[FE] Don't check intersection emptiness if there were lower constraints

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/ResolutionStages.kt

@@ -583,7 +583,11 @@ internal object CheckIncompatibleTypeVariableUpperBounds : ResolutionStage() {
             for (variableWithConstraints in candidate.system.notFixedTypeVariables.values) {
                 val upperTypes = variableWithConstraints.constraints.extractUpperTypesToCheckIntersectionEmptiness()
 
-                if (upperTypes.computeEmptyIntersectionTypeKind().isDefinitelyEmpty()) {
+                // TODO: consider reporting errors on bounded type variables by incompatible types but with other lower constraints
+                if (
+                    variableWithConstraints.constraints.none { it.kind.isLower() }
+                    && upperTypes.computeEmptyIntersectionTypeKind().isDefinitelyEmpty()
+                ) {
                     sink.yieldDiagnostic(
                         @Suppress("UNCHECKED_CAST")
                         InferredEmptyIntersectionDiagnostic(

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

@@ -892,7 +892,11 @@ internal object CheckIncompatibleTypeVariableUpperBounds : ResolutionPart() {
         for (variableWithConstraints in getSystem().getBuilder().currentStorage().notFixedTypeVariables.values) {
             val upperTypes = variableWithConstraints.constraints.extractUpperTypesToCheckIntersectionEmptiness()
 
-            if (upperTypes.computeEmptyIntersectionTypeKind().isDefinitelyEmpty()) {
+            // TODO: consider reporting errors on bounded type variables by incompatible types but with other lower constraints
+            if (
+                variableWithConstraints.constraints.none { it.kind.isLower() }
+                && upperTypes.computeEmptyIntersectionTypeKind().isDefinitelyEmpty()
+            ) {
                 val isInferredEmptyIntersectionForbidden =
                     callComponents.languageVersionSettings.supportsFeature(LanguageFeature.ForbidInferringTypeVariablesIntoEmptyIntersection)
 

compiler/testData/diagnostics/tests/inference/emptyIntersectionTypes/contravariance.fir.kt

@@ -1,9 +0,0 @@
-// WITH_STDLIB
-
-fun expandMaskConditionsAndUpdateVariableNodes(validOffsets: Collection<Int>) {}
-
-fun main(x: List<Int>, y: Int) {
-    <!INFERRED_TYPE_VARIABLE_INTO_EMPTY_INTERSECTION!>expandMaskConditionsAndUpdateVariableNodes<!>(
-        x.mapTo(mutableSetOf()) { y }
-    )
-}

compiler/testData/diagnostics/tests/inference/emptyIntersectionTypes/contravariance.kt

@@ -1,9 +1,10 @@
+// FIR_IDENTICAL
 // WITH_STDLIB
 
 fun expandMaskConditionsAndUpdateVariableNodes(validOffsets: Collection<Int>) {}
 
 fun main(x: List<Int>, y: Int) {
-    <!INFERRED_TYPE_VARIABLE_INTO_EMPTY_INTERSECTION_WARNING!>expandMaskConditionsAndUpdateVariableNodes<!>(
+    expandMaskConditionsAndUpdateVariableNodes(
         x.mapTo(mutableSetOf()) { y }
     )
 }

core/compiler.common/src/org/jetbrains/kotlin/types/EmptyIntersectionTypeKind.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.types
 
-enum class EmptyIntersectionTypeKind { NOT_EMPTY_INTERSECTION, MULTIPLE_CLASSES } // TODO: add `SINGLE_FINAL_CLASS` later
+// TODO: add `SINGLE_FINAL_CLASS` later to report warnings
+enum class EmptyIntersectionTypeKind { NOT_EMPTY_INTERSECTION, MULTIPLE_CLASSES }
 
 fun EmptyIntersectionTypeKind.isDefinitelyEmpty(): Boolean = this == EmptyIntersectionTypeKind.MULTIPLE_CLASSES