validate _sync directory during lint phase

noxfile.py

@@ -66,9 +66,10 @@ def format(session):
 
 @nox.session(python="3.12")
 def lint(session):
-    session.install("flake8", "black~=24.0", "isort")
+    session.install("flake8", "black~=24.0", "isort", "unasync", "setuptools")
     session.run("black", "--check", "--target-version=py37", *SOURCE_FILES)
     session.run("isort", "--check", *SOURCE_FILES)
+    session.run("python", "utils/run-unasync.py", "check")
     session.run("flake8", "--ignore=E501,E741,W503", *SOURCE_FILES)
     session.run("python", "utils/license-headers.py", "check", *SOURCE_FILES)
 

utils/run-unasync.py

@@ -16,12 +16,16 @@
 #  under the License.
 
 import os
+import subprocess
+import sys
 from pathlib import Path
 
 import unasync
 
 
-def main():
+def main(check=False):
+    output_dir = "_sync" if not check else "_sync_check"
+
     # Unasync all the generated async code
     additional_replacements = {
         "aiter": "iter",
@@ -35,7 +39,7 @@ def main():
     rules = [
         unasync.Rule(
             fromdir="/elasticsearch_dsl/_async/",
-            todir="/elasticsearch_dsl/_sync/",
+            todir=f"/elasticsearch_dsl/{output_dir}/",
             additional_replacements=additional_replacements,
         ),
     ]
@@ -53,6 +57,22 @@ def main():
 
     unasync.unasync_files(filepaths, rules)
 
+    if check:
+        # make sure there are no differences between _sync and _sync_check
+        subprocess.check_call(
+            ["black", "--target-version=py37", "elasticsearch_dsl/_sync_check/"]
+        )
+        subprocess.check_call(
+            [
+                "diff",
+                "-x",
+                "__pycache__",
+                "elasticsearch_dsl/_sync",
+                "elasticsearch_dsl/_sync_check",
+            ]
+        )
+        subprocess.check_call(["rm", "-rf", "elasticsearch_dsl/_sync_check"])
+
 
 if __name__ == "__main__":
-    main()
+    main(check="check" in sys.argv)