Import: IDE should import class from root package

#KT-21422 Fixed

idea/src/org/jetbrains/kotlin/idea/actions/KotlinAddImportAction.kt

@@ -51,6 +51,7 @@ import org.jetbrains.kotlin.idea.references.resolveMainReferenceToDescriptors
 import org.jetbrains.kotlin.idea.util.ImportInsertHelper
 import org.jetbrains.kotlin.idea.util.application.executeWriteCommand
 import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.isOneSegmentFQN
 import org.jetbrains.kotlin.name.parentOrNull
 import org.jetbrains.kotlin.psi.KtElement
 import org.jetbrains.kotlin.psi.KtFile
@@ -239,18 +240,21 @@ class KotlinAddImportAction internal constructor(
                 // for class or package we use ShortenReferences because we not necessary insert an import but may want to
                 // insert partly qualified name
 
-                val importAlias = descriptor.importableFqName?.let { file.findAliasByFqName(it) }
-                if (importAlias != null || descriptor is ClassDescriptor || descriptor is PackageViewDescriptor) {
+                val importableFqName = descriptor.importableFqName
+                val importAlias = importableFqName?.let { file.findAliasByFqName(it) }
+                if (importableFqName?.isOneSegmentFQN() != true &&
+                    (importAlias != null || descriptor is ClassDescriptor || descriptor is PackageViewDescriptor)
+                ) {
                     if (element is KtSimpleNameExpression) {
                         if (importAlias != null) {
                             importAlias.nameIdentifier?.copy()?.let { element.getIdentifier()?.replace(it) }
                             val resultDescriptor = element.resolveMainReferenceToDescriptors().firstOrNull()
-                            if (descriptor.importableFqName == resultDescriptor?.importableFqName) {
+                            if (importableFqName == resultDescriptor?.importableFqName) {
                                 return@forEach
                             }
                         }
 
-                        descriptor.importableFqName?.let {
+                        importableFqName?.let {
                             element.mainReference.bindToFqName(
                                 it,
                                 KtSimpleNameReference.ShorteningMode.FORCED_SHORTENING
@@ -343,8 +347,7 @@ private class SingleImportVariant(
     val descriptors: Collection<DeclarationDescriptor>
 ) : AutoImportVariant {
     override val descriptorsToImport: Collection<DeclarationDescriptor>
-        get() =
-            listOf(descriptors.singleOrNull() ?: descriptors.sortedBy { if (it is ClassDescriptor) 0 else 1 }.first())
+        get() = listOf(descriptors.singleOrNull() ?: descriptors.minBy { if (it is ClassDescriptor) 0 else 1 }!!)
 
     override val hint: String get() = excludeFqNameCheck.asString()
 }

idea/testData/addImport/ImportFromRoot.dependency.kt

@@ -0,0 +1 @@
+class RootClass

idea/testData/addImport/ImportFromRoot.kt

@@ -0,0 +1,6 @@
+// IMPORT: class: RootClass
+package non.root.name
+
+fun test() {
+    RootClass()
+}

idea/testData/addImport/ImportFromRoot.kt.after

@@ -0,0 +1,8 @@
+// IMPORT: class: RootClass
+package non.root.name
+
+import RootClass
+
+fun test() {
+    RootClass()
+}

idea/testData/quickfix/autoImports/importFromRoot.after.kt

@@ -0,0 +1,9 @@
+// "Import" "true"
+// ERROR: Unresolved reference: RootClass
+package non.root.name
+
+import RootClass
+
+fun test() {
+    RootClass()
+}

idea/testData/quickfix/autoImports/importFromRoot.before.Dependency.kt

@@ -0,0 +1 @@
+class RootClass

idea/testData/quickfix/autoImports/importFromRoot.before.Main.kt

@@ -0,0 +1,7 @@
+// "Import" "true"
+// ERROR: Unresolved reference: RootClass
+package non.root.name
+
+fun test() {
+    RootClass<caret>()
+}

idea/tests/org/jetbrains/kotlin/addImport/AddImportTestGenerated.java

@@ -199,6 +199,11 @@ public class AddImportTestGenerated extends AbstractAddImportTest {
         runTest("idea/testData/addImport/ImportFromObject.kt");
     }
 
+    @TestMetadata("ImportFromRoot.kt")
+    public void testImportFromRoot() throws Exception {
+        runTest("idea/testData/addImport/ImportFromRoot.kt");
+    }
+
     @TestMetadata("ImportFunctionBug.kt")
     public void testImportFunctionBug() throws Exception {
         runTest("idea/testData/addImport/ImportFunctionBug.kt");

idea/tests/org/jetbrains/kotlin/idea/quickfix/QuickFixMultiFileTestGenerated.java

@@ -633,6 +633,11 @@ public class QuickFixMultiFileTestGenerated extends AbstractQuickFixMultiFileTes
             runTest("idea/testData/quickfix/autoImports/importAliasPropertyAlreadyExists.before.Main.kt");
         }
 
+        @TestMetadata("importFromRoot.before.Main.kt")
+        public void testImportFromRoot() throws Exception {
+            runTest("idea/testData/quickfix/autoImports/importFromRoot.before.Main.kt");
+        }
+
         @TestMetadata("importInFirstPartInQualifiedExpression.before.Main.kt")
         public void testImportInFirstPartInQualifiedExpression() throws Exception {
             runTest("idea/testData/quickfix/autoImports/importInFirstPartInQualifiedExpression.before.Main.kt");