Call completer: safe call with nullable receiver has nullable return type #KT-11007 Fixed

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

@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.resolve.calls.inference.constraintPosition.Constrain
 import org.jetbrains.kotlin.resolve.calls.inference.filterConstraintsOut
 import org.jetbrains.kotlin.resolve.calls.inference.toHandle
 import org.jetbrains.kotlin.resolve.calls.model.*
+import org.jetbrains.kotlin.resolve.calls.resolvedCallUtil.makeNullableTypeIfSafeReceiver
 import org.jetbrains.kotlin.resolve.calls.results.OverloadResolutionResultsImpl
 import org.jetbrains.kotlin.resolve.calls.results.ResolutionStatus
 import org.jetbrains.kotlin.resolve.calls.smartcasts.DataFlowInfo
@@ -274,7 +275,10 @@ class CallCompleter(
         val results = completeCallForArgument(deparenthesized, context)
         if (results != null && results.isSingleResult) {
             val resolvedCall = results.resultingCall
-            updatedType = if (resolvedCall.hasInferredReturnType()) resolvedCall.resultingDescriptor?.returnType else null
+            updatedType = if (resolvedCall.hasInferredReturnType()) {
+                resolvedCall.makeNullableTypeIfSafeReceiver(resolvedCall.resultingDescriptor?.returnType, context)
+            }
+            else null
         }
 
         // For the cases like 'foo(1)' the type of '1' depends on expected type (it can be Int, Byte, etc.),

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

@@ -16,16 +16,22 @@
 
 package org.jetbrains.kotlin.resolve.calls.resolvedCallUtil
 
+import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.psi.KtPsiUtil
 import org.jetbrains.kotlin.psi.KtThisExpression
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.calls.context.BasicCallResolutionContext
+import org.jetbrains.kotlin.resolve.calls.context.CallResolutionContext
 import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
+import org.jetbrains.kotlin.resolve.calls.smartcasts.DataFlowValueFactory
 import org.jetbrains.kotlin.resolve.calls.tasks.ExplicitReceiverKind
 import org.jetbrains.kotlin.resolve.descriptorUtil.getOwnerForEffectiveDispatchReceiverParameter
 import org.jetbrains.kotlin.resolve.scopes.receivers.ExpressionReceiver
 import org.jetbrains.kotlin.resolve.scopes.receivers.ImplicitReceiver
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValue
+import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.TypeUtils
 
 // it returns true if call has no dispatch receiver (e.g. resulting descriptor is top-level function or local variable)
 // or call receiver is effectively `this` instance (explicitly or implicitly) of resulting descriptor
@@ -72,4 +78,14 @@ fun ResolvedCall<*>.getImplicitReceiverValue(): ReceiverValue? {
     }
 }
 
+private fun ResolvedCall<*>.hasSafeNullableReceiver(context: CallResolutionContext<*>): Boolean {
+    if (!isSafeCall) return false
+    val receiverValue = getExplicitReceiverValue()?.let { DataFlowValueFactory.createDataFlowValue(it, context) }
+                        ?: return false
+    return context.dataFlowInfo.getPredictableNullability(receiverValue).canBeNull()
+}
+
+fun ResolvedCall<*>.makeNullableTypeIfSafeReceiver(type: KotlinType?, context: CallResolutionContext<*>) =
+        type?.let { TypeUtils.makeNullableIfNeeded(type, hasSafeNullableReceiver(context)) }
+
 fun ResolvedCall<*>.hasBothReceivers() = dispatchReceiver != null && extensionReceiver != null