Add a post-sync hook to generate the package_config.json file.

Change-Id: I19967e8ae7eaa4e3071e335e43932e27128d8173
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/235764
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Devon Carew <devoncarew@google.com>

DEPS

@@ -697,6 +697,12 @@ deps_os = {
 }
 
 hooks = [
+  {
+    # Generate the .dart_tool/package_confg.json file.
+    'name': 'Generate .dart_tool/package_confg.json',
+    'pattern': '.',
+    'action': ['python3', 'sdk/tools/generate_package_config.py'],
+  },
   {
     # Pull Debian sysroot for i386 Linux
     'name': 'sysroot_i386',

tools/generate_package_config.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+# 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.
+
+# Invoke the `tools/generate_package_config.dart` script.
+
+import os
+import os.path
+import platform
+import subprocess
+import sys
+
+USE_PYTHON3 = True
+
+
+def is_windows():
+    os_id = platform.system()
+    return os_id == 'Windows'
+
+
+def checked_in_sdk_path():
+    tools_dir = os.path.dirname(os.path.realpath(__file__))
+    return os.path.join(tools_dir, 'sdks', 'dart-sdk')
+
+
+def checked_in_sdk_executable():
+    name = 'dart'
+    if is_windows():
+        name = 'dart.exe'
+    return os.path.join(checked_in_sdk_path(), 'bin', name)
+
+
+def generate_package_config():
+    tools_dir = os.path.dirname(os.path.realpath(__file__))
+    process = subprocess.run([
+        checked_in_sdk_executable(),
+        os.path.join(tools_dir, 'generate_package_config.dart')
+    ])
+    return process.returncode
+
+
+def Main():
+    sys.exit(generate_package_config())
+
+
+if __name__ == '__main__':
+    Main()