Use applicationContext for Singleton Image Loader

coil/src/androidMain/kotlin/coil3/SingletonImageLoader.android.kt

@@ -3,3 +3,16 @@ package coil3
 internal actual fun PlatformContext.applicationImageLoaderFactory(): SingletonImageLoader.Factory? {
     return applicationContext as? SingletonImageLoader.Factory
 }
+
+/**
+ * Converts PlatformContext to ApplicationContext if possible.
+ * Otherwise returns the platform context as is.
+ * @return PlatformContext's applicationContext for Android.
+ */
+internal actual fun PlatformContext.toApplicationContext(): PlatformContext =
+    try {
+        this.applicationContext as PlatformContext
+    } catch (exception: Exception) {
+        // Return the platform context as is just in case.
+        this
+    }

coil/src/androidUnitTest/kotlin/coil3/SingletonImageLoaderAndroidTest.kt

@@ -2,7 +2,10 @@ package coil3
 
 import android.app.Application
 import coil3.test.utils.RobolectricTest
+import coil3.test.utils.ViewTestActivity
 import coil3.test.utils.context
+import coil3.test.utils.launchActivity
+import kotlin.test.assertEquals
 import kotlin.test.assertFalse
 import kotlin.test.assertSame
 import kotlin.test.assertTrue
@@ -47,6 +50,31 @@ class SingletonImageLoaderAndroidTest : RobolectricTest() {
         assertTrue(factory.isInitialized)
         assertFalse((context.applicationContext as TestApplication).isInitialized)
     }
+
+    @Test
+    @Config(application = TestApplication::class)
+    fun `GIVEN activity context, WHEN image loader is set, THEN it uses application context`() {
+        // GIVEN
+        var capturedContext: PlatformContext? = null
+        val factory = SingletonImageLoader.Factory { ctx ->
+            capturedContext = ctx
+            ImageLoader(context = capturedContext)
+        }
+
+        SingletonImageLoader.setSafe(factory)
+
+        // WHEN
+        launchActivity { activity: ViewTestActivity ->
+            SingletonImageLoader.get(activity)
+        }
+
+        // THEN
+        assertEquals(
+            expected = context.applicationContext,
+            actual = capturedContext,
+            message = "Expected factory to receive Application context, not Activity"
+        )
+    }
 }
 
 class TestApplication : Application(), SingletonImageLoader.Factory {

coil/src/commonMain/kotlin/coil3/SingletonImageLoader.kt

@@ -86,15 +86,18 @@ object SingletonImageLoader {
     private fun newImageLoader(context: PlatformContext): ImageLoader {
         // Local storage to ensure newImageLoader is invoked at most once.
         var imageLoader: ImageLoader? = null
+        // No impact on non-Android platforms, still uses
+        // same context, but for Android it uses applicationContext when possible.
+        val applicationContext = context.toApplicationContext()
 
         return reference.updateAndGet { value ->
             when {
                 value is ImageLoader -> value
                 imageLoader != null -> imageLoader
                 else -> {
-                    ((value as? Factory)?.newImageLoader(context)
-                        ?: context.applicationImageLoaderFactory()?.newImageLoader(context)
-                        ?: DefaultSingletonImageLoaderFactory.newImageLoader(context))
+                    ((value as? Factory)?.newImageLoader(applicationContext)
+                        ?: applicationContext.applicationImageLoaderFactory()?.newImageLoader(applicationContext)
+                        ?: DefaultSingletonImageLoaderFactory.newImageLoader(applicationContext))
                         .also { imageLoader = it }
                 }
             }
@@ -115,6 +118,8 @@ object SingletonImageLoader {
     }
 }
 
+internal expect fun PlatformContext.toApplicationContext(): PlatformContext
+
 internal expect fun PlatformContext.applicationImageLoaderFactory(): Factory?
 
 private val DefaultSingletonImageLoaderFactory = Factory { context ->

coil/src/nonAndroidMain/kotlin/coil3/SingletonImageLoader.nonAndroid.kt

@@ -3,3 +3,8 @@ package coil3
 internal actual fun PlatformContext.applicationImageLoaderFactory(): SingletonImageLoader.Factory? {
     return null
 }
+
+/**
+ * @return the PlatformContext as is, for non-Android platform.
+ */
+internal actual fun PlatformContext.toApplicationContext(): PlatformContext = this