Ensure that the pubspecs of both _macros and macros packages are updated whenever the lib/ dir of _macros is edited.

Related to https://dart-review.googlesource.com/c/sdk/+/359040

Change-Id: Iab3cfa89e0492282c348c6a72f3032191fa4998f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/359580
Auto-Submit: Jake Macdonald <jakemac@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>

pkg/_macros/PRESUBMIT.py

diff --git a/pkg/_macros/PRESUBMIT.py b/pkg/_macros/PRESUBMIT.py
new file mode 100644
index 0000000..d7482f3
--- /dev/null
+++ b/pkg/_macros/PRESUBMIT.py
@@ -0,0 +1,52 @@
+#!/usr/bin/env python3
+# Copyright (c) 2024, 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.
+"""_macros package presubmit python script.
+
+See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
+for more details about the presubmit API built into gcl.
+"""
+
+PRESUBMIT_VERSION = '2.0.0'
+USE_PYTHON3 = True
+
+
+# Ensures that the pubspec of `package_name` has been altered.
+#
+# Returns a list of errors if not.
+#
+# TODO(jakemac): Ensure the version was bumped as well.
+def EnsurePubspecAltered(input_api, package_name):
+    errors = []
+    package_path = 'pkg/%s' % package_name
+    pubspec_path = '%s/pubspec.yaml' % package_path
+    pubspec_changed = any(file.LocalPath() == pubspec_path
+                          for file in input_api.change.AffectedFiles())
+    if not pubspec_changed:
+        errors.append(
+            ('The pkg/_macros/lib dir was altered but the version of %s was '
+             'not bumped. See pkg/_macros/CONTRIBUTING.md' % package_path))
+    return errors
+
+
+# Invoked on upload and commit.
+def CheckChange(input_api, output_api):
+    errors = []
+
+    # If the `lib` dir is altered, we also require a change to the pubspec.yaml
+    # of both this package and the `macros` package.
+    lib_changed = any(file.LocalPath().startswith('pkg/_macros/lib')
+                      for file in input_api.AffectedFiles())
+    if lib_changed:
+        errors += EnsurePubspecAltered(input_api, '_macros')
+        errors += EnsurePubspecAltered(input_api, 'macros')
+
+    if errors:
+        return [
+            output_api.PresubmitError(
+                'pkg/_macros presubmit/PRESUBMIT.py failure(s):',
+                long_text='\n\n'.join(errors))
+        ]
+
+    return []