FIR checker: report TYPE_PARAMETER_AS_REIFIED

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -8,7 +8,6 @@ package org.jetbrains.kotlin.fir.checkers.generator.diagnostics
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiTypeElement
 import org.jetbrains.kotlin.contracts.description.EventOccurrencesRange
-import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.diagnostics.WhenMissingCase
 import org.jetbrains.kotlin.resolve.ForbiddenNamedArgumentsTarget
@@ -18,6 +17,7 @@ import org.jetbrains.kotlin.fir.PrivateForInline
 import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
 import org.jetbrains.kotlin.fir.declarations.FirClass
 import org.jetbrains.kotlin.fir.declarations.FirMemberDeclaration
+import org.jetbrains.kotlin.fir.declarations.FirTypeParameter
 import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
@@ -27,7 +27,6 @@ import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.*
-import org.jetbrains.kotlin.types.KotlinType
 
 
 @Suppress("UNUSED_VARIABLE", "LocalVariableName", "ClassName", "unused")
@@ -247,6 +246,10 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
         val TYPE_PARAMETER_IN_CATCH_CLAUSE by error<FirSourceElement, PsiElement>()
         val GENERIC_THROWABLE_SUBCLASS by error<FirSourceElement, KtTypeParameterList>()
         val INNER_CLASS_OF_GENERIC_THROWABLE_SUBCLASS by error<FirSourceElement, KtClassOrObject>(PositioningStrategy.DECLARATION_NAME)
+
+        val TYPE_PARAMETER_AS_REIFIED by error<FirSourceElement, PsiElement> {
+            parameter<FirTypeParameterSymbol>("typeParameter")
+        }
     }
 
     val REFLECTION by object : DiagnosticGroup("Reflection") {

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -193,6 +193,7 @@ object FirErrors {
     val TYPE_PARAMETER_IN_CATCH_CLAUSE by error0<FirSourceElement, PsiElement>()
     val GENERIC_THROWABLE_SUBCLASS by error0<FirSourceElement, KtTypeParameterList>()
     val INNER_CLASS_OF_GENERIC_THROWABLE_SUBCLASS by error0<FirSourceElement, KtClassOrObject>(SourceElementPositioningStrategies.DECLARATION_NAME)
+    val TYPE_PARAMETER_AS_REIFIED by error1<FirSourceElement, PsiElement, FirTypeParameterSymbol>()
 
     // Reflection
     val CALLABLE_REFERENCE_LHS_NOT_A_CLASS by error0<FirSourceElement, KtExpression>()

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

@@ -53,6 +53,13 @@ object FirGetClassCallChecker : FirBasicExpressionChecker() {
             return
         }
 
+        argument.safeAsTypeParameterSymbol?.let {
+            if (!it.fir.isReified) {
+                // E.g., fun <T: Any> foo(): Any = T::class
+                reporter.reportOn(source, FirErrors.TYPE_PARAMETER_AS_REIFIED, it, context)
+            }
+        }
+
         if (argument !is FirResolvedQualifier) return
         // TODO: differentiate RESERVED_SYNTAX_IN_CALLABLE_REFERENCE_LHS
         if (argument.typeArguments.isNotEmpty() && !argument.typeRef.coneType.isAllowedInClassLiteral(context)) {
@@ -71,8 +78,14 @@ object FirGetClassCallChecker : FirBasicExpressionChecker() {
         get() {
             return this is FirResolvedQualifier ||
                     this is FirResolvedReifiedParameterReference ||
-                    ((this is FirQualifiedAccessExpression) &&
-                            (this.calleeReference as? FirResolvedNamedReference)?.resolvedSymbol is FirTypeParameterSymbol)
+                    safeAsTypeParameterSymbol != null
+        }
+
+    private val FirExpression.safeAsTypeParameterSymbol: FirTypeParameterSymbol?
+        get() {
+            return ((this as? FirQualifiedAccessExpression)
+                ?.calleeReference as? FirResolvedNamedReference)
+                ?.resolvedSymbol as? FirTypeParameterSymbol
         }
 
     private fun ConeKotlinType.isAllowedInClassLiteral(context: CheckerContext): Boolean =

