KT-39532 Support intention to convert reference to lambda and vice versa for adapted references (#3495)

* Convert lambda to reference: support a function which has default parameters/unit return type/suspendability

#KT-39532 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/ConvertLambdaToReferenceIntention.kt

@@ -32,6 +32,7 @@ import org.jetbrains.kotlin.resolve.calls.callUtil.getParameterForArgument
 import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
 import org.jetbrains.kotlin.resolve.calls.components.hasDefaultValue
 import org.jetbrains.kotlin.resolve.calls.components.isVararg
+import org.jetbrains.kotlin.resolve.calls.model.DefaultValueArgument
 import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
 import org.jetbrains.kotlin.resolve.calls.model.VarargValueArgument
 import org.jetbrains.kotlin.resolve.descriptorUtil.isCompanionObject
@@ -63,6 +64,7 @@ open class ConvertLambdaToReferenceIntention(textGetter: () -> String) : SelfTar
         explicitReceiver: KtExpression? = null,
         lambdaExpression: KtLambdaExpression
     ): Boolean {
+        val languageVersionSettings = callableExpression.languageVersionSettings
         val context = callableExpression.analyze()
         val calleeReferenceExpression = when (callableExpression) {
             is KtCallExpression -> callableExpression.calleeExpression as? KtNameReferenceExpression ?: return false
@@ -80,7 +82,10 @@ open class ConvertLambdaToReferenceIntention(textGetter: () -> String) : SelfTar
 
         val lambdaParameterIsSuspend = lambdaParameterType?.isSuspendFunctionType == true
         val calleeFunctionIsSuspend = (calleeDescriptor as? FunctionDescriptor)?.isSuspend == true
-        if (lambdaParameterIsSuspend && !calleeFunctionIsSuspend || !lambdaParameterIsSuspend && calleeFunctionIsSuspend) return false
+        if (!lambdaParameterIsSuspend && calleeFunctionIsSuspend) return false
+        if (lambdaParameterIsSuspend && !calleeFunctionIsSuspend &&
+            !languageVersionSettings.supportsFeature(LanguageFeature.SuspendConversion)
+        ) return false
 
         // No references with type parameters
         if (calleeDescriptor.typeParameters.isNotEmpty()) return false
@@ -94,17 +99,25 @@ open class ConvertLambdaToReferenceIntention(textGetter: () -> String) : SelfTar
         }
 
         if (!descriptorHasReceiver && explicitReceiver != null && calleeDescriptor !is ClassConstructorDescriptor) return false
-        val noBoundReferences = !callableExpression.languageVersionSettings.supportsFeature(LanguageFeature.BoundCallableReferences)
+        val noBoundReferences = !languageVersionSettings.supportsFeature(LanguageFeature.BoundCallableReferences)
         if (noBoundReferences && descriptorHasReceiver && explicitReceiver == null) return false
 
         val callableArgumentsCount = (callableExpression as? KtCallExpression)?.valueArguments?.size ?: 0
-        if (calleeDescriptor.valueParameters.size != callableArgumentsCount) return false
+        val enableFunctionReferenceWithDefaultValueAsOtherType =
-        val lambdaMustReturnUnit =
+            languageVersionSettings.supportsFeature(LanguageFeature.FunctionReferenceWithDefaultValueAsOtherType)
-            if (lambdaParameterType?.isFunctionType == true) lambdaParameterType.getReturnTypeFromFunctionType().isUnit() else false
+        if (enableFunctionReferenceWithDefaultValueAsOtherType) {
-        if (lambdaMustReturnUnit) {
+            if (calleeDescriptor.valueParameters.size != callableArgumentsCount &&
-            calleeDescriptor.returnType.let {
+                (lambdaExpression.parentValueArgument() == null || calleeDescriptor.valueParameters.none { it.declaresDefaultValue() })
-                // If Unit required, no references to non-Unit callables
+            ) return false
-                if (it == null || !it.isUnit()) return false
+        } else {
+            if (calleeDescriptor.valueParameters.size != callableArgumentsCount) return false
+            val lambdaMustReturnUnit =
+                if (lambdaParameterType?.isFunctionType == true) lambdaParameterType.getReturnTypeFromFunctionType().isUnit() else false
+            if (lambdaMustReturnUnit) {
+                calleeDescriptor.returnType.let {
+                    // If Unit required, no references to non-Unit callables
+                    if (it == null || !it.isUnit()) return false
+                }
             }
         }
 
