Disallow usages of experimental markers as qualifiers

Only allow explicit imports of markers, but not of nested classes
declared in them

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExperimentalUsageChecker.kt

@@ -26,7 +26,6 @@ import org.jetbrains.kotlin.incremental.components.NoLookupLocation
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.*
-import org.jetbrains.kotlin.psi.psiUtil.getParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.getTopmostParentQualifiedExpressionForSelector
 import org.jetbrains.kotlin.resolve.*
 import org.jetbrains.kotlin.resolve.calls.checkers.CallChecker
@@ -246,7 +245,7 @@ class ExperimentalUsageChecker(project: Project) : CallChecker {
                 else -> null
             }
             if (targetClass != null && targetClass.loadExperimentalityForMarkerAnnotation() != null) {
-                if (!element.isUsageAsAnnotationOrQualifier() &&
+                if (!element.isUsageAsAnnotationOrImport() &&
                     !element.isUsageAsUseExperimentalArgument(context.trace.bindingContext)
                 ) {
                     context.trace.report(
@@ -261,12 +260,12 @@ class ExperimentalUsageChecker(project: Project) : CallChecker {
                 context.trace.report(Errors.EXPERIMENTAL_IS_NOT_ENABLED.on(element))
             }
 
-            if (!element.isUsageAsAnnotationOrQualifier()) {
+            if (!element.isUsageAsAnnotationOrImport() && !element.isUsageAsQualifier()) {
                 context.trace.report(Errors.EXPERIMENTAL_CAN_ONLY_BE_USED_AS_ANNOTATION.on(element))
             }
         }
 
-        private fun PsiElement.isUsageAsAnnotationOrQualifier(): Boolean {
+        private fun PsiElement.isUsageAsAnnotationOrImport(): Boolean {
             val parent = parent
 
             if (parent is KtUserType) {
@@ -275,6 +274,10 @@ class ExperimentalUsageChecker(project: Project) : CallChecker {
                         parent.parent.parent.parent is KtAnnotationEntry
             }
 
+            return parent is KtDotQualifiedExpression && parent.parent is KtImportDirective
+        }
+
+        private fun PsiElement.isUsageAsQualifier(): Boolean {
             if (this is KtSimpleNameExpression) {
                 val qualifier = getTopmostParentQualifiedExpressionForSelector() ?: this
                 if ((qualifier.parent as? KtDotQualifiedExpression)?.receiverExpression == qualifier) {
@@ -282,8 +285,6 @@ class ExperimentalUsageChecker(project: Project) : CallChecker {
                 }
             }
 
-            if (getParentOfType<KtImportDirective>(true) != null) return true
-
             return false
         }
 

compiler/testData/diagnostics/testsWithStdLib/experimental/usageNotAsAnnotation.kt

@@ -1,5 +1,7 @@
+// !LANGUAGE: +NestedClassesInAnnotations
 // !USE_EXPERIMENTAL: kotlin.Experimental
 // !DIAGNOSTICS: -UNUSED_PARAMETER
+// FILE: api.kt
 
 package test
 
@@ -43,7 +45,13 @@ fun f5() {}
 // Usages of markers as types should be errors
 
 @Experimental
-annotation class Marker
+annotation class Marker {
+    class NestedClass
+
+    companion object {
+        const val value = 42
+    }
+}
 
 fun f6(m: <!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>) {}
 fun f7(): List<<!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>>? = null
@@ -52,3 +60,18 @@ fun f8(): test.<!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_
 typealias Marker0 = <!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>
 
 fun f9(m: <!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker0<!>) {}
+
+
+// Usages of markers as qualifiers are errors as well (we can lift this restriction for select cases)
+
+fun f10(m: <!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>.NestedClass) {
+    <!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>.value
+}
+
+// FILE: usage-from-other-file.kt
+
+// Usages of markers in import statements should be OK, but not as qualifiers to import their nested classes
+
+import test.Marker
+import test.<!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>.NestedClass
+import test.<!EXPERIMENTAL_MARKER_CAN_ONLY_BE_USED_AS_ANNOTATION_OR_ARGUMENT_IN_USE_EXPERIMENTAL!>Marker<!>.Companion

compiler/testData/diagnostics/testsWithStdLib/experimental/usageNotAsAnnotation.txt

@@ -2,6 +2,7 @@ package
 
 package test {
     public fun f1(/*0*/ e: kotlin.Experimental): kotlin.Unit
+    public fun f10(/*0*/ m: test.Marker.NestedClass): kotlin.Unit
     public fun f2(/*0*/ u: kotlin.UseExperimental?): kotlin.Unit
     public fun f3(/*0*/ e: test.Experimental0 /* = kotlin.Experimental */): kotlin.Unit
     public fun f4(/*0*/ u: test.UseExperimental0 /* = kotlin.UseExperimental */): kotlin.Unit
@@ -23,6 +24,21 @@ package test {
         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
+
+        public companion object Companion {
+            private constructor Companion()
+            public const final val value: kotlin.Int = 42
+            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
+        }
+
+        public final class NestedClass {
+            public constructor NestedClass()
+            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
+        }
     }
 
     public final annotation class VarargKClasses : kotlin.Annotation {