[FIR] Report missing NO_ELSE_IN_WHEN for when statement with expect enums and sealed classes

^KT-59404 Fixed

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirWhenExhaustivenessTransformer.kt

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.diagnostics.WhenMissingCase
 import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.declarations.utils.isExpect
 import org.jetbrains.kotlin.fir.declarations.utils.modality
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.expressions.impl.FirElseIfTrueCondition
@@ -120,19 +121,21 @@ class FirWhenExhaustivenessTransformer(private val bodyResolveComponents: BodyRe
             return
         }
 
-        val unwrappedIntersectionTypes = subjectType.unwrapIntersectionType()
-
         var status: ExhaustivenessStatus = ExhaustivenessStatus.NotExhaustive.NO_ELSE_BRANCH
 
-        for (unwrappedSubjectType in unwrappedIntersectionTypes) {
-            val localStatus = computeStatusForNonIntersectionType(unwrappedSubjectType, session, whenExpression)
-            when {
-                localStatus === ExhaustivenessStatus.ProperlyExhaustive -> {
-                    status = localStatus
-                    break
-                }
-                localStatus !== ExhaustivenessStatus.NotExhaustive.NO_ELSE_BRANCH && status === ExhaustivenessStatus.NotExhaustive.NO_ELSE_BRANCH -> {
-                    status = localStatus
+        if (subjectType.toRegularClassSymbol(session)?.isExpect != true) {
+            val unwrappedIntersectionTypes = subjectType.unwrapIntersectionType()
+
+            for (unwrappedSubjectType in unwrappedIntersectionTypes) {
+                val localStatus = computeStatusForNonIntersectionType(unwrappedSubjectType, session, whenExpression)
+                when {
+                    localStatus === ExhaustivenessStatus.ProperlyExhaustive -> {
+                        status = localStatus
+                        break
+                    }
+                    localStatus !== ExhaustivenessStatus.NotExhaustive.NO_ELSE_BRANCH && status === ExhaustivenessStatus.NotExhaustive.NO_ELSE_BRANCH -> {
+                        status = localStatus
+                    }
                 }
             }
         }

compiler/testData/diagnostics/tests/multiplatform/exhaustiveness/expectEnum.fir.kt

@@ -8,7 +8,7 @@ expect enum class Base {
 }
 
 fun testCommon(base: Base) {
-    val x = when (base) { // must be an error
+    val x = <!NO_ELSE_IN_WHEN!>when<!> (base) { // must be an error
         Base.A -> 1
         Base.B -> 2
     }

compiler/testData/diagnostics/tests/multiplatform/exhaustiveness/expectSealedClass.fir.kt

@@ -9,7 +9,7 @@ class A : Base()
 object B : Base()
 
 fun testCommon(base: Base) {
-    val x = when (base) { // must be an error
+    val x = <!NO_ELSE_IN_WHEN!>when<!> (base) { // must be an error
         is A -> 1
         B -> 2
     }

compiler/testData/diagnostics/tests/multiplatform/exhaustiveness/expectSealedInterface.fir.kt

@@ -9,7 +9,7 @@ class A : Base
 object B : Base
 
 fun testCommon(base: Base) {
-    val x = when (base) { // must be an error
+    val x = <!NO_ELSE_IN_WHEN!>when<!> (base) { // must be an error
         is A -> 1
         B -> 2
     }

compiler/testData/diagnostics/tests/multiplatform/exhaustiveness/kt45796.fir.kt

@@ -8,7 +8,7 @@ expect sealed class SealedClass() {
 }
 
 fun whenForExpectSealed(s: SealedClass): Int {
-    return when (s) { // should be error, because actual sealed class may add more implementations
+    return <!NO_ELSE_IN_WHEN!>when<!> (s) { // should be error, because actual sealed class may add more implementations
         is SealedClass.Nested.NestedDeeper -> 7
         is SealedClass.Nested -> 8
     }