[NI] Remove lambda coersion to Unit in case of error return type(s)

Coersion to Unit from error type leads to misleading type mismatches:
"expected <expected lambda return type> found Unit", despite no user-provided Unit / empty lambda.
These diagnostics were collected, but not reported before, and that had been disguising the issue for a while.

KT-34729 Fixed

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/ExternalComponents.kt

@@ -12,7 +12,6 @@ import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
-import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.calls.inference.components.ConstraintInjector
 import org.jetbrains.kotlin.resolve.calls.inference.model.NewTypeVariable
 import org.jetbrains.kotlin.resolve.calls.model.*
@@ -42,6 +41,16 @@ interface KotlinResolutionStatelessCallbacks {
     ): SimpleConstraintSystem
 }
 
+data class ReturnArgumentsInfo(
+    val nonErrorArguments: List<KotlinCallArgument>,
+    val returnArgumentsExist: Boolean
+)
+
+data class ReturnArgumentsAnalysisResult(
+    val returnArgumentsInfo: ReturnArgumentsInfo,
+    val inferenceSession: InferenceSession?
+)
+
 // This components hold state (trace). Work with this carefully.
 interface KotlinResolutionCallbacks {
     fun analyzeAndGetLambdaReturnArguments(
@@ -52,7 +61,7 @@ interface KotlinResolutionCallbacks {
         expectedReturnType: UnwrappedType?, // null means, that return type is not proper i.e. it depends on some type variables
         annotations: Annotations,
         stubsForPostponedVariables: Map<NewTypeVariable, StubType>
-    ): Pair<List<KotlinCallArgument>, InferenceSession?>
+    ): ReturnArgumentsAnalysisResult
 
     fun bindStubResolvedCallForCandidate(candidate: ResolvedCallAtom)
 

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/components/PostponedArgumentsAnalyzer.kt

@@ -118,7 +118,7 @@ class PostponedArgumentsAnalyzer(
             else FilteredAnnotations(annotations, true) { it != KotlinBuiltIns.FQ_NAMES.extensionFunctionType }
         }
 
-        val (returnArguments, inferenceSession) = resolutionCallbacks.analyzeAndGetLambdaReturnArguments(
+        val (returnArgumentsInfo, inferenceSession) = resolutionCallbacks.analyzeAndGetLambdaReturnArguments(
             lambda.atom,
             lambda.isSuspend,
             receiver,
@@ -128,21 +128,21 @@ class PostponedArgumentsAnalyzer(
             stubsForPostponedVariables.cast()
         )
 
-        returnArguments.forEach { c.addSubsystemFromArgument(it) }
+        returnArgumentsInfo.nonErrorArguments.forEach { c.addSubsystemFromArgument(it) }
 
-        val subResolvedKtPrimitives = returnArguments.map {
+        val subResolvedKtPrimitives = returnArgumentsInfo.nonErrorArguments.map {
             resolveKtPrimitive(
                 c.getBuilder(), it, lambda.returnType.let(::substitute), diagnosticHolder, isReceiver = false
             )
         }
 
-        if (returnArguments.isEmpty()) {
+        if (!returnArgumentsInfo.returnArgumentsExist) {
             val unitType = lambda.returnType.builtIns.unitType
             val lambdaReturnType = lambda.returnType.let(::substitute)
             c.getBuilder().addSubtypeConstraint(unitType, lambdaReturnType, LambdaArgumentConstraintPosition(lambda))
         }
 
-        lambda.setAnalyzedResults(returnArguments, subResolvedKtPrimitives)
+        lambda.setAnalyzedResults(returnArgumentsInfo, subResolvedKtPrimitives)
 
         if (inferenceSession != null) {
             val storageSnapshot = c.getBuilder().currentStorage()

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/model/ResolutionAtoms.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.resolve.calls.model
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
 import org.jetbrains.kotlin.resolve.calls.components.CallableReferenceCandidate
+import org.jetbrains.kotlin.resolve.calls.components.ReturnArgumentsInfo
 import org.jetbrains.kotlin.resolve.calls.components.TypeArgumentsToParametersMapper
 import org.jetbrains.kotlin.resolve.calls.components.extractInputOutputTypesFromCallableReferenceExpectedType
 import org.jetbrains.kotlin.resolve.calls.inference.components.FreshVariableNewTypeSubstitutor
@@ -115,14 +116,14 @@ class ResolvedLambdaAtom(
     val typeVariableForLambdaReturnType: TypeVariableForLambdaReturnType?,
     override val expectedType: UnwrappedType?
 ) : PostponedResolvedAtom() {
-    lateinit var resultArguments: List<KotlinCallArgument>
+    lateinit var resultArgumentsInfo: ReturnArgumentsInfo
         private set
 
     fun setAnalyzedResults(
-        resultArguments: List<KotlinCallArgument>,
+        resultArguments: ReturnArgumentsInfo,
         subResolvedAtoms: List<ResolvedAtom>
     ) {
-        this.resultArguments = resultArguments
+        this.resultArgumentsInfo = resultArguments
         setAnalyzedResults(subResolvedAtoms)
     }