Refactor FunctionReferenceGenerationStrategy

Draw a clear distinction between the referenced function's parameters
and the anonymous synthetic function's parameters (see the comment).
This will be useful in supporting advanced callable reference features
like KT-8834

compiler/backend-common/src/org/jetbrains/kotlin/backend/common/CodegenUtil.kt

@@ -156,10 +156,9 @@ object CodegenUtil {
     }
 
     @JvmStatic
-    fun constructFakeFunctionCall(project: Project, referencedFunction: FunctionDescriptor): KtCallExpression {
-        val fakeFunctionCall = StringBuilder("callableReferenceFakeCall(")
-        fakeFunctionCall.append(referencedFunction.valueParameters.joinToString(", ") { "p${it.index}" })
-        fakeFunctionCall.append(")")
-        return KtPsiFactory(project, markGenerated = false).createExpression(fakeFunctionCall.toString()) as KtCallExpression
+    fun constructFakeFunctionCall(project: Project, arity: Int): KtCallExpression {
+        val fakeFunctionCall =
+                (1..arity).joinToString(prefix = "callableReferenceFakeCall(", separator = ", ", postfix = ")") { "p$it" }
+        return KtPsiFactory(project, markGenerated = false).createExpression(fakeFunctionCall) as KtCallExpression
     }
 }

compiler/backend/src/org/jetbrains/kotlin/codegen/FunctionReferenceGenerationStrategy.java

@@ -24,10 +24,7 @@ import org.jetbrains.kotlin.codegen.state.GenerationState;
 import org.jetbrains.kotlin.descriptors.*;
 import org.jetbrains.kotlin.psi.*;
 import org.jetbrains.kotlin.resolve.BindingContext;
-import org.jetbrains.kotlin.resolve.calls.model.DelegatingResolvedCall;
-import org.jetbrains.kotlin.resolve.calls.model.ExpressionValueArgument;
-import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall;
-import org.jetbrains.kotlin.resolve.calls.model.ResolvedValueArgument;
+import org.jetbrains.kotlin.resolve.calls.model.*;
 import org.jetbrains.kotlin.resolve.calls.util.CallMaker;
 import org.jetbrains.kotlin.resolve.jvm.jvmSignature.JvmMethodSignature;
 import org.jetbrains.kotlin.resolve.scopes.receivers.ExpressionReceiver;
@@ -40,8 +37,24 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
-import static org.jetbrains.kotlin.resolve.DescriptorUtils.isObject;
-
+/*
+ * Notice the difference between two function descriptors in this class.
+ * - [referencedFunction] is the function declaration which is referenced by the "::" expression. This is a real function present in code.
+ * - [functionDescriptor] is a synthetically created function which has the same signature as the "invoke" of the generated callable
+ *   reference subclass. Its parameters include dispatch/extension receiver parameters of the referenced function, and those value
+ *   parameters of the referenced function which are required by the expected function type where the callable reference is passed to.
+ *   In simple cases, these value parameters are all of the referenced function's value parameters. But in cases when the referenced
+ *   function has parameters with default values, or a vararg parameter, functionDescriptor can take fewer parameters than
+ *   referencedFunction if the expected function type takes fewer parameters as well. For example:
+ *
+ * fun foo(a: A, b: B = ..., c: C = ..., vararg d: D) {}
+ *
+ * fun bar(f: (A, B) -> Unit) {}
+ *
+ * // referencedFunction: foo(A, B, C, vararg D)
+ * // functionDescriptor: invoke(A, B)
+ * bar(::foo)
+ */
 public class FunctionReferenceGenerationStrategy extends FunctionGenerationStrategy.CodegenBased {
     private final ResolvedCall<?> resolvedCall;
     private final FunctionDescriptor referencedFunction;
@@ -80,20 +93,21 @@ public class FunctionReferenceGenerationStrategy extends FunctionGenerationStrat
          every argument boils down to calling LOAD with the corresponding index
          */
 
-        KtCallExpression fakeExpression = CodegenUtil.constructFakeFunctionCall(state.getProject(), referencedFunction);
+        int receivers = CallableReferenceUtilKt.computeExpectedNumberOfReceivers(referencedFunction, receiverType != null);
+        KtCallExpression fakeExpression =
+                CodegenUtil.constructFakeFunctionCall(state.getProject(), functionDescriptor.getValueParameters().size() - receivers);
         List<? extends ValueArgument> fakeArguments = fakeExpression.getValueArguments();
 
         ReceiverValue dispatchReceiver = computeAndSaveReceiver(signature, codegen, referencedFunction.getDispatchReceiverParameter());
         ReceiverValue extensionReceiver = computeAndSaveReceiver(signature, codegen, referencedFunction.getExtensionReceiverParameter());
-        computeAndSaveArguments(fakeArguments, codegen);
+        computeAndSaveArguments(fakeArguments, codegen, receivers);
 
         ResolvedCall<CallableDescriptor> fakeResolvedCall = new DelegatingResolvedCall<CallableDescriptor>(resolvedCall) {
 
