[FIR] Add NOT_A_CLASS diagnostics

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

@@ -914,6 +914,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.NOT_A_CLASS) { firDiagnostic ->
+        NotAClassImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.OPT_IN_USAGE) { firDiagnostic ->
         OptInUsageImpl(
             firDiagnostic.a,

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

@@ -659,6 +659,10 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = RepeatedAnnotationWarning::class
     }
 
+    abstract class NotAClass : KtFirDiagnostic<PsiElement>() {
+        override val diagnosticClass get() = NotAClass::class
+    }
+
     abstract class OptInUsage : KtFirDiagnostic<PsiElement>() {
         override val diagnosticClass get() = OptInUsage::class
         abstract val optInMarkerFqName: FqName

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

@@ -790,6 +790,11 @@ internal class RepeatedAnnotationWarningImpl(
     override val token: ValidityToken,
 ) : KtFirDiagnostic.RepeatedAnnotationWarning(), KtAbstractFirDiagnostic<KtAnnotationEntry>
 
+internal class NotAClassImpl(
+    override val firDiagnostic: KtPsiDiagnostic,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.NotAClass(), KtAbstractFirDiagnostic<PsiElement>
+
 internal class OptInUsageImpl(
     override val optInMarkerFqName: FqName,
     override val message: String,

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

@@ -281,6 +281,7 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
         val INAPPLICABLE_FILE_TARGET by error<KtAnnotationEntry>(PositioningStrategy.ANNOTATION_USE_SITE)
         val REPEATED_ANNOTATION by error<KtAnnotationEntry>()
         val REPEATED_ANNOTATION_WARNING by warning<KtAnnotationEntry>()
+        val NOT_A_CLASS by error<PsiElement>()
     }
 
     val OPT_IN by object : DiagnosticGroup("OptIn") {

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

@@ -247,6 +247,7 @@ object FirErrors {
     val INAPPLICABLE_FILE_TARGET by error0<KtAnnotationEntry>(SourceElementPositioningStrategies.ANNOTATION_USE_SITE)
     val REPEATED_ANNOTATION by error0<KtAnnotationEntry>()
     val REPEATED_ANNOTATION_WARNING by warning0<KtAnnotationEntry>()
+    val NOT_A_CLASS by error0<PsiElement>()
 
     // OptIn
     val OPT_IN_USAGE by warning2<PsiElement, FqName, String>(SourceElementPositioningStrategies.REFERENCE_BY_QUALIFIED)

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

@@ -13,7 +13,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.syntax.FirUnderscoredTypeArgum
 object CommonExpressionCheckers : ExpressionCheckers() {
     override val annotationCallCheckers: Set<FirAnnotationCallChecker>
         get() = setOf(
-            FirAnnotationArgumentChecker,
+            FirAnnotationExpressionChecker,
             FirOptInAnnotationCallChecker,
         )
 

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

@@ -7,23 +7,27 @@ package org.jetbrains.kotlin.fir.analysis.checkers.expression
 
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.config.ApiVersion
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.KtDiagnosticFactory0
+import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.ConstantArgumentKind
 import org.jetbrains.kotlin.fir.analysis.checkers.checkConstantArguments
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
-import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
-import org.jetbrains.kotlin.diagnostics.KtDiagnosticFactory0
-import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.declarations.findArgumentByName
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.languageVersionSettings
+import org.jetbrains.kotlin.fir.references.FirErrorNamedReference
 import org.jetbrains.kotlin.fir.resolve.fqName
+import org.jetbrains.kotlin.fir.types.ConeClassLikeType
+import org.jetbrains.kotlin.fir.types.FirErrorTypeRef
+import org.jetbrains.kotlin.fir.types.coneType
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.RequireKotlinConstants
 
-object FirAnnotationArgumentChecker : FirAnnotationCallChecker() {
+object FirAnnotationExpressionChecker : FirAnnotationCallChecker() {
     private val versionArgumentName = Name.identifier("version")
     private val deprecatedSinceKotlinFqName = FqName("kotlin.DeprecatedSinceKotlin")
     private val sinceKotlinFqName = FqName("kotlin.SinceKotlin")
@@ -44,13 +48,8 @@ object FirAnnotationArgumentChecker : FirAnnotationCallChecker() {
 
         checkAnnotationsWithVersion(fqName, expression, context, reporter)
         checkDeprecatedSinceKotlin(expression.source, fqName, argumentMapping, context, reporter)
-
+        checkAnnotationUsedAsAnnotationArgument(expression, context, reporter)
-        val args = expression.argumentList.arguments
+        checkNotAClass(expression, context, reporter)
-        for (arg in args) {
-            for (ann in arg.unwrapArgument().annotations) {
-                reporter.reportOn(ann.source, FirErrors.ANNOTATION_USED_AS_ANNOTATION_ARGUMENT, context)
-            }
-        }
     }
 
     private fun checkAnnotationArgumentWithSubElements(
@@ -194,4 +193,31 @@ object FirAnnotationArgumentChecker : FirAnnotationCallChecker() {
             reporter.reportOn(source, FirErrors.DEPRECATED_SINCE_KOTLIN_WITH_UNORDERED_VERSIONS, context)
         }
     }
+
+    private fun checkAnnotationUsedAsAnnotationArgument(
+        expression: FirAnnotationCall,
+        context: CheckerContext,
+        reporter: DiagnosticReporter
+    ) {
+        val args = expression.argumentList.arguments
+        for (arg in args) {
+            for (ann in arg.unwrapArgument().annotations) {
+                reporter.reportOn(ann.source, FirErrors.ANNOTATION_USED_AS_ANNOTATION_ARGUMENT, context)
+            }
+        }
+    }
+
+    private fun checkNotAClass(
+        expression: FirAnnotationCall,
+        context: CheckerContext,
+        reporter: DiagnosticReporter
+    ) {
+        val annotationTypeRef = expression.annotationTypeRef
+        if (expression.calleeReference is FirErrorNamedReference &&
+            annotationTypeRef !is FirErrorTypeRef &&
+            annotationTypeRef.coneType !is ConeClassLikeType
+        ) {
+            reporter.reportOn(annotationTypeRef.source, FirErrors.NOT_A_CLASS, context)
+        }
+    }
 }

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

@@ -306,6 +306,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_VARARG_SPREAD
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOTHING_TO_INLINE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOTHING_TO_OVERRIDE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_AN_ANNOTATION_CLASS
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_A_CLASS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_A_FUNCTION_LABEL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_A_LOOP_LABEL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_A_SUPERTYPE
@@ -779,6 +780,7 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
             OPT_IN_MARKER_ON_OVERRIDE_WARNING,
             "Opt-in requirement marker annotation on override makes no sense without the same marker on base declaration"
         )
+        map.put(NOT_A_CLASS, "Not a class")
 
         // Exposed visibility group // #
         map.put(

compiler/testData/diagnostics/tests/annotations/typeParameterAsAnnotation.fir.kt

@@ -1,9 +0,0 @@
-class Foo<T> {
-    @T
-    fun foo() = 0
-}
-
-class Bar<T : Annotation> {
-    @T
-    fun foo() = 0
-}

compiler/testData/diagnostics/tests/annotations/typeParameterAsAnnotation.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 class Foo<T> {
     @<!NOT_A_CLASS!>T<!>
     fun foo() = 0