FIR checker: report expression of nullable type parameter as LHS of class literals

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirGetClassCallChecker.kt

@@ -6,7 +6,9 @@
 package org.jetbrains.kotlin.fir.analysis.checkers.expression
 
 import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
+import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.isSubtypeOfAny
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
@@ -15,6 +17,7 @@ import org.jetbrains.kotlin.fir.declarations.FirTypeParameter
 import org.jetbrains.kotlin.fir.declarations.FirTypeParameterRefsOwner
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.references.FirResolvedNamedReference
+import org.jetbrains.kotlin.fir.scopes.impl.toConeType
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.lexer.KtTokens.QUEST
@@ -38,7 +41,8 @@ object FirGetClassCallChecker : FirBasicExpressionChecker() {
         val argument = expression.argument
         val isNullable = markedNullable ||
                 (argument as? FirResolvedQualifier)?.isNullableLHSForCallableReference == true ||
-                argument.typeRef.coneType.isMarkedNullable
+                argument.typeRef.coneType.isMarkedNullable ||
+                argument.typeRef.coneType.isNullableTypeParameter(context.session)
         if (isNullable) {
             if (argument.canBeDoubleColonLHSAsType) {
                 reporter.reportOn(source, FirErrors.NULLABLE_TYPE_IN_CLASS_LITERAL_LHS, context)
@@ -74,6 +78,14 @@ object FirGetClassCallChecker : FirBasicExpressionChecker() {
         }
     }
 
+    private fun ConeKotlinType.isNullableTypeParameter(session: FirSession): Boolean {
+        if (this !is ConeTypeParameterType) return false
+        val typeParameter = lookupTag.typeParameterSymbol.fir
+        return !typeParameter.isReified &&
+                // E.g., fun <T> f2(t: T): Any = t::class
+                !typeParameter.toConeType().isSubtypeOfAny(session)
+    }
+
     private val FirExpression.canBeDoubleColonLHSAsType: Boolean
         get() {
             return this is FirResolvedQualifier ||

compiler/testData/diagnostics/tests/classLiteral/expressionWithNullableType.fir.kt

@@ -1,15 +0,0 @@
-// FILE: J.java
-
-public interface J {
-    String platformString();
-}
-
-// FILE: test.kt
-
-fun f1(x: Int?): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>x<!>::class
-fun <T> f2(t: T): Any = t::class
-fun <S : String?> f3(s: S): Any = s::class
-fun <U : Any> f4(u: U?): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>u<!>::class
-fun f5(c: List<*>): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>c[0]<!>::class
-
-fun f6(j: J): Any = j.platformString()::class

compiler/testData/diagnostics/tests/classLiteral/expressionWithNullableType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // FILE: J.java
 
 public interface J {
@@ -8,6 +9,7 @@ public interface J {
 
 fun f1(x: Int?): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>x<!>::class
 fun <T> f2(t: T): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>t<!>::class
+fun <T> f21(t: T): Any where T : Any?, T : Comparable<T> = t::class
 fun <S : String?> f3(s: S): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>s<!>::class
 fun <U : Any> f4(u: U?): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>u<!>::class
 fun f5(c: List<*>): Any = <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>c[0]<!>::class

compiler/testData/diagnostics/tests/classLiteral/expressionWithNullableType.txt

@@ -2,6 +2,7 @@ package
 
 public fun f1(/*0*/ x: kotlin.Int?): kotlin.Any
 public fun </*0*/ T> f2(/*0*/ t: T): kotlin.Any
+public fun </*0*/ T> f21(/*0*/ t: T): kotlin.Any where T : kotlin.Comparable<T>
 public fun </*0*/ S : kotlin.String?> f3(/*0*/ s: S): kotlin.Any
 public fun </*0*/ U : kotlin.Any> f4(/*0*/ u: U?): kotlin.Any
 public fun f5(/*0*/ c: kotlin.collections.List<*>): kotlin.Any