Build fix: nullable exhaustiveness checker is now only a part of other exhaustiveness checkers

compiler/frontend/src/org/jetbrains/kotlin/cfg/WhenChecker.kt

@@ -72,12 +72,11 @@ private object NullMissingCase : WhenMissingCase {
     override val branchConditionText = "null"
 }
 
-private object WhenOnNullableExhaustivenessChecker : WhenExhaustivenessChecker {
-    override fun getMissingCases(expression: KtWhenExpression, context: BindingContext, subjectDescriptor: ClassDescriptor?, nullable: Boolean) =
+// It's not a regular exhaustiveness checker, invoke it only inside other checkers
+private object WhenOnNullableExhaustivenessChecker /* : WhenExhaustivenessChecker*/ {
+    fun getMissingCases(expression: KtWhenExpression, context: BindingContext, subjectDescriptor: ClassDescriptor?, nullable: Boolean) =
             if (nullable) getNullCaseIfMissing(expression, context) else listOf()
 
-    override fun isApplicable(subjectType: KotlinType): Boolean = TypeUtils.isNullableType(subjectType)
-
     private fun getNullCaseIfMissing(expression: KtWhenExpression, context: BindingContext): List<WhenMissingCase> {
         for (entry in expression.entries) {
             for (condition in entry.conditions) {
@@ -121,7 +120,8 @@ private object WhenOnBooleanExhaustivenessChecker : WhenExhaustivenessChecker {
             }
         }
         return (if (!containsTrue) listOf(BooleanMissingCase(true)) else listOf()) +
-               (if (!containsFalse) listOf(BooleanMissingCase(false)) else listOf())
+               (if (!containsFalse) listOf(BooleanMissingCase(false)) else listOf()) +
+               WhenOnNullableExhaustivenessChecker.getMissingCases(expression, context, subjectDescriptor, nullable)
     }
 
     override fun isApplicable(subjectType: KotlinType): Boolean {
@@ -210,7 +210,8 @@ private object WhenOnEnumExhaustivenessChecker : WhenOnClassExhaustivenessChecke
                         .filter { isEnumEntry(it) }
                         .filterIsInstance<ClassDescriptor>()
                         .toSet()
-        return getMissingClassCases(expression, entryDescriptors, context)
+        return getMissingClassCases(expression, entryDescriptors, context) +
+               WhenOnNullableExhaustivenessChecker.getMissingCases(expression, context, subjectDescriptor, nullable)
     }
 
     override fun isApplicable(subjectType: KotlinType): Boolean {
@@ -232,7 +233,8 @@ private object WhenOnSealedExhaustivenessChecker : WhenOnClassExhaustivenessChec
         val memberClassDescriptors = LinkedHashSet<ClassDescriptor>()
         collectNestedSubclasses(subjectDescriptor!!, subjectDescriptor, memberClassDescriptors)
         // When on a sealed class without derived members is considered non-exhaustive (see test WhenOnEmptySealed)
-        return getMissingClassCases(expression, memberClassDescriptors, context)
+        return getMissingClassCases(expression, memberClassDescriptors, context) +
+               WhenOnNullableExhaustivenessChecker.getMissingCases(expression, context, subjectDescriptor, nullable)
     }
 
     override fun isApplicable(subjectType: KotlinType): Boolean {
@@ -259,8 +261,7 @@ object WhenChecker {
 
     private val exhaustivenessCheckers = listOf(WhenOnBooleanExhaustivenessChecker,
                                                 WhenOnEnumExhaustivenessChecker,
-                                                WhenOnSealedExhaustivenessChecker,
-                                                WhenOnNullableExhaustivenessChecker)
+                                                WhenOnSealedExhaustivenessChecker)
 
     @JvmStatic
     fun getNecessaryCases(expression: KtWhenExpression, context: BindingContext) =

idea/testData/checker/WhenNonExhaustive.kt

@@ -6,6 +6,11 @@ fun nonExhaustiveBoolean(b: Boolean) = <error descr="[NO_ELSE_IN_WHEN] when expr
     false -> 0
 }
 
+fun nonExhaustiveNullableBoolean(b: Boolean?) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'null' branch or 'else' branch instead">when</error>(b) {
+    false -> 0
+    true -> 1
+}
+
 enum class Color { 
     RED,
     GREEN,
@@ -48,6 +53,11 @@ fun nonExhaustiveSealed(v: Variant) = <error descr="[NO_ELSE_IN_WHEN] when expre
     Variant.Singleton -> false
 }
 
+fun nonExhaustiveNullableSealed(v: Variant?) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'Another', 'null' branches or 'else' branch instead">when</error>(v) {
+    Variant.Singleton -> false
+    is Variant.Something -> true
+}
+
 sealed class Empty
 
 fun nonExhaustiveEmpty(e: Empty) = <error descr="[NO_ELSE_IN_WHEN] when expression must be exhaustive, add necessary 'else' branch">when</error>(<warning>e</warning>) {}