FIR: Support callable references to declarations with implicit types

^KT-32725 In Progress

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/ResolverParts.kt

@@ -176,16 +176,22 @@ internal object CheckCallableReferenceExpectedType : CheckerStage() {
     override suspend fun check(candidate: Candidate, sink: CheckerSink, callInfo: CallInfo) {
         val outerCsBuilder = callInfo.outerCSBuilder ?: return
         val expectedType = callInfo.expectedType ?: return
+        val candidateSymbol = candidate.symbol as? FirCallableSymbol<*> ?: return
 
         val resultingReceiverType = when (callInfo.lhs) {
             is DoubleColonLHS.Type -> callInfo.lhs.type.takeIf { callInfo.explicitReceiver !is FirResolvedQualifier }
             else -> null
         }
 
-        val fir = candidate.symbol.fir
+        val fir = with(candidate.bodyResolveComponents) {
+            candidateSymbol.phasedFir
+        }
+
+        val returnTypeRef = candidate.bodyResolveComponents.returnTypeCalculator.tryCalculateReturnType(fir)
+
         val resultingType: ConeKotlinType = when (fir) {
-            is FirSimpleFunction -> createKFunctionType(fir, resultingReceiverType)
+            is FirSimpleFunction -> createKFunctionType(fir, resultingReceiverType, returnTypeRef)
-            is FirProperty -> createKPropertyType(fir, resultingReceiverType)
+            is FirProperty -> createKPropertyType(fir, resultingReceiverType, returnTypeRef)
             else -> ConeKotlinErrorType("Unknown callable kind: ${fir::class}")
         }.let(candidate.substitutor::substituteOrSelf)
 
@@ -224,9 +230,10 @@ internal object CheckCallableReferenceExpectedType : CheckerStage() {
 
 private fun createKPropertyType(
     property: FirProperty,
-    receiverType: ConeKotlinType?
+    receiverType: ConeKotlinType?,
+    returnTypeRef: FirResolvedTypeRef
 ): ConeKotlinType {
-    val propertyType = property.returnTypeRef.coneTypeSafe<ConeKotlinType>() ?: ConeKotlinErrorType("No type for of $property")
+    val propertyType = returnTypeRef.coneTypeSafe<ConeKotlinType>() ?: ConeKotlinErrorType("No type for of $property")
     return createKPropertyType(
         receiverType, propertyType
     )
@@ -234,7 +241,8 @@ private fun createKPropertyType(
 
 private fun createKFunctionType(
     function: FirSimpleFunction,
-    receiverType: ConeKotlinType?
+    receiverType: ConeKotlinType?,
+    returnTypeRef: FirResolvedTypeRef
 ): ConeKotlinType {
     val parameterTypes = function.valueParameters.map {
         it.returnTypeRef.coneTypeSafe<ConeKotlinType>() ?: ConeKotlinErrorType("No type for parameter $it")
@@ -242,7 +250,7 @@ private fun createKFunctionType(
 
     return createFunctionalType(
         parameterTypes, receiverType = receiverType,
-        rawReturnType = function.returnTypeRef.coneTypeSafe() ?: ConeKotlinErrorType("No type for return type of $function"),
+        rawReturnType = returnTypeRef.coneTypeSafe() ?: ConeKotlinErrorType("No type for return type of $function"),
         isKFunctionType = true
     )
 }

compiler/fir/resolve/testData/diagnostics/callableReferences/implicitTypes.kt

@@ -0,0 +1,7 @@
+fun <T, R> use(x: (T) -> R): (T) -> R = x
+
+fun foo() = use(::bar)
+fun bar(x: String) = 1
+
+fun loop1() = use(::loop2)
+fun loop2() = loop1()

compiler/fir/resolve/testData/diagnostics/callableReferences/implicitTypes.txt

@@ -0,0 +1,16 @@
+FILE: implicitTypes.kt
+    public final fun <T, R> use(x: R|kotlin/Function1<T, R>|): R|kotlin/Function1<T, R>| {
+        ^use R|<local>/x|
+    }
+    public final fun foo(): R|kotlin/Function1<kotlin/String, kotlin/Int>| {
+        ^foo R|/use|<R|kotlin/String|, R|kotlin/Int|>(::R|/bar|)
+    }
+    public final fun bar(x: R|kotlin/String|): R|kotlin/Int| {
+        ^bar Int(1)
+    }
+    public final fun loop1(): <ERROR TYPE REF: Inapplicable(INAPPLICABLE): [/use]> {
+        ^loop1 <Inapplicable(INAPPLICABLE): [/use]>#(::loop2#)
+    }
+    public final fun loop2(): <ERROR TYPE REF: cycle> {
+        ^loop2 R?C|/loop1|()
+    }

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java

@@ -55,6 +55,11 @@ public class FirDiagnosticsTestGenerated extends AbstractFirDiagnosticsTest {
             runTest("compiler/fir/resolve/testData/diagnostics/callableReferences/extensionReceiverInference.kt");
         }
 
+        @TestMetadata("implicitTypes.kt")
+        public void testImplicitTypes() throws Exception {
+            runTest("compiler/fir/resolve/testData/diagnostics/callableReferences/implicitTypes.kt");
+        }
+
         @TestMetadata("inferenceFromCallableReferenceType.kt")
         public void testInferenceFromCallableReferenceType() throws Exception {
             runTest("compiler/fir/resolve/testData/diagnostics/callableReferences/inferenceFromCallableReferenceType.kt");