[Commonizer] Implement SingleTargetPropagationTest to cover KT-46248

^KT-46248

native/commonizer/tests/org/jetbrains/kotlin/commonizer/AbstractInlineSourcesCommonizationTest.kt

@@ -160,8 +160,8 @@ abstract class AbstractInlineSourcesCommonizationTest : KtInlineSourceCommonizer
                 if (dependencies.isEmpty()) null
                 else MockModulesProvider.create(dependencies)
             },
-            targetProviders = TargetDependent(targets.map { it.target }) { commonizerTarget ->
+            targetProviders = TargetDependent(outputTarget.allLeaves()) { commonizerTarget ->
-                val target = targets.single { it.target == commonizerTarget }
+                val target = targets.singleOrNull { it.target == commonizerTarget } ?: return@TargetDependent null
                 TargetProvider(
                     target = commonizerTarget,
                     modulesProvider = MockModulesProvider.create(target.modules.map { createModuleDescriptor(it) })

native/commonizer/tests/org/jetbrains/kotlin/commonizer/hierarchical/SingleTargetPropagationTest.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.commonizer.hierarchical
+
+import org.jetbrains.kotlin.commonizer.AbstractInlineSourcesCommonizationTest
+import org.jetbrains.kotlin.commonizer.assertCommonized
+import org.junit.Test
+
+/**
+ * Related https://youtrack.jetbrains.com/issue/KT-46248
+ */
+class SingleTargetPropagationTest : AbstractInlineSourcesCommonizationTest() {
+
+    /**
+     * Following the simple design principle:
+     * Absent/Unsupported targets shall result in the same output as a request only mentioning supported targets
+     */
+    @Test
+    fun `test single native target in hierarchy`() {
+        val result = commonize {
+            outputTarget("((a, b), (c, d))")
+            simpleSingleSourceTarget("a", """class A""")
+        }
+
+        result.assertCommonized("a", "class A")
+        result.assertCommonized("(a,b)", "expect class A expect constructor()")
+        result.assertCommonized("((a, b), (c, d))", "expect class A expect constructor()")
+    }
+}