Improve search for facade light class by kotlin file

LightClassUtil#getWrappingClass works for clashing facade fq names

 #KT-17855 Fixed

compiler/light-classes/src/org/jetbrains/kotlin/asJava/LightClassUtil.kt

@@ -153,9 +153,7 @@ object LightClassUtil {
 
         if (parent is KtFile) {
             // top-level declaration
-            val fqName = parent.javaFileFacadeFqName
-            val project = declaration.project
-            return JavaElementFinder.getInstance(project).findClass(fqName.asString(), GlobalSearchScope.allScope(project))
+            return findFileFacade(parent)
         }
         else if (parent is KtClassBody) {
             assert(parent.parent is KtClassOrObject)
@@ -165,6 +163,17 @@ object LightClassUtil {
         return null
     }
 
+    private fun findFileFacade(ktFile: KtFile): PsiClass? {
+        val fqName = ktFile.javaFileFacadeFqName
+        val project = ktFile.project
+        val classesWithMatchingFqName = JavaElementFinder.getInstance(project).findClasses(fqName.asString(), GlobalSearchScope.allScope(project))
+        return classesWithMatchingFqName.singleOrNull() ?:
+               classesWithMatchingFqName.find {
+                   // NOTE: for multipart facades this works via FakeLightClassForFileOfPackage
+                   it.containingFile?.virtualFile == ktFile.virtualFile
+               }
+    }
+
     private fun getWrappingClasses(declaration: KtDeclaration): Sequence<PsiClass> {
         val wrapperClass = getWrappingClass(declaration) ?: return emptySequence()
         val wrapperClassOrigin = (wrapperClass as KtLightClass).kotlinOrigin

idea/testData/multiFileInspections/mainInTwoModules/before/A/src/part1A.kt

@@ -0,0 +1,8 @@
+@file:JvmName("MultiPart")
+@file:JvmMultifileClass
+
+package test.multiPart
+
+fun main(args: Array<String>) {
+
+}

idea/testData/multiFileInspections/mainInTwoModules/before/A/src/part2A.kt

@@ -0,0 +1,9 @@
+@file:JvmName("MultiPart")
+@file:JvmMultifileClass
+
+package test.multiPart
+
+fun other() {
+
+}
+

idea/testData/multiFileInspections/mainInTwoModules/before/A/src/simpleMain.kt

@@ -1,3 +1,5 @@
+package simple
+
 fun main(args: Array<String>) {
 
 }

idea/testData/multiFileInspections/mainInTwoModules/before/B/src/part1B.kt

@@ -0,0 +1,8 @@
+@file:JvmName("MultiPart")
+@file:JvmMultifileClass
+
+package test.multiPart
+
+fun other() {
+
+}

idea/testData/multiFileInspections/mainInTwoModules/before/B/src/part2B.kt

@@ -0,0 +1,8 @@
+@file:JvmName("MultiPart")
+@file:JvmMultifileClass
+
+package test.multiPart
+
+fun main(args: Array<String>) {
+
+}

idea/testData/multiFileInspections/mainInTwoModules/before/B/src/simpleMain.kt

@@ -1,3 +1,5 @@
+package simple
+
 fun main(args: Array<String>) {
 
 }

idea/testData/multiFileInspections/mainInTwoModules/expected.xml

@@ -1,3 +1,17 @@
 <problems>
+    <problem>
+        <file>part2A.kt</file>
+        <line>6</line>
+        <entry_point TYPE="file" FQNAME="part2A.kt" />
+        <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused symbol</problem_class>
+        <description>Function ''other'' is never used</description>
+    </problem>
 
+    <problem>
+        <file>part1B.kt</file>
+        <line>6</line>
+        <entry_point TYPE="file" FQNAME="part1B.kt" />
+        <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Unused symbol</problem_class>
+        <description>Function ''other'' is never used</description>
+    </problem>
 </problems>