[FE 1.0] Introduce builder inference stub types checker which may report more precise and clear errors due to resolution ambiguity

^KT-49828 Fixed

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

@@ -78,14 +78,14 @@ class ClassicTypeSystemContextForCS(
 
     override fun createStubTypeForBuilderInference(typeVariable: TypeVariableMarker): StubTypeMarker {
         return StubTypeForBuilderInference(
-            typeVariable.freshTypeConstructor() as TypeConstructor,
+            typeVariable.freshTypeConstructor() as NewTypeVariableConstructor,
             typeVariable.defaultType().isMarkedNullable()
         )
     }
 
     override fun createStubTypeForTypeVariablesInSubtyping(typeVariable: TypeVariableMarker): StubTypeMarker {
         return StubTypeForTypeVariablesInSubtyping(
-            typeVariable.freshTypeConstructor() as TypeConstructor,
+            typeVariable.freshTypeConstructor() as NewTypeVariableConstructor,
             typeVariable.defaultType().isMarkedNullable()
         )
     }

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

@@ -34,8 +34,7 @@ class TypeVariableTypeConstructor(
     private val builtIns: KotlinBuiltIns,
     val debugName: String,
     override val originalTypeParameter: TypeParameterDescriptor?
-) : TypeConstructor,
-    NewTypeVariableConstructor, TypeVariableTypeConstructorMarker {
+) : NewTypeVariableConstructor, TypeVariableTypeConstructorMarker {
     override fun getParameters(): List<TypeParameterDescriptor> = emptyList()
     override fun getSupertypes(): Collection<KotlinType> = emptyList()
     override fun isFinal(): Boolean = false

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

@@ -59,11 +59,11 @@ interface LambdaKotlinCallArgument : PostponableKotlinCallArgument {
      */
     var hasBuilderInferenceAnnotation: Boolean
         get() = false
-        set(@Suppress("UNUSED_PARAMETER") value) {}
+        set(_) {}
 
     var builderInferenceSession: InferenceSession?
         get() = null
-        set(@Suppress("UNUSED_PARAMETER") value) {}
+        set(_) {}
 
     /**
      * parametersTypes == null means, that there is no declared arguments

compiler/resolution/src/org/jetbrains/kotlin/util/InferenceUtils.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.util
+
+import org.jetbrains.kotlin.resolve.calls.components.KotlinResolutionCallbacks
+import org.jetbrains.kotlin.resolve.calls.inference.NewConstraintSystem
+import org.jetbrains.kotlin.resolve.calls.inference.model.TypeVariableTypeConstructor
+import org.jetbrains.kotlin.resolve.calls.inference.model.typeForTypeVariable
+import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
+
+fun NewConstraintSystem.buildNotFixedVariablesToPossibleResultType(resolutionCallbacks: KotlinResolutionCallbacks): TypeSubstitutorMarker =
+    asConstraintSystemCompleterContext().typeSubstitutorByTypeConstructor(
+        getBuilder().currentStorage().notFixedTypeVariables.mapValues {
+            val typeVariable = it.key as TypeVariableTypeConstructor
+            resolutionCallbacks.findResultType(this, typeVariable) ?: typeVariable.typeForTypeVariable()
+        }
+)