[FIR] Report CANNOT_CHECK_FOR_ERASED independent of reified parameters

This changes the logic so that Foo<T> is reported no matter if T is
reified or not. Even for Array<reified T> to align K2 with K1 logic.

#KT-55903 Fixed

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirCastDiagnosticsHelpers.kt

@@ -141,12 +141,11 @@ fun isCastErased(supertype: ConeKotlinType, subtype: ConeKotlinType, context: Ch
 
     // downcasting to a non-reified type parameter is always erased
     if (isNonReifiedTypeParameter) return true
+    // downcasting to a reified type parameter is never erased
+    else if (subtype is ConeTypeParameterType) return false
 
-    // Check that we are actually casting to a generic type
+    val regularClassSymbol = subtype.toRegularClassSymbol(context.session) ?: return true
-    // NOTE: this does not account for 'as Array<List<T>>'
+    val staticallyKnownSubtype = findStaticallyKnownSubtype(supertype, regularClassSymbol, context)
-    if (subtype.allParameterReified()) return false
-
-    val staticallyKnownSubtype = findStaticallyKnownSubtype(supertype, subtype, context)
 
     // If the substitution failed, it means that the result is an impossible type, e.g. something like Out<in Foo>
     // In this case, we can't guarantee anything, so the cast is considered to be erased
@@ -156,10 +155,6 @@ fun isCastErased(supertype: ConeKotlinType, subtype: ConeKotlinType, context: Ch
     return !AbstractTypeChecker.isSubtypeOf(context.session.typeContext, staticallyKnownSubtype, subtype, stubTypesEqualToAnything = false)
 }
 
-private fun ConeKotlinType.allParameterReified(): Boolean {
-    return typeArguments.all { (it.type as? ConeTypeParameterType)?.lookupTag?.typeParameterSymbol?.isReified == true }
-}
-
 /**
  * Remember that we are trying to cast something of type `supertype` to `subtype`.
 
@@ -178,7 +173,7 @@ private fun ConeKotlinType.allParameterReified(): Boolean {
  */
 fun findStaticallyKnownSubtype(
     supertype: ConeKotlinType,
-    subtype: ConeKotlinType,
+    subTypeClassSymbol: FirRegularClassSymbol,
     context: CheckerContext
 ): ConeKotlinType {
     assert(!supertype.isMarkedNullable) { "This method only makes sense for non-nullable types" }
@@ -188,8 +183,7 @@ fun findStaticallyKnownSubtype(
 
     // Assume we are casting an expression of type Collection<Foo> to List<Bar>
     // First, let's make List<T>, where T is a type variable
-    val subtypeWithVariables = subtype.toRegularClassSymbol(session)!!
+    val subtypeWithVariablesType = subTypeClassSymbol.defaultType()
-    val subtypeWithVariablesType = subtypeWithVariables.defaultType()
 
     // Now, let's find a supertype of List<T> that is a Collection of something,
     // in this case it will be Collection<T>
@@ -214,7 +208,7 @@ fun findStaticallyKnownSubtype(
                 normalizedType.typeConstructor(typeContext)
             ).firstOrNull()
 
-        val variables: List<FirTypeParameterSymbol> = subtypeWithVariables.typeParameterSymbols
+        val variables: List<FirTypeParameterSymbol> = subTypeClassSymbol.typeParameterSymbols
 
         val substitution = if (supertypeWithVariables != null) {
             // Now, let's try to unify Collection<T> and Collection<Foo> solution is a map from T to Foo

compiler/testData/diagnostics/tests/cast/IsErasedUpcastToNonReified.fir.kt

@@ -15,10 +15,25 @@ fun <T, S : T> test(x: T?, y: S, z: T) {
     null <!UNCHECKED_CAST!>as S<!>
 }
 
-inline fun <reified T> test(x: T?) {
+class Box<T>
+
+inline fun <reified T> test(x: T?, a: Any) {
     x is T
     null as T
     null as T?
+
+    a is T
+    a as T
+
+    a is <!CANNOT_CHECK_FOR_ERASED!>Box<T><!>
+    a is <!CANNOT_CHECK_FOR_ERASED!>Array<T><!>
+    a <!UNCHECKED_CAST!>as Box<T><!>
+    a <!UNCHECKED_CAST!>as Array<T><!>
+
+    a is <!CANNOT_CHECK_FOR_ERASED!>Box<List<T>><!>
+    a is <!CANNOT_CHECK_FOR_ERASED!>Array<List<T>><!>
+    a <!UNCHECKED_CAST!>as Box<List<T>><!>
+    a <!UNCHECKED_CAST!>as Array<List<T>><!>
 }
 
 fun <T> foo(x: List<T>, y: List<T>?) {

compiler/testData/diagnostics/tests/cast/IsErasedUpcastToNonReified.kt

@@ -15,13 +15,28 @@ fun <T, S : T> test(x: T?, y: S, z: T) {
     null <!UNCHECKED_CAST!>as S<!>
 }
 
-inline fun <reified T> test(x: T?) {
+class Box<T>
+
+inline fun <reified T> test(x: T?, a: Any) {
     x is T
     null as T
     null <!USELESS_CAST!>as T?<!>
+
+    a is T
+    a as T
+
+    a is <!CANNOT_CHECK_FOR_ERASED!>Box<T><!>
+    a is <!CANNOT_CHECK_FOR_ERASED!>Array<T><!>
+    a <!UNCHECKED_CAST!>as Box<T><!>
+    a <!UNCHECKED_CAST!>as Array<T><!>
+
+    a is <!CANNOT_CHECK_FOR_ERASED!>Box<List<T>><!>
+    a is <!CANNOT_CHECK_FOR_ERASED!>Array<List<T>><!>
+    a <!UNCHECKED_CAST!>as Box<List<T>><!>
+    a <!UNCHECKED_CAST!>as Array<List<T>><!>
 }
 
 fun <T> foo(x: List<T>, y: List<T>?) {
     <!USELESS_IS_CHECK!>x is List<T><!>
     y is List<T>
-}
+}

compiler/testData/diagnostics/tests/cast/IsErasedUpcastToNonReified.txt

@@ -1,5 +1,13 @@
 package
 
 public fun </*0*/ T> foo(/*0*/ x: kotlin.collections.List<T>, /*1*/ y: kotlin.collections.List<T>?): kotlin.Unit
-public inline fun </*0*/ reified T> test(/*0*/ x: T?): kotlin.Unit
 public fun </*0*/ T, /*1*/ S : T> test(/*0*/ x: T?, /*1*/ y: S, /*2*/ z: T): kotlin.Unit
+public inline fun </*0*/ reified T> test(/*0*/ x: T?, /*1*/ a: kotlin.Any): kotlin.Unit
+
+public final class Box</*0*/ T> {
+    public constructor Box</*0*/ T>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+