Improve toString() for lambdas and function expressions

#KT-9952 Fixed

core/reflection.jvm/src/kotlin/reflect/jvm/internal/ReflectionFactoryImpl.java

@@ -18,6 +18,8 @@ package kotlin.reflect.jvm.internal;
 
 import kotlin.jvm.internal.*;
 import kotlin.reflect.*;
+import kotlin.reflect.jvm.ReflectLambdaKt;
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor;
 
 /**
  * @suppress
@@ -49,6 +51,18 @@ public class ReflectionFactoryImpl extends ReflectionFactory {
         return KClassCacheKt.getOrCreateKotlinClass(javaClass);
     }
 
+    @Override
+    public String renderLambdaToString(Lambda lambda) {
+        KFunction kFunction = ReflectLambdaKt.reflect(lambda);
+        if (kFunction != null) {
+            KFunctionImpl impl = UtilKt.asKFunctionImpl(kFunction);
+            if (impl != null) {
+                return ReflectionObjectRenderer.INSTANCE.renderLambda(impl.getDescriptor());
+            }
+        }
+        return super.renderLambdaToString(lambda);
+    }
+
     // Functions
 
     @Override

core/reflection.jvm/src/kotlin/reflect/jvm/internal/ReflectionObjectRenderer.kt

@@ -34,7 +34,7 @@ internal object ReflectionObjectRenderer {
         }
     }
 
-    private fun StringBuilder.appendReceiversAndName(callable: CallableDescriptor) {
+    private fun StringBuilder.appendReceivers(callable: CallableDescriptor) {
         val dispatchReceiver = callable.dispatchReceiverParameter
         val extensionReceiver = callable.extensionReceiverParameter
 
@@ -44,8 +44,6 @@ internal object ReflectionObjectRenderer {
         if (addParentheses) append("(")
         appendReceiverType(extensionReceiver)
         if (addParentheses) append(")")
-
-        append(renderer.renderName(callable.name))
     }
 
     fun renderCallable(descriptor: CallableDescriptor): String {
@@ -60,7 +58,8 @@ internal object ReflectionObjectRenderer {
     fun renderProperty(descriptor: PropertyDescriptor): String {
         return buildString {
             append(if (descriptor.isVar) "var " else "val ")
-            appendReceiversAndName(descriptor)
+            appendReceivers(descriptor)
+            append(renderer.renderName(descriptor.name))
 
             append(": ")
             append(renderType(descriptor.type))
@@ -70,7 +69,8 @@ internal object ReflectionObjectRenderer {
     fun renderFunction(descriptor: FunctionDescriptor): String {
         return buildString {
             append("fun ")
-            appendReceiversAndName(descriptor)
+            appendReceivers(descriptor)
+            append(renderer.renderName(descriptor.name))
 
             descriptor.valueParameters.joinTo(this, separator = ", ", prefix = "(", postfix = ")") {
                 renderType(it.type) // TODO: vararg
@@ -81,6 +81,19 @@ internal object ReflectionObjectRenderer {
         }
     }
 
+    fun renderLambda(invoke: FunctionDescriptor): String {
+        return buildString {
+            appendReceivers(invoke)
+
+            invoke.valueParameters.joinTo(this, separator = ", ", prefix = "(", postfix = ")") {
+                renderType(it.type)
+            }
+
+            append(" -> ")
+            append(renderType(invoke.returnType!!))
+        }
+    }
+
     fun renderParameter(parameter: KParameterImpl): String {
         return buildString {
             when (parameter.kind) {