Unused symbol: handle imports from nested objects correctly

So #KT-17437 Fixed

idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt

@@ -252,8 +252,8 @@ class UnusedSymbolInspection : AbstractKotlinInspection() {
                 if (import.aliasName != null && import.aliasName != declaration.name) {
                     return false
                 }
-                // check if we import member(s) from object or enum and search for their usages
-                if (declaration is KtObjectDeclaration || (declaration is KtClass && declaration.isEnum())) {
+                // check if we import member(s) from object / nested object / enum and search for their usages
+                if (declaration is KtClassOrObject) {
                     if (import.isAllUnder) {
                         val importedFrom = import.importedReference?.getQualifiedElementSelector()?.mainReference?.resolve()
                                                    as? KtClassOrObject ?: return true
@@ -264,7 +264,11 @@ class UnusedSymbolInspection : AbstractKotlinInspection() {
                             val importedDeclaration =
                                     import.importedReference?.getQualifiedElementSelector()?.mainReference?.resolve() as? KtNamedDeclaration
                                     ?: return true
-                            return declaration !in importedDeclaration.parentsWithSelf && !hasNonTrivialUsages(importedDeclaration)
+                            if (declaration is KtObjectDeclaration ||
+                                (declaration is KtClass && declaration.isEnum()) ||
+                                importedDeclaration.containingClassOrObject is KtObjectDeclaration) {
+                                return declaration !in importedDeclaration.parentsWithSelf && !hasNonTrivialUsages(importedDeclaration)
+                            }
                         }
                     }
                 }

idea/testData/inspectionsLocal/unusedSymbol/companionViaImport.kt

@@ -0,0 +1,14 @@
+// PROBLEM: none
+
+import My.Companion.create
+
+class <caret>My {
+    companion object {
+        fun create() = My()
+    }
+}
+
+fun test() {
+    val my = create()
+    my.hashCode()
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -1850,6 +1850,12 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/testData/inspectionsLocal/unusedSymbol"), Pattern.compile("^([\\w\\-_]+)\\.kt$"), TargetBackend.ANY, true);
         }
 
+        @TestMetadata("companionViaImport.kt")
+        public void testCompanionViaImport() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/unusedSymbol/companionViaImport.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("inAnonymous.kt")
         public void testInAnonymous() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/inspectionsLocal/unusedSymbol/inAnonymous.kt");