@@ -137,6 +150,7 @@ open class ConvertLambdaToReferenceIntention(textGetter: () -> String) : SelfTar
             if (lambdaValueParameterDescriptors.size < explicitReceiverShift + callableExpression.valueArguments.size) return false
             val resolvedCall = callableExpression.getResolvedCall(context) ?: return false
             resolvedCall.valueArguments.entries.forEach { (valueParameter, resolvedArgument) ->
+                if (resolvedArgument is DefaultValueArgument && enableFunctionReferenceWithDefaultValueAsOtherType) return@forEach
                 val argument = resolvedArgument.arguments.singleOrNull() ?: return false
                 if (resolvedArgument is VarargValueArgument && argument.getSpreadElement() == null) return false
                 val argumentExpression = argument.getArgumentExpression() as? KtNameReferenceExpression ?: return false

idea/testData/intentions/convertLambdaToReference/defaultArgument.kt

@@ -1,4 +1,5 @@
 // IS_APPLICABLE: false
+// COMPILER_ARGUMENTS: -XXLanguage:-FunctionReferenceWithDefaultValueAsOtherType
 
 fun foo(z: Int, y: Int = 0) = y + z
 

idea/testData/intentions/convertLambdaToReference/defaultArgument2.kt

@@ -0,0 +1,5 @@
+// IS_APPLICABLE: false
+
+fun foo(z: Int, y: Int = 0) = y + z
+
+val x = { arg: Int <caret>-> foo(arg) }

idea/testData/intentions/convertLambdaToReference/defaultArgument3.kt

@@ -0,0 +1,7 @@
+fun foo(f: () -> Unit) {}
+
+fun bar(a: Int = 42) {}
+
+fun test() {
+    foo <caret>{ bar() }
+}

idea/testData/intentions/convertLambdaToReference/defaultArgument3.kt.after

@@ -0,0 +1,7 @@
+fun foo(f: () -> Unit) {}
+
+fun bar(a: Int = 42) {}
+
+fun test() {
+    foo(::bar)
+}

idea/testData/intentions/convertLambdaToReference/defaultArgument4.kt

@@ -0,0 +1,7 @@
+fun foo(f: (x: Int) -> Unit) {}
+
+fun bar(x: Int, y: Int = 42) {}
+
+fun test() {
+    foo <caret>{ bar(it) }
+}

idea/testData/intentions/convertLambdaToReference/defaultArgument4.kt.after

@@ -0,0 +1,7 @@
+fun foo(f: (x: Int) -> Unit) {}
+
+fun bar(x: Int, y: Int = 42) {}
+
+fun test() {
+    foo(::bar)
+}

idea/testData/intentions/convertLambdaToReference/defaultArgument5.kt

@@ -0,0 +1,7 @@
+fun Int.foo(x: Int, y: Int = 42) = x + y
+
+fun bar(f: (Int, Int) -> Int) {}
+
+fun test() {
+    bar <caret>{ i, x -> i.foo(x) }
+}

idea/testData/intentions/convertLambdaToReference/defaultArgument5.kt.after

@@ -0,0 +1,7 @@
+fun Int.foo(x: Int, y: Int = 42) = x + y
+
+fun bar(f: (Int, Int) -> Int) {}
+
+fun test() {
+    bar(Int::foo)
+}

idea/testData/intentions/convertLambdaToReference/suspendFunctionParameter.kt

@@ -1,4 +1,5 @@
 // IS_APPLICABLE: false
+// COMPILER_ARGUMENTS: -XXLanguage:-SuspendConversion
 
 fun coroutine(block: suspend () -> Unit) {}
 

idea/testData/intentions/convertLambdaToReference/suspendFunctionParameter3.kt

@@ -0,0 +1,8 @@
+// COMPILER_ARGUMENTS: -XXLanguage:+SuspendConversion
+fun foo(a: suspend () -> Unit) {}
+
+fun action() {}
+
+fun usage() {
+    foo { action() <caret> }
+}

idea/testData/intentions/convertLambdaToReference/suspendFunctionParameter3.kt.after

