NI: do explicit incorporation of type of fixing type variable into other constraints

^KT-37380 Fixed

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

@@ -38,6 +38,9 @@ class ConstraintIncorporator(
         fun addNewIncorporatedConstraint(typeVariable: TypeVariableMarker, type: KotlinTypeMarker, constraintContext: ConstraintContext)
     }
 
+    fun incorporateIntoOtherConstraints(c: Context, typeVariable: TypeVariableMarker, constraint: Constraint) =
+        c.insideOtherConstraint(typeVariable, constraint)
+
     // \alpha is typeVariable, \beta -- other type variable registered in ConstraintStorage
     fun incorporate(c: Context, typeVariable: TypeVariableMarker, constraint: Constraint) {
         // we shouldn't incorporate recursive constraint -- It is too dangerous

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

@@ -19,8 +19,7 @@ package org.jetbrains.kotlin.resolve.calls.inference.components
 
 import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystemOperation
 import org.jetbrains.kotlin.resolve.calls.inference.model.*
-import org.jetbrains.kotlin.resolve.calls.inference.model.ConstraintKind.LOWER
+import org.jetbrains.kotlin.resolve.calls.inference.model.ConstraintKind.*
-import org.jetbrains.kotlin.resolve.calls.inference.model.ConstraintKind.UPPER
 import org.jetbrains.kotlin.resolve.calls.model.KotlinCallDiagnostic
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.checker.KotlinTypeRefiner
@@ -56,7 +55,7 @@ class ConstraintInjector(
     }
 
     fun addInitialEqualityConstraint(c: Context, a: KotlinTypeMarker, b: KotlinTypeMarker, position: ConstraintPosition) {
-        val initialConstraint = InitialConstraint(a, b, ConstraintKind.EQUALITY, position)
+        val initialConstraint = InitialConstraint(a, b, EQUALITY, position)
         c.addInitialConstraint(initialConstraint)
         updateAllowedTypeDepth(c, a)
         updateAllowedTypeDepth(c, b)
@@ -81,8 +80,11 @@ class ConstraintInjector(
         typeCheckerContext.runIsSubtypeOf(lowerType, upperType)
         var constraintsFromIsSubtype = true
 
-        while (possibleNewConstraints != null) {
+        if (incorporatePosition.from is FixVariableConstraintPosition && lowerType == incorporatePosition.initialConstraint.a) {
+            c.incorporateEqualityConstraintForFixingTypeVariable(incorporatePosition, typeCheckerContext)
+        }
 
+        while (possibleNewConstraints != null) {
             val constraintsToProcess = possibleNewConstraints
             possibleNewConstraints = null
             for ((typeVariable, constraint) in constraintsToProcess!!) {
@@ -103,7 +105,7 @@ class ConstraintInjector(
             if (possibleNewConstraints == null ||
                 (contextOps != null && c.notFixedTypeVariables.all { typeVariable ->
                     typeVariable.value.constraints.any { constraint ->
-                        constraint.kind == ConstraintKind.EQUALITY && contextOps.isProperType(constraint.type)
+                        constraint.kind == EQUALITY && contextOps.isProperType(constraint.type)
                     }
                 })
             ) {
@@ -117,6 +119,29 @@ class ConstraintInjector(
         c.maxTypeDepthFromInitialConstraints = max(c.maxTypeDepthFromInitialConstraints, initialType.typeDepth())
     }
 
+    private fun Context.incorporateEqualityConstraintForFixingTypeVariable(
+        incorporatePosition: IncorporationConstraintPosition,
+        typeCheckerContext: TypeCheckerContext
+    ) {
+        if (incorporatePosition.from !is FixVariableConstraintPosition) return
+
+        val typeToIncorporate = incorporatePosition.initialConstraint.b
+
+        if (typeToIncorporate.isUninferredParameter() || typeToIncorporate.isError()) return
+
+        constraintIncorporator.incorporateIntoOtherConstraints(
+            typeCheckerContext,
+            incorporatePosition.from.variable,
+            Constraint(
+                EQUALITY,
+                typeToIncorporate,
+                incorporatePosition,
+                derivedFrom = setOf(),
+                isNullabilityConstraint = false
+            )
+        )
+    }
+
     private fun Context.shouldWeSkipConstraint(
         typeVariable: TypeVariableMarker,
         constraint: Constraint,

compiler/testData/diagnostics/tests/inference/completion/postponedArgumentsAnalysis/lackOfDeepIncorporation.kt

@@ -30,7 +30,7 @@ class Foo<out A> {
             other1.product(
                 other2.product(
                     other3.product(
-                        <!TYPE_MISMATCH!>bar { d -> { c -> { b -> { a -> function(<!DEBUG_INFO_EXPRESSION_TYPE("A")!>a<!>, <!DEBUG_INFO_EXPRESSION_TYPE("B")!>b<!>, <!DEBUG_INFO_EXPRESSION_TYPE("C")!>c<!>, <!DEBUG_INFO_EXPRESSION_TYPE("D")!>d<!>) } } } }<!>
+                        bar { d -> { c -> { b -> { a -> function(<!DEBUG_INFO_EXPRESSION_TYPE("A")!>a<!>, <!DEBUG_INFO_EXPRESSION_TYPE("B")!>b<!>, <!DEBUG_INFO_EXPRESSION_TYPE("C")!>c<!>, <!DEBUG_INFO_EXPRESSION_TYPE("D")!>d<!>) } } } }
                     )
                 )
             )
@@ -43,9 +43,9 @@ class Foo<out A> {
             other1.product(
                 other2.product(
                     other3.product(
-                        <!TYPE_MISMATCH!>other4.product(
+                        other4.product(
                             bar { e -> { d -> { c -> { b -> { a -> function(<!DEBUG_INFO_EXPRESSION_TYPE("A")!>a<!>, <!DEBUG_INFO_EXPRESSION_TYPE("B")!>b<!>, <!DEBUG_INFO_EXPRESSION_TYPE("C")!>c<!>, <!DEBUG_INFO_EXPRESSION_TYPE("D")!>d<!>, <!DEBUG_INFO_EXPRESSION_TYPE("E")!>e<!>) } } } } }
-                        )<!>
+                        )
                     )
                 )
             )