Create from usage: Do not generate function body if it's declared as a trait member

#KT-6078 Fixed

idea/src/org/jetbrains/kotlin/idea/quickfix/createFromUsage/callableBuilder/CallableBuilder.kt

@@ -438,7 +438,13 @@ class CallableBuilder(val config: CallableBuilderConfiguration) {
                         else ""
 
                 val declaration : JetNamedDeclaration = when (callableInfo.kind) {
-                    CallableKind.FUNCTION -> psiFactory.createFunction("${modifiers}fun<> $header {}")
+                    CallableKind.FUNCTION -> {
+                        val body = when {
+                            containingElement is JetClass && containingElement.isTrait() && !config.isExtension -> ""
+                            else -> "{}"
+                        }
+                        psiFactory.createFunction("${modifiers}fun<> $header $body")
+                    }
                     CallableKind.CONSTRUCTOR -> {
                         with((callableInfo as ConstructorInfo).classInfo) {
                             val classBody = when (kind) {
@@ -620,6 +626,8 @@ class CallableBuilder(val config: CallableBuilderConfiguration) {
         }
 
         private fun setupFunctionBody(func: JetNamedFunction) {
+            val oldBody = func.getBodyExpression() ?: return
+
             val fileTemplate = FileTemplateManager.getInstance()!!.getCodeTemplate(TEMPLATE_FROM_USAGE_FUNCTION_BODY)
             val properties = Properties()
             properties.setProperty(FileTemplate.ATTRIBUTE_RETURN_TYPE, if (skipReturnType) "Unit" else func.getTypeReference()!!.getText())
@@ -641,8 +649,7 @@ class CallableBuilder(val config: CallableBuilderConfiguration) {
                 throw IncorrectOperationException("Failed to parse file template", e)
             }
 
-            val newBodyExpression = JetPsiFactory(func).createFunctionBody(bodyText)
-            func.getBodyExpression()!!.replace(newBodyExpression)
+            oldBody.replace(JetPsiFactory(func).createFunctionBody(bodyText))
         }
 
         private fun setupCallTypeArguments(callElement: JetCallElement, typeParameters: List<TypeParameterDescriptor>) {

idea/testData/quickfix/createFromUsage/createFunction/call/afterExtensionFunOnTrait.kt

@@ -0,0 +1,11 @@
+// "Create extension function 'foo'" "true"
+
+trait T
+
+fun test(t: T) {
+    val b: Boolean = t.foo("1", 2)
+}
+
+fun T.foo(s: String, i: Int): Boolean {
+    throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
+}

idea/testData/quickfix/createFromUsage/createFunction/call/afterFunOnTrait.kt

@@ -0,0 +1,9 @@
+// "Create function 'foo'" "true"
+
+trait T {
+    fun foo(s: String, i: Int): Boolean
+}
+
+fun test(t: T) {
+    val b: Boolean = t.foo("1", 2)
+}

idea/testData/quickfix/createFromUsage/createFunction/call/beforeExtensionFunOnTrait.kt

@@ -0,0 +1,7 @@
+// "Create extension function 'foo'" "true"
+
+trait T
+
+fun test(t: T) {
+    val b: Boolean = t.<caret>foo("1", 2)
+}

idea/testData/quickfix/createFromUsage/createFunction/call/beforeFunOnTrait.kt

@@ -0,0 +1,7 @@
+// "Create function 'foo'" "true"
+
+trait T
+
+fun test(t: T) {
+    val b: Boolean = t.<caret>foo("1", 2)
+}

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

@@ -1534,6 +1534,12 @@ public class QuickFixTestGenerated extends AbstractQuickFixTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("beforeExtensionFunOnTrait.kt")
+                public void testExtensionFunOnTrait() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("idea/testData/quickfix/createFromUsage/createFunction/call/beforeExtensionFunOnTrait.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("beforeFunExtraArgs.kt")
                 public void testFunExtraArgs() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("idea/testData/quickfix/createFromUsage/createFunction/call/beforeFunExtraArgs.kt");
@@ -1570,6 +1576,12 @@ public class QuickFixTestGenerated extends AbstractQuickFixTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("beforeFunOnTrait.kt")
+                public void testFunOnTrait() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("idea/testData/quickfix/createFromUsage/createFunction/call/beforeFunOnTrait.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("beforeFunOnUserObject.kt")
                 public void testFunOnUserObject() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("idea/testData/quickfix/createFromUsage/createFunction/call/beforeFunOnUserObject.kt");