KT-12669 Completion should show variant with () when there is default lambda

#KT-12669

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/InsertHandlerProvider.kt

@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.idea.core.ExpectedInfo
 import org.jetbrains.kotlin.idea.core.fuzzyType
 import org.jetbrains.kotlin.idea.util.CallType
 import org.jetbrains.kotlin.idea.util.fuzzyReturnType
+import org.jetbrains.kotlin.resolve.descriptorUtil.hasDefaultValue
 import org.jetbrains.kotlin.resolve.getValueParametersCountFromFunctionType
 import org.jetbrains.kotlin.types.KotlinType
 import java.util.*
@@ -48,9 +49,10 @@ class InsertHandlerProvider(
 
                             1 -> {
                                 if (callType != CallType.SUPER_MEMBERS) { // for super call we don't suggest to generate "super.foo { ... }" (seems to be non-typical use)
-                                    val parameterType = parameters.single().type
+                                    val parameter = parameters.single()
+                                    val parameterType = parameter.type
                                     if (parameterType.isFunctionType) {
-                                        if (getValueParametersCountFromFunctionType(parameterType) <= 1) {
+                                        if (getValueParametersCountFromFunctionType(parameterType) <= 1 && !parameter.hasDefaultValue()) {
                                             // otherwise additional item with lambda template is to be added
                                             return KotlinFunctionInsertHandler.Normal(
                                                     callType, needTypeArguments, inputValueArguments = false,

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/LookupElementFactory.kt

@@ -140,9 +140,9 @@ class LookupElementFactory(
             val isSingleParameter = descriptor.valueParameters.size == 1
 
             val parameterType = lastParameter.type
-            val functionParameterCount = getValueParametersCountFromFunctionType(parameterType)
+            val insertHandler = insertHandlerProvider.insertHandler(descriptor) as KotlinFunctionInsertHandler.Normal
-            // we don't need special item inserting lambda for single functional parameter that does not need multiple arguments because the default item will be special in this case
+            if (insertHandler.lambdaInfo == null) {
-            if (!isSingleParameter || functionParameterCount > 1) {
+                val functionParameterCount = getValueParametersCountFromFunctionType(parameterType)
                 add(createFunctionCallElementWithLambda(descriptor, parameterType, functionParameterCount > 1, useReceiverTypes))
             }
 
@@ -210,7 +210,7 @@ class LookupElementFactory(
     }
 
     private fun createFunctionCallElementWithArguments(descriptor: FunctionDescriptor, argumentText: String, useReceiverTypes: Boolean): LookupElement {
-        var lookupElement = createLookupElement(descriptor, useReceiverTypes)
+        val lookupElement = createLookupElement(descriptor, useReceiverTypes)
 
         val needTypeArguments = (insertHandlerProvider.insertHandler(descriptor) as KotlinFunctionInsertHandler.Normal).inputTypeArguments
         return FunctionCallWithArgumentsLookupElement(lookupElement, descriptor, argumentText, needTypeArguments)

idea/idea-completion/testData/basic/common/highOrderFunctions/OptionalParameters.kt

@@ -1,6 +1,7 @@
 fun xfoo1(option1: String = "", option2: Int = 1, p: () -> Unit){}
 fun xfoo2(option1: String = "", option2: Int = 1, p: (Int) -> Boolean){}
 fun xfoo3(option1: String = "", option2: Int = 1, p: (String, Char) -> Unit){}
+fun xfoo4(p: () -> Unit = {}){}
 
 fun xfooBad1(option: String = "", notOption: Int, p: (String, Char) -> Unit){}
 fun xfooBad2(option1: String = "", option2: Int = 1, p: (String, Char) -> Unit, option3: Int = 0){}
@@ -18,6 +19,10 @@ fun test(param: () -> Unit) {
 // EXIST: { itemText: "xfoo3", tailText: "(option1: String = ..., option2: Int = ..., p: (String, Char) -> Unit) (<root>)", typeText:"Unit" }
 // EXIST: { itemText: "xfoo3", tailText: " { String, Char -> ... } (..., p: (String, Char) -> Unit) (<root>)", typeText:"Unit" }
 
+// EXIST: { itemText: "xfoo4", tailText: "(p: () -> Unit = ...) (<root>)", typeText:"Unit" }
+// EXIST: { itemText: "xfoo4", tailText: " {...} (p: () -> Unit = ...) (<root>)", typeText:"Unit" }
+// EXIST: { itemText: "xfoo4", tailText: "(param) (<root>)", typeText:"Unit" }
+
 // EXIST: { itemText: "xfooBad1", tailText: "(option: String = ..., notOption: Int, p: (String, Char) -> Unit) (<root>)", typeText:"Unit" }
 
 // EXIST: { itemText: "xfooBad2", tailText: "(option1: String = ..., option2: Int = ..., p: (String, Char) -> Unit, option3: Int = ...) (<root>)", typeText:"Unit" }

idea/idea-completion/testData/handlers/basic/highOrderFunctions/OptionalParameters3.kt

@@ -0,0 +1,9 @@
+fun xfoo(p: () -> Unit = {}){}
+
+fun test() {
+    xfo<caret>
+}
+
+// ELEMENT: xfoo
+// TAIL_TEXT: " {...} (p: () -> Unit = ...) (<root>)"
+

idea/idea-completion/testData/handlers/basic/highOrderFunctions/OptionalParameters3.kt.after

@@ -0,0 +1,9 @@
+fun xfoo(p: () -> Unit = {}){}
+
+fun test() {
+    xfoo { <caret> }
+}
+
+// ELEMENT: xfoo
+// TAIL_TEXT: " {...} (p: () -> Unit = ...) (<root>)"
+

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/handlers/BasicCompletionHandlerTestGenerated.java

@@ -385,6 +385,12 @@ public class BasicCompletionHandlerTestGenerated extends AbstractBasicCompletion
             doTest(fileName);
         }
 
+        @TestMetadata("OptionalParameters3.kt")
+        public void testOptionalParameters3() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/handlers/basic/highOrderFunctions/OptionalParameters3.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("ParameterTypeIsDerivedFromFunction.kt")
         public void testParameterTypeIsDerivedFromFunction() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/handlers/basic/highOrderFunctions/ParameterTypeIsDerivedFromFunction.kt");