opt working/macros/example/bin/run.dart into null safety

Author: jakemac53

working/macros/example/README.md

@@ -6,14 +6,9 @@ actually running those examples.
 
 ## Setup
 
-You may need to edit the `pubspec.yaml` file to run these examples. It requires
-a path dependency on the SDK packages to work (until
-https://github.com/dart-lang/pub/issues/3336 is resolved). The current paths
-assume the dart sdk is in a sibling directory to the language repo, in a
-directory called `dart-lang-sdk`.
-
-Your SDK will also need to be very recent, in particular it must include
-commit 54e773.
+Your SDK will need to match roughly the commit pinned in the pubspec.yaml file
+of this package (see the `ref` lines). Otherwise you will get a kernel version
+mismatch.
 
 ## Benchmarks
 

working/macros/example/bin/run.dart

@@ -1,8 +1,6 @@
 // Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-//
-// @dart=2.9
 
 import 'dart:io';
 import 'dart:isolate';
@@ -46,7 +44,7 @@ void main() async {
       File(bootstrapFile.uri.resolve('bootstrap.dart.dill').toFilePath());
 
   var feAnalyzerSharedRoot = (await Isolate.resolvePackageUri(
-          Uri.parse('package:_fe_analyzer_shared/fake.dart')))
+          Uri.parse('package:_fe_analyzer_shared/fake.dart')))!
       .resolve('./');
 
   log('Compiling macro program to kernel (${bootstrapKernelFile.path})');
@@ -90,7 +88,7 @@ void main() async {
     '--output',
     output.path,
     '--source',
-    Platform.script.resolve('user_main.dart').toFilePath(),
+    Uri.base.resolve('bin/user_main.dart').toFilePath(),
     '--packages-file=.dart_tool/package_config.json',
     '--enable-experiment=macros',
     '--precompiled-macro-format=kernel',