-            private final Map<ValueParameterDescriptor, ResolvedValueArgument> argumentMap;
+            private final Map<ValueParameterDescriptor, ResolvedValueArgument> argumentMap = new LinkedHashMap<>();
             {
-                argumentMap = new LinkedHashMap<>(fakeArguments.size());
                 int index = 0;
-                List<ValueParameterDescriptor> parameters = functionDescriptor.getValueParameters();
+                List<ValueParameterDescriptor> parameters = referencedFunction.getValueParameters();
                 for (ValueArgument argument : fakeArguments) {
                     argumentMap.put(parameters.get(index), new ExpressionValueArgument(argument));
                     index++;
@@ -146,20 +160,14 @@ public class FunctionReferenceGenerationStrategy extends FunctionGenerationStrat
         v.areturn(returnType);
     }
 
-    private void computeAndSaveArguments(@NotNull List<? extends ValueArgument> fakeArguments, @NotNull ExpressionCodegen codegen) {
-        int receivers = (referencedFunction.getDispatchReceiverParameter() != null ? 1 : 0) +
-                        (referencedFunction.getExtensionReceiverParameter() != null ? 1 : 0) -
-                        (receiverType != null ? 1 : 0);
-
-        if (receivers < 0 &&  referencedFunction instanceof ConstructorDescriptor && isObject(referencedFunction.getContainingDeclaration().getContainingDeclaration())) {
-            //reference to object nested class
-            //TODO: seems problem should be fixed on frontend side (note that object instance are captured by generated class)
-            receivers = 0;
-        }
-
-        List<ValueParameterDescriptor> parameters = CollectionsKt.drop(functionDescriptor.getValueParameters(), receivers);
-        for (int i = 0; i < parameters.size(); i++) {
-            ValueParameterDescriptor parameter = parameters.get(i);
+    private void computeAndSaveArguments(
+            @NotNull List<? extends ValueArgument> fakeArguments, @NotNull ExpressionCodegen codegen, int receivers
+    ) {
+        List<ValueParameterDescriptor> valueParameters = CollectionsKt.drop(functionDescriptor.getValueParameters(), receivers);
+        assert valueParameters.size() == fakeArguments.size()
+                : functionDescriptor + ": " + valueParameters.size() + " != " + fakeArguments.size();
+        for (int i = 0; i < valueParameters.size(); i++) {
+            ValueParameterDescriptor parameter = valueParameters.get(i);
             ValueArgument fakeArgument = fakeArguments.get(i);
 
             Type type = state.getTypeMapper().mapType(parameter);

compiler/backend/src/org/jetbrains/kotlin/codegen/JvmRuntimeTypes.kt

@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.codegen.coroutines.getOrCreateJvmSuspendFunctionView
 import org.jetbrains.kotlin.coroutines.isSuspendLambda
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
+import org.jetbrains.kotlin.descriptors.impl.AnonymousFunctionDescriptor
 import org.jetbrains.kotlin.descriptors.impl.LocalVariableDescriptor
 import org.jetbrains.kotlin.descriptors.impl.MutableClassDescriptor
 import org.jetbrains.kotlin.descriptors.impl.MutablePackageFragmentDescriptor
@@ -29,7 +30,6 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
 import org.jetbrains.kotlin.types.KotlinType
-import org.jetbrains.kotlin.types.expressions.ExpressionTypingUtils
 
 class JvmRuntimeTypes(module: ModuleDescriptor) {
     private val kotlinJvmInternalPackage = MutablePackageFragmentDescriptor(module, FqName("kotlin.jvm.internal"))
@@ -77,7 +77,7 @@ class JvmRuntimeTypes(module: ModuleDescriptor) {
                 descriptor.builtIns,
                 Annotations.EMPTY,
                 actualFunctionDescriptor.extensionReceiverParameter?.type,
-                ExpressionTypingUtils.getValueParametersTypes(actualFunctionDescriptor.valueParameters),
+                actualFunctionDescriptor.valueParameters.map { it.type },
                 null,
                 actualFunctionDescriptor.returnType!!
         )
@@ -94,14 +94,20 @@ class JvmRuntimeTypes(module: ModuleDescriptor) {
         return listOf(lambda.defaultType, functionType)
     }
 
-    fun getSupertypesForFunctionReference(descriptor: FunctionDescriptor, isBound: Boolean): Collection<KotlinType> {
+    fun getSupertypesForFunctionReference(
+            referencedFunction: FunctionDescriptor,
+            anonymousFunctionDescriptor: AnonymousFunctionDescriptor,
+            isBound: Boolean
+    ): Collection<KotlinType> {
+        val receivers = computeExpectedNumberOfReceivers(referencedFunction, isBound)
+
         val functionType = createFunctionType(
-                descriptor.builtIns,
+                referencedFunction.builtIns,
                 Annotations.EMPTY,
-                if (isBound) null else descriptor.extensionReceiverParameter?.type ?: descriptor.dispatchReceiverParameter?.type,
-                ExpressionTypingUtils.getValueParametersTypes(descriptor.valueParameters),
+                if (isBound) null else referencedFunction.extensionReceiverParameter?.type ?: referencedFunction.dispatchReceiverParameter?.type,
+                anonymousFunctionDescriptor.valueParameters.drop(receivers).map { it.type },
                 null,
-                descriptor.returnType!!
+                referencedFunction.returnType!!
         )
 
         return listOf(functionReference.defaultType, functionType)

compiler/backend/src/org/jetbrains/kotlin/codegen/binding/CodegenAnnotatingVisitor.java

