[NI] Don't loose diagnostic after type variable fixation

#KT-24488 Fixed

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

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.resolve.calls.inference.NewConstraintSystem
 import org.jetbrains.kotlin.resolve.calls.inference.addSubtypeConstraintIfCompatible
 import org.jetbrains.kotlin.resolve.calls.inference.components.KotlinConstraintSystemCompleter
 import org.jetbrains.kotlin.resolve.calls.inference.components.KotlinConstraintSystemCompleter.ConstraintSystemCompletionMode
+import org.jetbrains.kotlin.resolve.calls.inference.model.Constraint
 import org.jetbrains.kotlin.resolve.calls.inference.model.ConstraintStorage.Empty.hasContradiction
 import org.jetbrains.kotlin.resolve.calls.inference.model.ExpectedTypeConstraintPosition
 import org.jetbrains.kotlin.resolve.calls.model.*
@@ -19,6 +20,7 @@ import org.jetbrains.kotlin.types.ErrorUtils
 import org.jetbrains.kotlin.types.TypeUtils
 import org.jetbrains.kotlin.types.UnwrappedType
 import org.jetbrains.kotlin.types.model.TypeSystemInferenceExtensionContext
+import org.jetbrains.kotlin.types.model.defaultType
 import org.jetbrains.kotlin.types.model.isIntegerLiteralTypeConstructor
 import org.jetbrains.kotlin.types.model.typeConstructor
 import org.jetbrains.kotlin.types.typeUtil.contains

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

@@ -41,7 +41,7 @@ class KotlinConstraintSystemCompleter(
         // mutable operations
         fun addError(error: KotlinCallDiagnostic)
 
-        fun fixVariable(variable: TypeVariableMarker, resultType: KotlinTypeMarker)
+        fun fixVariable(variable: TypeVariableMarker, resultType: KotlinTypeMarker, atom: ResolvedAtom?)
     }
 
     fun runCompletion(
@@ -87,7 +87,7 @@ class KotlinConstraintSystemCompleter(
                 val variableWithConstraints = c.notFixedTypeVariables.getValue(variableForFixation.variable)
 
                 if (variableForFixation.hasProperConstraint)
-                    fixVariable(c, topLevelType, variableWithConstraints, postponedKtPrimitives)
+                    fixVariable(c, topLevelType, variableWithConstraints, postponedKtPrimitives, topLevelAtoms)
                 else
                     processVariableWhenNotEnoughInformation(c, variableWithConstraints, topLevelAtoms)
 
@@ -206,19 +206,22 @@ class KotlinConstraintSystemCompleter(
         c: Context,
         topLevelType: UnwrappedType,
         variableWithConstraints: VariableWithConstraints,
-        postponedResolveKtPrimitives: List<PostponedResolvedAtom>
+        postponedResolveKtPrimitives: List<PostponedResolvedAtom>,
+        topLevelAtoms: List<ResolvedAtom>
     ) {
         val direction = TypeVariableDirectionCalculator(c, postponedResolveKtPrimitives, topLevelType).getDirection(variableWithConstraints)
-        fixVariable(c, variableWithConstraints, direction)
+        fixVariable(c, variableWithConstraints, direction, topLevelAtoms)
     }
 
     fun fixVariable(
         c: Context,
         variableWithConstraints: VariableWithConstraints,
-        direction: TypeVariableDirectionCalculator.ResolveDirection
+        direction: TypeVariableDirectionCalculator.ResolveDirection,
+        topLevelAtoms: List<ResolvedAtom>
     ) {
         val resultType = resultTypeResolver.findResultType(c, variableWithConstraints, direction)
-        c.fixVariable(variableWithConstraints.typeVariable, resultType)
+        val resolvedAtom = findResolvedAtomBy(variableWithConstraints.typeVariable, topLevelAtoms) ?: topLevelAtoms.firstOrNull()
+        c.fixVariable(variableWithConstraints.typeVariable, resultType, resolvedAtom)
     }
 
     private fun processVariableWhenNotEnoughInformation(
@@ -238,7 +241,7 @@ class KotlinConstraintSystemCompleter(
         else
             ErrorUtils.createErrorType("Cannot infer type variable $typeVariable")
 
-        c.fixVariable(typeVariable, resultErrorType)
+        c.fixVariable(typeVariable, resultErrorType, resolvedAtom)
     }
 
     private fun findResolvedAtomBy(typeVariable: TypeVariableMarker, topLevelAtoms: List<ResolvedAtom>): ResolvedAtom? {

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

@@ -53,7 +53,7 @@ class ReceiverConstraintPosition(val argument: KotlinCallArgument) : ConstraintP
     override fun toString() = "Receiver $argument"
 }
 
-class FixVariableConstraintPosition(val variable: TypeVariableMarker) : ConstraintPosition() {
+class FixVariableConstraintPosition(val variable: TypeVariableMarker, val resolvedAtom: ResolvedAtom?) : ConstraintPosition() {
     override fun toString() = "Fix variable $variable"
 }
 

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

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.resolve.calls.inference.components.KotlinConstraintS
 import org.jetbrains.kotlin.resolve.calls.inference.components.ResultTypeResolver
 import org.jetbrains.kotlin.resolve.calls.model.KotlinCallDiagnostic
 import org.jetbrains.kotlin.resolve.calls.model.OnlyInputTypesDiagnostic
+import org.jetbrains.kotlin.resolve.calls.model.ResolvedAtom
 import org.jetbrains.kotlin.types.IntersectionTypeConstructor
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.checker.NewKotlinTypeChecker
@@ -247,10 +248,13 @@ class NewConstraintSystemImpl(
     }
 
     // KotlinConstraintSystemCompleter.Context
-    override fun fixVariable(variable: TypeVariableMarker, resultType: KotlinTypeMarker) {
+    override fun fixVariable(variable: TypeVariableMarker, resultType: KotlinTypeMarker, atom: ResolvedAtom?) {
         checkState(State.BUILDING, State.COMPLETION)
 
-        constraintInjector.addInitialEqualityConstraint(this, variable.defaultType(), resultType, FixVariableConstraintPosition(variable))
+        constraintInjector.addInitialEqualityConstraint(
+            this, variable.defaultType(), resultType, FixVariableConstraintPosition(variable, atom)
+        )
+
         val variableWithConstraints = notFixedTypeVariables.remove(variable.freshTypeConstructor())
         checkOnlyInputTypesAnnotation(variableWithConstraints, resultType)