Class is an annotation iff it is annotated by kotlin.annotation.annotation, or is kotlin.annotation.annotation itself.

JetClassOrObject.isAnnotation() is no more in use during resolve. Additional test.

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

@@ -0,0 +1,25 @@
+// FILE: a.kt
+
+<!NOT_AN_ANNOTATION_CLASS!>annotation<!> class annotation
+
+// FILE: test/b.kt
+
+package test
+
+<!NOT_AN_ANNOTATION_CLASS!>test.annotation<!> class annotation
+
+kotlin.annotation.annotation class realAnnotation
+
+realAnnotation class My
+
+// FILE: other/c.kt
+
+package other
+
+annotation class My
+
+<!NOT_AN_ANNOTATION_CLASS!>test.annotation<!> class Your
+
+kotlin.annotation.annotation class His
+
+My class Our

compiler/testData/diagnostics/tests/annotations/AnnotationIdentifier.txt

@@ -0,0 +1,63 @@
+package
+
+annotation() internal final class annotation {
+    public constructor annotation()
+    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
+}
+
+package other {
+
+    kotlin.annotation.annotation() internal final class His : kotlin.Annotation {
+        public constructor His()
+        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
+    }
+
+    kotlin.annotation.annotation() internal final class My : kotlin.Annotation {
+        public constructor My()
+        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
+    }
+
+    other.My() internal final class Our {
+        public constructor Our()
+        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
+    }
+
+    test.annotation() internal final class Your {
+        public constructor Your()
+        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
+    }
+}
+
+package test {
+
+    test.realAnnotation() internal final class My {
+        public constructor My()
+        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
+    }
+
+    test.annotation() internal final class annotation {
+        public constructor annotation()
+        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
+    }
+
+    kotlin.annotation.annotation() internal final class realAnnotation : kotlin.Annotation {
+        public constructor realAnnotation()
+        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
+    }
+}

compiler/testData/diagnostics/tests/annotations/options/annotation.kt

@@ -4,14 +4,13 @@ enum class Target {
     FUNCTION
 }
 
-target(Target.CLASSIFIER)
-public annotation class target(vararg val allowedTargets: Target)
+<!NOT_AN_ANNOTATION_CLASS!>target(Target.CLASSIFIER)<!>
+public <!NOT_AN_ANNOTATION_CLASS!>annotation<!> class target(vararg val allowedTargets: Target)
 
-target(Target.CLASSIFIER)
-public annotation(AnnotationRetention.SOURCE) class annotation(
+<!NOT_AN_ANNOTATION_CLASS!>target(Target.CLASSIFIER)<!>
+public <!NOT_AN_ANNOTATION_CLASS!>annotation(AnnotationRetention.SOURCE)<!> class annotation(
     val retention: AnnotationRetention = AnnotationRetention.RUNTIME,
     val repeatable: Boolean = false
 )
 
-annotation class some
-
+<!NOT_AN_ANNOTATION_CLASS!>annotation<!> class some

compiler/testData/diagnostics/tests/annotations/options/annotation.txt

@@ -34,7 +34,7 @@ internal final enum class Target : kotlin.Enum<Target> {
     public final /*synthesized*/ fun values(): kotlin.Array<Target>
 }
 
-target(allowedTargets = {Target.CLASSIFIER}) annotation(retention = AnnotationRetention.SOURCE) public final class annotation : kotlin.Annotation {
+target(allowedTargets = {Target.CLASSIFIER}) annotation(retention = AnnotationRetention.SOURCE) public final class annotation {
     public constructor annotation(/*0*/ retention: kotlin.annotation.AnnotationRetention = ..., /*1*/ repeatable: kotlin.Boolean = ...)
     internal final val repeatable: kotlin.Boolean
     internal final val retention: kotlin.annotation.AnnotationRetention
@@ -43,14 +43,14 @@ target(allowedTargets = {Target.CLASSIFIER}) annotation(retention = AnnotationRe
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-annotation() internal final class some : kotlin.Annotation {
+annotation() internal final class some {
     public constructor some()
     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
 }
 
-target(allowedTargets = {Target.CLASSIFIER}) annotation() public final class target : kotlin.Annotation {
+target(allowedTargets = {Target.CLASSIFIER}) annotation() public final class target {
     public constructor target(/*0*/ vararg allowedTargets: Target /*kotlin.Array<out Target>*/)
     internal final val allowedTargets: kotlin.Array<out Target>
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean