From 4cdddb1b08ad9bb3ec476a4b14c08dd4070424c4 Mon Sep 17 00:00:00 2001
From: Nikolay Lunyak <nikolay.lunyak@jetbrains.com>
Date: Thu, 29 Feb 2024 16:01:42 +0200
Subject: [PATCH] [FIR] Unify checks for `is` and `as`

---
 .../expression/FirCastOperatorsChecker.kt     | 34 +++++++++++--------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirCastOperatorsChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirCastOperatorsChecker.kt
index 2a204a07336..c24d0f6457f 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirCastOperatorsChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirCastOperatorsChecker.kt
@@ -45,26 +45,14 @@ object FirCastOperatorsChecker : FirTypeOperatorCallChecker(MppCheckerKind.Commo
         }
     }
 
-    private fun checkIsApplicability(l: TypeInfo, r: TypeInfo, expression: FirTypeOperatorCall, context: CheckerContext): Applicability {
-        val oneIsFinal = l.isFinal || r.isFinal
-        val oneIsNotNull = !l.type.isNullable || !r.type.isNullable
-
-        return when {
-            isRefinementUseless(context, l.directType.upperBoundIfFlexible(), r.directType, expression) -> Applicability.USELESS_IS_CHECK
-            isCastErased(l.directType, r.directType, context) -> Applicability.CAST_ERASED
-            oneIsNotNull && oneIsFinal && areUnrelated(l, r, context) -> Applicability.IMPOSSIBLE_IS_CHECK
-            else -> Applicability.APPLICABLE
-        }
-    }
+    private fun checkIsApplicability(l: TypeInfo, r: TypeInfo, expression: FirTypeOperatorCall, context: CheckerContext): Applicability =
+        checkAnyApplicability(l, r, expression, Applicability.IMPOSSIBLE_IS_CHECK, Applicability.USELESS_IS_CHECK, context)
 
     private fun checkAsApplicability(l: TypeInfo, r: TypeInfo, expression: FirTypeOperatorCall, context: CheckerContext): Applicability {
-        val oneIsFinal = l.isFinal || r.isFinal
-        val oneIsNotNull = !l.type.isNullable || !r.type.isNullable
         val isNullableNothingWithNotNull = !l.type.isNullable && r.type.isNullableNothing
                 || l.type.isNullableNothing && !r.type.isNullable
 
         return when {
-            isRefinementUseless(context, l.directType.upperBoundIfFlexible(), r.directType, expression) -> Applicability.USELESS_CAST
             l.type.isNothing && r.type.isNothingOrNullableNothing -> Applicability.APPLICABLE
             r.type.isNothing -> Applicability.IMPOSSIBLE_CAST
             isNullableNothingWithNotNull -> when (expression.operation) {
@@ -72,7 +60,23 @@ object FirCastOperatorsChecker : FirTypeOperatorCallChecker(MppCheckerKind.Commo
                 FirOperation.SAFE_AS -> Applicability.USELESS_CAST
                 else -> Applicability.IMPOSSIBLE_CAST
             }
-            oneIsNotNull && oneIsFinal && areUnrelated(l, r, context) -> Applicability.IMPOSSIBLE_CAST
+            else -> checkAnyApplicability(l, r, expression, Applicability.IMPOSSIBLE_CAST, Applicability.USELESS_CAST, context)
+        }
+    }
+
+    private fun checkAnyApplicability(
+        l: TypeInfo, r: TypeInfo,
+        expression: FirTypeOperatorCall,
+        impossible: Applicability,
+        useless: Applicability,
+        context: CheckerContext,
+    ): Applicability {
+        val oneIsFinal = l.isFinal || r.isFinal
+        val oneIsNotNull = !l.type.isNullable || !r.type.isNullable
+
+        return when {
+            isRefinementUseless(context, l.directType.upperBoundIfFlexible(), r.directType, expression) -> useless
+            oneIsNotNull && oneIsFinal && areUnrelated(l, r, context) -> impossible
             isCastErased(l.directType, r.directType, context) -> Applicability.CAST_ERASED
             else -> Applicability.APPLICABLE
         }