Add --watch to _macro_tool for analyzer.

pkgs/_macro_tool/bin/main.dart

@@ -14,7 +14,9 @@ final argParser = ArgParser()
   ..addOption('workspace', help: 'Path to workspace.')
   ..addOption('packageConfig', help: 'Path to package config.')
   ..addOption('script', help: 'Path to script.')
-  ..addFlag('skip-cleanup');
+  ..addFlag('skip-cleanup',
+      help: 'Whether to skip delete of augmentations and revert of script.')
+  ..addFlag('watch', help: 'Whether to watch for changes.');
 
 Future<void> main(List<String> arguments) async {
   final args = argParser.parse(arguments);
@@ -40,6 +42,7 @@ ${argParser.usage}''');
       workspacePath: p.canonicalize(workspace),
       packageConfigPath: p.canonicalize(packageConfig),
       scriptPath: p.canonicalize(script),
-      skipCleanup: args['skip-cleanup'] as bool);
+      skipCleanup: args['skip-cleanup'] as bool,
+      watch: args['watch'] as bool);
   await tool.run();
 }

pkgs/_macro_tool/lib/analyzer_macro_tool.dart

@@ -7,6 +7,7 @@ import 'dart:io';
 import 'package:_analyzer_macros/macro_implementation.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/results.dart';
+import 'package:analyzer/diagnostic/diagnostic.dart';
 import 'package:analyzer/src/summary2/macro_injected_impl.dart'
     as injected_analyzer;
 import 'package:macro_service/macro_service.dart';
@@ -18,7 +19,8 @@ class AnalyzerMacroTool extends MacroTool {
       {required super.workspacePath,
       required super.packageConfigPath,
       required super.scriptPath,
-      required super.skipCleanup})
+      required super.skipCleanup,
+      required super.watch})
       : super.internal();
 
   /// Runs macros in [scriptFile] on the analyzer.
@@ -38,30 +40,47 @@ class AnalyzerMacroTool extends MacroTool {
                 version: ProtocolVersion.macros1),
             packageConfig: Uri.file(packageConfigPath));
 
-    final resolvedLibrary = (await analysisContext.currentSession
-        .getResolvedLibrary(scriptPath)) as ResolvedLibraryResult;
+    ResolvedLibraryResult resolvedLibrary;
+    // `asBroadcastStream` so repeated use of `first` below waits for the next
+    // change.
+    var events = File(scriptPath).watch().asBroadcastStream();
+    var stopwatch = Stopwatch()..start();
+    while (true) {
+      resolvedLibrary = (await analysisContext.currentSession
+          .getResolvedLibrary(scriptPath)) as ResolvedLibraryResult;
+      print('Resolved in ${stopwatch.elapsedMilliseconds}ms.');
 
-    final errors = (await analysisContext.currentSession.getErrors(scriptPath))
-        as ErrorsResult;
-    if (errors.errors.isNotEmpty) {
-      print('Errors: ${errors.errors}');
-    }
+      final errors = (await analysisContext.currentSession
+          .getErrors(scriptPath)) as ErrorsResult;
+      final actualErrors =
+          errors.errors.where((e) => e.severity == Severity.error).toList();
+      if (actualErrors.isNotEmpty) {
+        print('Errors: $actualErrors');
+      }
 
-    final augmentationUnits =
-        resolvedLibrary.units.where((u) => u.isMacroPart).toList();
-    if (augmentationUnits.isEmpty) {
-      return false;
-    }
+      final augmentationUnits =
+          resolvedLibrary.units.where((u) => u.isMacroPart).toList();
+      if (augmentationUnits.isEmpty) {
+        return false;
+      }
 
-    print('Macro output (patched to use augment library): '
-        '$augmentationFilePath');
-    File(augmentationFilePath).writeAsStringSync(augmentationUnits
-        .single.content
-        // The analyzer produces augmentations in parts, but the CFE still
-        // wants them in augmentation libraries. Adjust the output accordingly.
-        .replaceAll('part of', 'augment library'));
+      print('Macro output (patched to use augment library): '
+          '$augmentationFilePath');
+      File(augmentationFilePath).writeAsStringSync(augmentationUnits
+          .single.content
+          // The analyzer produces augmentations in parts, but the CFE still
+          // wants them in augmentation libraries. Adjust the output accordingly.
+          .replaceAll('part of', 'augment library'));
 
-    return true;
+      if (!watch) return true;
+
+      print('Running with --watch, waiting for next change to script.');
+      await events.first;
+      print('Script changed, rerunning macro.');
+      stopwatch.reset();
+      analysisContext.changeFile(scriptPath);
+      await analysisContext.applyPendingFileChanges();
+    }
   }
 
   @override

pkgs/_macro_tool/lib/cfe_macro_tool.dart

@@ -17,7 +17,8 @@ class CfeMacroTool extends MacroTool {
       {required super.workspacePath,
       required super.packageConfigPath,
       required super.scriptPath,
-      required super.skipCleanup})
+      required super.skipCleanup,
+      required super.watch})
       : super.internal();
 
   /// Runs macros in [scriptFile] using the CFE.
@@ -27,6 +28,8 @@ class CfeMacroTool extends MacroTool {
   /// Returns whether an augmentation file was written.
   @override
   Future<bool> augment() async {
+    if (watch) throw UnimplementedError('--watch not implemented for CFE.');
+
     // TODO(davidmorgan): this dill comes from the Dart SDK running the test,
     // but `package:frontend_server` and `package:front_end` are used as a
     // library, so we will see version skew breakage. Find a better way.

pkgs/_macro_tool/lib/macro_tool.dart

@@ -15,30 +15,35 @@ abstract class MacroTool {
   String packageConfigPath;
   String scriptPath;
   bool skipCleanup;
+  bool watch;
 
   MacroTool.internal(
       {required this.workspacePath,
       required this.packageConfigPath,
       required this.scriptPath,
-      required this.skipCleanup});
+      required this.skipCleanup,
+      required this.watch});
 
   factory MacroTool(
           {required HostOption host,
           required String workspacePath,
           required String packageConfigPath,
           required String scriptPath,
-          required bool skipCleanup}) =>
+          required bool skipCleanup,
+          required bool watch}) =>
       host == HostOption.analyzer
           ? AnalyzerMacroTool(
               workspacePath: workspacePath,
               packageConfigPath: packageConfigPath,
               scriptPath: scriptPath,
-              skipCleanup: skipCleanup)
+              skipCleanup: skipCleanup,
+              watch: watch)
           : CfeMacroTool(
               workspacePath: workspacePath,
               packageConfigPath: packageConfigPath,
               scriptPath: scriptPath,
-              skipCleanup: skipCleanup);
+              skipCleanup: skipCleanup,
+              watch: watch);
 
   Future<void> run() async {
     print('Running ${p.basename(scriptPath)} with macros on $this.');