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -185,6 +185,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_ARGUMENTS_NO
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_MISMATCH
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETERS_IN_ENUM
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETERS_IN_OBJECT
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETER_AS_REIFIED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETER_AS_SUPERTYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETER_IN_CATCH_CLAUSE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETER_IS_NOT_AN_EXPRESSION
@@ -394,6 +395,8 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(REIFIED_TYPE_IN_CATCH_CLAUSE, "Reified type is forbidden for catch parameter")
             map.put(TYPE_PARAMETER_IN_CATCH_CLAUSE, "Type parameter is forbidden for catch parameter")
 
+            map.put(TYPE_PARAMETER_AS_REIFIED, "Cannot use ''{0}'' as reified type parameter. Use a class instead", SYMBOL)
+
             // Reflection
             map.put(CALLABLE_REFERENCE_LHS_NOT_A_CLASS, "Left-hand side of a callable reference cannot be a type parameter")
 

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDiagnosticRenderers.kt

@@ -17,6 +17,7 @@ import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.render
 
@@ -27,6 +28,7 @@ object FirDiagnosticRenderers {
         when (symbol) {
             is FirClassLikeSymbol<*> -> symbol.classId.asString()
             is FirCallableSymbol<*> -> symbol.callableId.toString()
+            is FirTypeParameterSymbol -> symbol.name.asString()
             else -> "???"
         }
     }

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

@@ -9,7 +9,7 @@ val l1 = <!NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>List<String>?::class<!>
 val l2 = <!NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>List?::class<!>
 
 fun <T : Any> foo() {
-    val t1 = <!TYPE_PARAMETER_IS_NOT_AN_EXPRESSION!>T<!>::class
+    val t1 = <!TYPE_PARAMETER_AS_REIFIED!><!TYPE_PARAMETER_IS_NOT_AN_EXPRESSION!>T<!>::class<!>
     val t2 = <!NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!><!TYPE_PARAMETER_IS_NOT_AN_EXPRESSION!>T<!>?::class<!>
 }
 

compiler/testData/diagnostics/tests/generics/tpAsReified/ClassDereference.fir.kt

@@ -1,3 +1,3 @@
 
 fun <T: Any> dereferenceClass(): Any =
-        <!OTHER_ERROR!>T<!>::class
+        <!TYPE_PARAMETER_AS_REIFIED!><!TYPE_PARAMETER_IS_NOT_AN_EXPRESSION!>T<!>::class<!>

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -797,6 +797,13 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.TYPE_PARAMETER_AS_REIFIED) { firDiagnostic ->
+        TypeParameterAsReifiedImpl(
+            firSymbolBuilder.buildTypeParameterSymbol(firDiagnostic.a.fir as FirTypeParameter),
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.CALLABLE_REFERENCE_LHS_NOT_A_CLASS) { firDiagnostic ->
         CallableReferenceLhsNotAClassImpl(
             firDiagnostic as FirPsiDiagnostic<*>,

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -564,6 +564,11 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = InnerClassOfGenericThrowableSubclass::class
     }
 
+    abstract class TypeParameterAsReified : KtFirDiagnostic<PsiElement>() {
+        override val diagnosticClass get() = TypeParameterAsReified::class
+        abstract val typeParameter: KtTypeParameterSymbol
+    }
+
     abstract class CallableReferenceLhsNotAClass : KtFirDiagnostic<KtExpression>() {
         override val diagnosticClass get() = CallableReferenceLhsNotAClass::class
     }

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -913,6 +913,14 @@ internal class InnerClassOfGenericThrowableSubclassImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class TypeParameterAsReifiedImpl(
+    override val typeParameter: KtTypeParameterSymbol,
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.TypeParameterAsReified(), KtAbstractFirDiagnostic<PsiElement> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class CallableReferenceLhsNotAClassImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,