[resources] Select default resource if there are no exact language+region or default language match (#4577)

We need to filter by language and region together because there is
slightly different logic:
1) if there is the exact match language+region then use it
2) if there is the language WITHOUT region match then use it
3) in other cases use items WITHOUT language and region qualifiers at
all

Given resources:
values
values-en-rUS
values-de

Filter results:
"en" -> values
"en-US" -> values-en-rUS
"en-GB" -> values
"de-IT" -> values-de

fixes https://github.com/JetBrains/compose-multiplatform/issues/4571

components/resources/library/src/commonMain/kotlin/org/jetbrains/compose/resources/ResourceEnvironment.kt

@@ -52,9 +52,7 @@ internal var getResourceEnvironment = ::getSystemEnvironment
 internal fun Resource.getResourceItemByEnvironment(environment: ResourceEnvironment): ResourceItem {
     //Priority of environments: https://developer.android.com/guide/topics/resources/providing-resources#table2
     items.toList()
-        .filterBy(environment.language)
-        .also { if (it.size == 1) return it.first() }
-        .filterBy(environment.region)
+        .filterByLocale(environment.language, environment.region)
         .also { if (it.size == 1) return it.first() }
         .filterBy(environment.theme)
         .also { if (it.size == 1) return it.first() }
@@ -84,4 +82,34 @@ private fun List<ResourceItem>.filterBy(qualifier: Qualifier): List<ResourceItem
     return filter { item ->
         item.qualifiers.none { it::class == qualifier::class }
     }
+}
+
+// we need to filter by language and region together because there is slightly different logic:
+// 1) if there is the exact match language+region then use it
+// 2) if there is the language WITHOUT region match then use it
+// 3) in other cases use items WITHOUT language and region qualifiers at all
+// issue: https://github.com/JetBrains/compose-multiplatform/issues/4571
+private fun List<ResourceItem>.filterByLocale(language: LanguageQualifier, region: RegionQualifier): List<ResourceItem> {
+    val withLanguage = filter { item ->
+        item.qualifiers.any { it == language }
+    }
+
+    val withExactLocale = withLanguage.filter { item ->
+        item.qualifiers.any { it == region }
+    }
+
+    //if there are the exact language + the region items
+    if (withExactLocale.isNotEmpty()) return withExactLocale
+
+    val withDefaultRegion = withLanguage.filter { item ->
+        item.qualifiers.none { it is RegionQualifier }
+    }
+
+    //if there are the language without a region items
+    if (withDefaultRegion.isNotEmpty()) return withDefaultRegion
+
+    //items without any locale qualifiers
+    return filter { item ->
+        item.qualifiers.none { it is LanguageQualifier || it is RegionQualifier }
+    }
 }

components/resources/library/src/commonTest/kotlin/org/jetbrains/compose/resources/ResourceTest.kt

@@ -30,6 +30,7 @@ class ResourceTest {
                 ResourceItem(setOf(), "default", -1, -1),
                 ResourceItem(setOf(LanguageQualifier("en")), "en", -1, -1),
                 ResourceItem(setOf(LanguageQualifier("en"), RegionQualifier("US"), XHDPI), "en-rUS-xhdpi", -1, -1),
+                ResourceItem(setOf(LanguageQualifier("de"), RegionQualifier("US")), "de-rUS", -1, -1),
                 ResourceItem(setOf(LanguageQualifier("fr"), LIGHT), "fr-light", -1, -1),
                 ResourceItem(setOf(DARK), "dark", -1, -1),
             )
@@ -48,6 +49,18 @@ class ResourceTest {
             "en",
             resource.getResourceItemByEnvironment(env("en", "IN", LIGHT, LDPI)).path
         )
+        assertEquals(
+            "de-rUS",
+            resource.getResourceItemByEnvironment(env("de", "US", LIGHT, LDPI)).path
+        )
+        assertEquals(
+            "default",
+            resource.getResourceItemByEnvironment(env("de", "", LIGHT, LDPI)).path
+        )
+        assertEquals(
+            "default",
+            resource.getResourceItemByEnvironment(env("de", "IN", LIGHT, LDPI)).path
+        )
         assertEquals(
             "default",
             resource.getResourceItemByEnvironment(env("ch", "", LIGHT, MDPI)).path