KT-6834 Optimize Imports: do not modify file if import list had not change

#KT-6834 Fixed

idea/src/org/jetbrains/kotlin/idea/imports/KotlinImportOptimizer.kt

@@ -151,7 +151,8 @@ public class KotlinImportOptimizer() : ImportOptimizer {
 
             val sortedImportsToGenerate = importsToGenerate.sortBy(importInsertHelper.importSortComparator)
 
-            //TODO: do not touch file if everything is already correct?
+            // check if no changes to imports required
+            if (oldImports.size() == sortedImportsToGenerate.size() && oldImports.map { it.getImportPath() } == sortedImportsToGenerate) return
 
             ApplicationManager.getApplication()!!.runWriteAction(Runnable {
                 val importList = file.getImportList()!!

idea/testData/editor/optimizeImports/DoNotTouchIfNoChanges.kt

@@ -0,0 +1,5 @@
+import java.util.ArrayList
+// some comment
+import java.util.HashSet
+
+val v: HashSet<ArrayList<String>>

idea/testData/editor/optimizeImports/DoNotTouchIfNoChanges.kt.after

@@ -0,0 +1,5 @@
+import java.util.ArrayList
+// some comment
+import java.util.HashSet
+
+val v: HashSet<ArrayList<String>>

idea/tests/org/jetbrains/kotlin/idea/imports/OptimizeImportsTestGenerated.java

@@ -81,6 +81,12 @@ public class OptimizeImportsTestGenerated extends AbstractOptimizeImportsTest {
         doTest(fileName);
     }
 
+    @TestMetadata("DoNotTouchIfNoChanges.kt")
+    public void testDoNotTouchIfNoChanges() throws Exception {
+        String fileName = JetTestUtils.navigationMetadata("idea/testData/editor/optimizeImports/DoNotTouchIfNoChanges.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("DuplicatedImports.kt")
     public void testDuplicatedImports() throws Exception {
         String fileName = JetTestUtils.navigationMetadata("idea/testData/editor/optimizeImports/DuplicatedImports.kt");