meta: Introduce TargetKind.directive

Fixes https://github.com/dart-lang/sdk/issues/52274

Change-Id: I67884caf86502d4edd848eb32a30097488e09db9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/360480
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

pkg/meta/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 - Introduce `TargetKind.constructor`, to indicate that an annotation is valid on
   any constructor.
+- Introduce `TargetKind.directive`, to indicate that an annotation is valid on
+  any directive.
 - Introduce `TargetKind.typeParamteer`, to indicate that an annotation is valid
   on any type parameter.
 - Introduce `@doNotSubmit` to annotate members that should not be submitted to

pkg/meta/lib/meta_meta.dart

@@ -48,6 +48,11 @@ class TargetKind {
   /// because there is no way to annotate a primary constructor.
   static const constructor = TargetKind._('constructors', 'constructor');
 
+  /// Indicates that an annotation is valid on any directive in a library or
+  /// part file, whether it's a `library`, `import`, `export`, `part`, or
+  /// `part of` directive.
+  static const directive = TargetKind._('directives', 'directive');
+
   /// Indicates that an annotation is valid on any enum declaration.
   static const enumType = TargetKind._('enums', 'enumType');
 
@@ -119,6 +124,7 @@ class TargetKind {
   static const values = [
     classType,
     constructor,
+    directive,
     enumType,
     extension,
     extensionType,