Discriminate header classes in favor of non-header type aliases

In the test case, the problem was that Foo.a's type was resolved to the
_class A_, which was written to metadata on JVM instead of the class
AImpl with typealias A as an abbreviation. This metadata was incorrect
because there's no class A from the JVM compiler's point of view; that's
why the error "cannot access class A" was reported

 #KT-19151 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/AbstractLazyMemberScope.kt

@@ -69,13 +69,17 @@ protected constructor(
         // NB we should resolve type alias descriptors even if a class descriptor with corresponding name is present
         val classes = classDescriptors(name)
         val typeAliases = typeAliasDescriptors(name)
-        var resultingClass: ClassDescriptor? = null
+        // See getFirstClassifierDiscriminateHeaders()
+        var result: ClassifierDescriptor? = null
         for (klass in classes) {
-            // See getFirstClassifierDiscriminateHeaders()
             if (!klass.isHeader) return klass
-            if (resultingClass == null) resultingClass = klass
+            if (result == null) result = klass
         }
-        return resultingClass ?: typeAliases.firstOrNull()
+        for (typeAlias in typeAliases) {
+            if (!typeAlias.isHeader) return typeAlias
+            if (result == null) result = typeAlias
+        }
+        return result
     }
 
     override fun getContributedFunctions(name: Name, location: LookupLocation): Collection<SimpleFunctionDescriptor> {

compiler/testData/multiplatform/implTypeAlias/discriminateHeaderClassInFavorOfTypeAlias/common.kt

@@ -0,0 +1,3 @@
+class Foo(val a: A? = null)
+
+header class A

compiler/testData/multiplatform/implTypeAlias/discriminateHeaderClassInFavorOfTypeAlias/jvm.kt

@@ -0,0 +1,5 @@
+impl typealias A = AImpl
+
+class AImpl {
+    fun jvm(): A = this
+}

compiler/testData/multiplatform/implTypeAlias/discriminateHeaderClassInFavorOfTypeAlias/jvm2.kt

@@ -0,0 +1 @@
+val a = Foo().a?.jvm()

compiler/testData/multiplatform/implTypeAlias/discriminateHeaderClassInFavorOfTypeAlias/output.txt

@@ -0,0 +1,11 @@
+-- Common --
+Exit code: OK
+Output:
+
+-- JVM --
+Exit code: OK
+Output:
+
+-- JVM (2) --
+Exit code: OK
+Output:

compiler/tests/org/jetbrains/kotlin/multiplatform/MultiPlatformIntegrationTestGenerated.java

@@ -155,6 +155,12 @@ public class MultiPlatformIntegrationTestGenerated extends AbstractMultiPlatform
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/multiplatform/implTypeAlias"), Pattern.compile("^([^\\.]+)$"), TargetBackend.ANY, true);
         }
 
+        @TestMetadata("discriminateHeaderClassInFavorOfTypeAlias")
+        public void testDiscriminateHeaderClassInFavorOfTypeAlias() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/multiplatform/implTypeAlias/discriminateHeaderClassInFavorOfTypeAlias/");
+            doTest(fileName);
+        }
+
         @TestMetadata("generic")
         public void testGeneric() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/multiplatform/implTypeAlias/generic/");