Mention directive annotations in CHANGELOG and example. (#772)

Author: davidmorgan

example/lib/src/multiplier_generator.dart

@@ -19,4 +19,15 @@ class MultiplierGenerator extends GeneratorForAnnotation<Multiplier> {
 
     return 'num ${element.name3}Multiplied() => ${element.name3} * $numValue;';
   }
+
+  // Override this method to respond to annotations on directives: `import`,
+  // `export`, `library` and/or `part`.
+  //
+  // This generator doesn't respond to such annotations, so do nothing.
+  @override
+  dynamic generateForAnnotatedDirective(
+    ElementDirective directive,
+    ConstantReader annotation,
+    BuildStep buildStep,
+  );
 }

source_gen/CHANGELOG.md

@@ -4,6 +4,10 @@
   do resolution need to switch to the new API, see
   https://github.com/dart-lang/sdk/blob/main/pkg/analyzer/doc/element_model_migration_guide.md.
   For questions please use https://github.com/dart-lang/build/discussions.
+- **Breaking Change**: annotations are now reported separately for elements
+  and directives. If you use `TypeChecker().annotatedWith()`, see also
+  the new `TypeChecker().libraryDirectivesAnnotatedWith()`. If you use
+  `GeneratorForAnnotation` see the new `generateForAnnotatedDirective`.
 - Require `build: ^3.0.0`
 - Updated the minimum package versions for a number of dependencies.
 - Require Dart 3.7.0