102,17 @@ fun ElementThemedPreview(
 
 @Composable
 @Suppress("ModifierMissing")
-private fun ElementPreview(
+fun ElementPreview(
-    darkTheme: Boolean,
+    darkTheme: Boolean = isSystemInDarkTheme(),
-    showBackground: Boolean,
+    showBackground: Boolean = true,
     content: @Composable () -> Unit
 ) {
     ElementTheme(darkTheme = darkTheme) {
         if (showBackground) {
             // If we have a proper contentColor applied we need a Surface instead of a Box
-            Surface { content() }
+            Surface(content = content)
         } else {
             content()
         }
     }
 }
-

tests/uitests/src/test/kotlin/io/element/android/tests/uitests/ColorTestPreview.kt

@@ -38,5 +38,7 @@ class ColorTestPreview(
         )
     }
 
+    override val name: String = showkaseBrowserColor.colorName
+
     override fun toString(): String = "Color_${showkaseBrowserColor.colorGroup}_${showkaseBrowserColor.colorName}"
 }

tests/uitests/src/test/kotlin/io/element/android/tests/uitests/ComponentTestPreview.kt

@@ -25,5 +25,7 @@ class ComponentTestPreview(
     @Composable
     override fun Content() = showkaseBrowserComponent.component()
 
+    override val name: String = showkaseBrowserComponent.componentName
+
     override fun toString(): String = showkaseBrowserComponent.componentKey
 }

tests/uitests/src/test/kotlin/io/element/android/tests/uitests/ScreenshotTest.kt

@@ -38,6 +38,7 @@ import com.airbnb.android.showkase.models.Showkase
 import com.android.ide.common.rendering.api.SessionParams
 import com.google.testing.junit.testparameterinjector.TestParameter
 import com.google.testing.junit.testparameterinjector.TestParameterInjector
+import io.element.android.libraries.designsystem.preview.NIGHT_MODE_NAME
 import io.element.android.libraries.theme.ElementTheme
 import org.junit.Rule
 import org.junit.Test
@@ -95,6 +96,10 @@ class ScreenshotTest {
                 ),
                 LocalConfiguration provides Configuration().apply {
                     setLocales(LocaleList(localeStr.toLocale()))
+                    // Dark mode previews have name "N" so their component name contains "- N"
+                    if (componentTestPreview.name.contains("- $NIGHT_MODE_NAME")){
+                        uiMode = Configuration.UI_MODE_NIGHT_YES
+                    }
                 },
                 // Needed so that UI that uses it don't crash during screenshot tests
                 LocalOnBackPressedDispatcherOwner provides object : OnBackPressedDispatcherOwner {

tests/uitests/src/test/kotlin/io/element/android/tests/uitests/TestPreview.kt

@@ -21,4 +21,6 @@ import androidx.compose.runtime.Composable
 interface TestPreview {
     @Composable
     fun Content()
+
+    val name: String
 }

tests/uitests/src/test/kotlin/io/element/android/tests/uitests/TypographyTestPreview.kt

@@ -44,5 +44,7 @@ class TypographyTestPreview(
         )
     }
 
+    override val name: String = showkaseBrowserTypography.typographyName
+
     override fun toString(): String = "Typo_${showkaseBrowserTypography.typographyGroup}_${showkaseBrowserTypography.typographyName}"
 }

tools/danger/dangerfile.js

@@ -132,7 +132,8 @@ if (allowList.includes(user)) {
 
 const previewAnnotations = [
     'androidx.compose.ui.tooling.preview.Preview',
-    'io.element.android.libraries.designsystem.preview.LargeHeightPreview'
+    'io.element.android.libraries.designsystem.preview.LargeHeightPreview',
+    'io.element.android.libraries.designsystem.preview.DayNightPreviews'
 ]
 
 const filesWithPreviews = editedFiles.filter(file => file.endsWith(".kt")).filter(file => {