Implement callable references to suspend functions

In FE they have type KSuspendFunctionN
In BE they are treated like normal callable references with additional
parameter in invoke function.

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/CallCompleter.kt

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.resolve.calls
 import org.jetbrains.kotlin.builtins.getReturnTypeFromFunctionType
 import org.jetbrains.kotlin.builtins.getValueParameterTypesFromFunctionType
 import org.jetbrains.kotlin.builtins.isFunctionType
+import org.jetbrains.kotlin.builtins.isSuspendFunctionType
 import org.jetbrains.kotlin.contracts.EffectSystem
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
@@ -160,7 +161,8 @@ class CallCompleter(
         val expectedReturnType =
             if (call.isCallableReference()) {
                 // TODO: compute generic type argument for R in the kotlin.Function<R> supertype (KT-12963)
-                if (!TypeUtils.noExpectedType(expectedType) && expectedType.isFunctionType) expectedType.getReturnTypeFromFunctionType()
+                if (!TypeUtils.noExpectedType(expectedType) && (expectedType.isFunctionType || expectedType.isSuspendFunctionType))
+                    expectedType.getReturnTypeFromFunctionType()
                 else TypeUtils.NO_EXPECTED_TYPE
             } else expectedType
 
@@ -211,7 +213,7 @@ class CallCompleter(
             }
         }
 
-        if (call.isCallableReference() && !TypeUtils.noExpectedType(expectedType) && expectedType.isFunctionType) {
+        if (call.isCallableReference() && !TypeUtils.noExpectedType(expectedType) && (expectedType.isFunctionType || expectedType.isSuspendFunctionType)) {
             updateSystemIfNeeded { builder ->
                 candidateDescriptor.valueParameters.zip(expectedType.getValueParameterTypesFromFunctionType())
                     .forEach { (parameter, argument) ->

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/coroutineCallChecker.kt

@@ -15,6 +15,7 @@ import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
 import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.psi.KtCallableReferenceExpression
 import org.jetbrains.kotlin.psi.KtExpression
 import org.jetbrains.kotlin.psi.KtThisExpression
 import org.jetbrains.kotlin.resolve.BindingContext
@@ -59,6 +60,8 @@ object CoroutineSuspendCallChecker : CallChecker {
                     it.ownerDescriptor.safeAs<FunctionDescriptor>()?.isSuspend == true
         }?.cast<LexicalScope>()?.ownerDescriptor?.cast<FunctionDescriptor>()
 
+        val isCallableReference = resolvedCall.call.callElement.parent is KtCallableReferenceExpression
+
         when {
             enclosingSuspendFunction != null -> {
                 val callElement = resolvedCall.call.callElement as KtExpression
@@ -77,6 +80,9 @@ object CoroutineSuspendCallChecker : CallChecker {
 
                 checkRestrictsSuspension(enclosingSuspendFunction, resolvedCall, reportOn, context)
             }
+            isCallableReference -> {
+                // do nothing: we can get callable reference to suspend function outside suspend context
+            }
             else -> {
                 when (descriptor) {
                     is FunctionDescriptor -> context.trace.report(

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/DoubleColonExpressionResolver.kt

@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.types.expressions
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.builtins.ReflectionTypes
+import org.jetbrains.kotlin.builtins.isSuspendFunctionType
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.*
@@ -45,6 +46,7 @@ import org.jetbrains.kotlin.resolve.calls.util.CallMaker
 import org.jetbrains.kotlin.resolve.calls.util.FakeCallableDescriptorForObject
 import org.jetbrains.kotlin.resolve.calls.util.createValueParametersForInvokeInFunctionType
 import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
+import org.jetbrains.kotlin.resolve.descriptorUtil.isExtensionProperty
 import org.jetbrains.kotlin.resolve.scopes.receivers.ClassQualifier
 import org.jetbrains.kotlin.resolve.scopes.receivers.ExpressionReceiver
 import org.jetbrains.kotlin.resolve.scopes.receivers.Receiver
@@ -585,7 +587,7 @@ class DoubleColonExpressionResolver(
             Annotations.EMPTY,
             CallableMemberDescriptor.Kind.DECLARATION,
             expression.toSourceElement(),
-            /* isCoroutine = */ false
+            /* isCoroutine = */ ReflectionTypes.isKSuspendFunction(type)
         )
 
         functionDescriptor.initialize(
@@ -636,8 +638,8 @@ class DoubleColonExpressionResolver(
     ) {
         val descriptor =
             if (resolutionResults?.isSingleResult == true) resolutionResults.resultingDescriptor as? FunctionDescriptor else null
-        if (descriptor?.isSuspend == true) {
-            context.trace.report(UNSUPPORTED.on(expression.callableReference, "Callable references to suspend functions"))
+        if (descriptor?.isSuspend == true && descriptor is PropertyDescriptor) {
+            context.trace.report(UNSUPPORTED.on(expression.callableReference, "Callable references to suspend property"))
         }
 
         val expressionResult = lhsResult as? DoubleColonLHS.Expression ?: return
@@ -783,7 +785,11 @@ class DoubleColonExpressionResolver(
                     val returnType = descriptor.returnType ?: return null
                     val parametersTypes = descriptor.valueParameters.map { it.type }
                     val parametersNames = descriptor.valueParameters.map { it.name }
-                    return reflectionTypes.getKFunctionType(
+                    return if (descriptor.isSuspend) reflectionTypes.getKSuspendFunctionType(
+                        Annotations.EMPTY, receiverType,
+                        parametersTypes, parametersNames, returnType, descriptor.builtIns
+                    )
+                    else reflectionTypes.getKFunctionType(
                         Annotations.EMPTY, receiverType,
                         parametersTypes, parametersNames, returnType, descriptor.builtIns
                     )