@@ -0,0 +1,8 @@
+// COMPILER_ARGUMENTS: -XXLanguage:+SuspendConversion
+fun foo(a: suspend () -> Unit) {}
+
+fun action() {}
+
+fun usage() {
+    foo(::action)
+}

idea/testData/intentions/convertLambdaToReference/unit.kt

@@ -1,4 +1,5 @@
 // IS_APPLICABLE: false
+// COMPILER_ARGUMENTS: -XXLanguage:-FunctionReferenceWithDefaultValueAsOtherType
 
 fun Int.exec(f: (Int) -> Unit) = f(this)
 

idea/testData/intentions/convertLambdaToReference/unit2.kt

@@ -0,0 +1,7 @@
+fun Int.exec(f: (Int) -> Unit) = f(this)
+
+fun bar(x: Int) = x
+
+fun foo() {
+    2.exec {<caret> bar(it) }
+}

idea/testData/intentions/convertLambdaToReference/unit2.kt.after

@@ -0,0 +1,7 @@
+fun Int.exec(f: (Int) -> Unit) = f(this)
+
+fun bar(x: Int) = x
+
+fun foo() {
+    2.exec(::bar)
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -4990,6 +4990,26 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             runTest("idea/testData/intentions/convertLambdaToReference/defaultArgument.kt");
         }
 
+        @TestMetadata("defaultArgument2.kt")
+        public void testDefaultArgument2() throws Exception {
+            runTest("idea/testData/intentions/convertLambdaToReference/defaultArgument2.kt");
+        }
+
+        @TestMetadata("defaultArgument3.kt")
+        public void testDefaultArgument3() throws Exception {
+            runTest("idea/testData/intentions/convertLambdaToReference/defaultArgument3.kt");
+        }
+
+        @TestMetadata("defaultArgument4.kt")
+        public void testDefaultArgument4() throws Exception {
+            runTest("idea/testData/intentions/convertLambdaToReference/defaultArgument4.kt");
+        }
+
+        @TestMetadata("defaultArgument5.kt")
+        public void testDefaultArgument5() throws Exception {
+            runTest("idea/testData/intentions/convertLambdaToReference/defaultArgument5.kt");
+        }
+
         @TestMetadata("defaultBeforeLambda.kt")
         public void testDefaultBeforeLambda() throws Exception {
             runTest("idea/testData/intentions/convertLambdaToReference/defaultBeforeLambda.kt");
@@ -5225,6 +5245,11 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             runTest("idea/testData/intentions/convertLambdaToReference/suspendFunctionParameter2.kt");
         }
 
+        @TestMetadata("suspendFunctionParameter3.kt")
+        public void testSuspendFunctionParameter3() throws Exception {
+            runTest("idea/testData/intentions/convertLambdaToReference/suspendFunctionParameter3.kt");
+        }
+
         @TestMetadata("syntheticProperty.kt")
         public void testSyntheticProperty() throws Exception {
             runTest("idea/testData/intentions/convertLambdaToReference/syntheticProperty.kt");
@@ -5295,6 +5320,11 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             runTest("idea/testData/intentions/convertLambdaToReference/unit.kt");
         }
 
+        @TestMetadata("unit2.kt")
+        public void testUnit2() throws Exception {
+            runTest("idea/testData/intentions/convertLambdaToReference/unit2.kt");
+        }
+
         @TestMetadata("unwrap.kt")
         public void testUnwrap() throws Exception {
             runTest("idea/testData/intentions/convertLambdaToReference/unwrap.kt");