@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.codegen.when.WhenByEnumsMapping;
 import org.jetbrains.kotlin.coroutines.CoroutineUtilKt;
 import org.jetbrains.kotlin.descriptors.*;
 import org.jetbrains.kotlin.descriptors.annotations.Annotations;
+import org.jetbrains.kotlin.descriptors.impl.AnonymousFunctionDescriptor;
 import org.jetbrains.kotlin.descriptors.impl.LocalVariableDescriptor;
 import org.jetbrains.kotlin.fileClasses.FileClasses;
 import org.jetbrains.kotlin.fileClasses.JvmFileClassesProvider;
@@ -341,7 +342,9 @@ class CodegenAnnotatingVisitor extends KtVisitorVoid {
             callableDescriptor = bindingContext.get(FUNCTION, expression);
             if (callableDescriptor == null) return;
 
-            supertypes = runtimeTypes.getSupertypesForFunctionReference((FunctionDescriptor) target, receiverType != null);
+            supertypes = runtimeTypes.getSupertypesForFunctionReference(
+                    (FunctionDescriptor) target, (AnonymousFunctionDescriptor) callableDescriptor, receiverType != null
+            );
         }
         else if (target instanceof PropertyDescriptor) {
             callableDescriptor = bindingContext.get(VARIABLE, expression);

compiler/backend/src/org/jetbrains/kotlin/codegen/callableReferenceUtil.kt

@@ -18,7 +18,10 @@ package org.jetbrains.kotlin.codegen
 
 import org.jetbrains.kotlin.codegen.binding.CalculatedClosure
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.ConstructorDescriptor
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.psi.KtCallableReferenceExpression
+import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.jvm.AsmTypes
 import org.jetbrains.kotlin.resolve.source.KotlinSourceElement
 import org.jetbrains.org.objectweb.asm.Type
@@ -75,4 +78,19 @@ fun InstructionAdapter.generateClosureFieldsInitializationFromParameters(closure
         else ->
             null
     }
-}
+}
+
+fun computeExpectedNumberOfReceivers(referencedFunction: FunctionDescriptor, isBound: Boolean): Int {
+    val receivers = (if (referencedFunction.dispatchReceiverParameter != null) 1 else 0) +
+                    (if (referencedFunction.extensionReceiverParameter != null) 1 else 0) -
+                    (if (isBound) 1 else 0)
+
+    if (receivers < 0 && referencedFunction is ConstructorDescriptor &&
+               DescriptorUtils.isObject(referencedFunction.containingDeclaration.containingDeclaration)) {
+        //reference to object nested class
+        //TODO: seems problem should be fixed on frontend side (note that object instance are captured by generated class)
+        return 0
+    }
+
+    return receivers
+}

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ExpressionTypingUtils.java

@@ -44,9 +44,6 @@ import org.jetbrains.kotlin.resolve.scopes.utils.ScopeUtilsKt;
 import org.jetbrains.kotlin.types.KotlinType;
 import org.jetbrains.kotlin.types.expressions.typeInfoFactory.TypeInfoFactoryKt;
 
-import java.util.ArrayList;
-import java.util.List;
-
 import static org.jetbrains.kotlin.diagnostics.Errors.TYPE_INFERENCE_ERRORS;
 import static org.jetbrains.kotlin.resolve.BindingContext.PROCESSED;
 
@@ -185,15 +182,6 @@ public class ExpressionTypingUtils {
                && ((KtUnaryExpression) expression).getOperationReference().getReferencedNameElementType() == KtTokens.EXCLEXCL;
     }
 
-    @NotNull
-    public static List<KotlinType> getValueParametersTypes(@NotNull List<ValueParameterDescriptor> valueParameters) {
-        List<KotlinType> parameterTypes = new ArrayList<>(valueParameters.size());
-        for (ValueParameterDescriptor parameter : valueParameters) {
-            parameterTypes.add(parameter.getType());
-        }
-        return parameterTypes;
-    }
-
     /**
      * The primary case for local extensions is the following:
      *

js/js.translator/src/org/jetbrains/kotlin/js/translate/reference/CallableReferenceTranslator.kt

@@ -82,7 +82,7 @@ object CallableReferenceTranslator {
             receiver: JsExpression?
     ): JsExpression {
         val realResolvedCall = expression.callableReference.getFunctionResolvedCallWithAssert(context.bindingContext())
-        val fakeExpression = CodegenUtil.constructFakeFunctionCall(expression.project, descriptor)
+        val fakeExpression = CodegenUtil.constructFakeFunctionCall(expression.project, descriptor.valueParameters.size)
 
         val fakeCall = CallMaker.makeCall(fakeExpression, null, null, fakeExpression, fakeExpression.valueArguments)
         val fakeResolvedCall = object : DelegatingResolvedCall<FunctionDescriptor>(realResolvedCall) {