More accurate safe call handling in GenericCandidateResolver / CallExpressionResolver

(real receiver nullability is taken into account)

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/CallExpressionResolver.java

@@ -441,8 +441,9 @@ public class CallExpressionResolver {
             }
 
             DataFlowInfo initialDataFlowInfoForArguments = contextForSelector.dataFlowInfo;
+            DataFlowValue receiverDataFlowValue = null;
             if (receiver instanceof ReceiverValue) {
-                DataFlowValue receiverDataFlowValue = DataFlowValueFactory.createDataFlowValue((ReceiverValue) receiver, context);
+                receiverDataFlowValue = DataFlowValueFactory.createDataFlowValue((ReceiverValue) receiver, context);
                 // Additional "receiver != null" information
                 // Should be applied if we consider a safe call
                 if (element.getSafe()) {
@@ -467,7 +468,8 @@ public class CallExpressionResolver {
             checkNestedClassAccess(element.getQualified(), contextForSelector);
 
             boolean safeCall = element.getSafe();
-            if (safeCall && selectorReturnType != null && TypeUtils.isNullableType(receiverType)) {
+            if (safeCall && selectorReturnType != null && receiverDataFlowValue != null &&
+                contextForSelector.dataFlowInfo.getPredictableNullability(receiverDataFlowValue).canBeNull()) {
                 selectorReturnType = TypeUtils.makeNullable(selectorReturnType);
                 selectorReturnTypeInfo = selectorReturnTypeInfo.replaceType(selectorReturnType);
             }

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

@@ -36,7 +36,7 @@ import org.jetbrains.kotlin.resolve.calls.inference.*
 import org.jetbrains.kotlin.resolve.calls.inference.constraintPosition.ConstraintPosition
 import org.jetbrains.kotlin.resolve.calls.inference.constraintPosition.ConstraintPositionKind.RECEIVER_POSITION
 import org.jetbrains.kotlin.resolve.calls.inference.constraintPosition.ConstraintPositionKind.VALUE_PARAMETER_POSITION
-import org.jetbrains.kotlin.resolve.calls.resolvedCallUtil.getExplicitReceiverValue
+import org.jetbrains.kotlin.resolve.calls.resolvedCallUtil.makeNullableTypeIfSafeReceiver
 import org.jetbrains.kotlin.resolve.calls.results.ResolutionStatus
 import org.jetbrains.kotlin.resolve.calls.results.ResolutionStatus.INCOMPLETE_TYPE_INFERENCE
 import org.jetbrains.kotlin.resolve.calls.results.ResolutionStatus.OTHER_ERROR
@@ -174,13 +174,8 @@ class GenericCandidateResolver(private val argumentTypeResolver: ArgumentTypeRes
 
         val freshVariables = returnType.getNestedTypeParameters().mapNotNull { conversion[it] }
         builder.registerTypeVariables(nestedCall.call.toHandle(), freshVariables, external = true)
-        // Looks not too nice, but safe call result must be nullable if receiver is nullable
-        val argumentExpressionType = candidateWithFreshVariables.returnType?.let {
-            if (nestedCall.isSafeCall && nestedCall.getExplicitReceiverValue()?.type?.let {TypeUtils.isNullableType(it) } ?: true ) {
-                TypeUtils.makeNullable(it)
-            }
-            else it
-        }
+        // Safe call result must be nullable if receiver is nullable
+        val argumentExpressionType = nestedCall.makeNullableTypeIfSafeReceiver(candidateWithFreshVariables.returnType, context)
 
         builder.addSubtypeConstraint(
                 argumentExpressionType,

compiler/testData/diagnostics/tests/generics/kt9985.kt

@@ -26,6 +26,10 @@ fun foo(l: A<String>?) {
     // No errors should be here
     foo(l?.bar()) checkType { _<String?>() }
     foo(l?.gav()) checkType { _<String?>() }
+    if (l != null) {
+        foo(l<!UNNECESSARY_SAFE_CALL!>?.<!>bar()) checkType { _<String>() }
+        foo(l<!UNNECESSARY_SAFE_CALL!>?.<!>gav()) checkType { _<String>() }
+    }
 }
 
 fun fooNotNull(l: A<String>) {