add a hook to autoupdate black in user configuration

.pre-commit-hooks.yaml

@@ -6,3 +6,12 @@
   require_serial: true
   types: [file]
   files: \.(py|rst)$
+
+- id: blackdoc-autoupdate-black
+  name: autoupdate-black
+  entry: python -m blackdoc.autoupdate
+  language: python
+  language_version: python3
+  require_serial: true
+  types: [file]
+  files: \.pre-commit-config\.yaml

blackdoc/autoupdate.py

@@ -0,0 +1,33 @@
+import argparse
+import re
+
+version_re = re.compile(r"black\s+rev: (.+)\s+hooks:\s+- id: black")
+black_pin_re = re.compile(
+    r"(- id: blackdoc.+?additional_dependencies:.+?black==)[.\w]+",
+    re.DOTALL,
+)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("path")
+    args = parser.parse_args()
+    with open(args.path) as f:
+        content = f.read()
+
+    match = version_re.search(content)
+    if match is None:
+        raise ValueError("cannot find the black hook")
+    version = match.group(1)
+    replaced = black_pin_re.sub(rf"\g<1>{version}", content)
+
+    if content != replaced:
+        with open(args.path, mode="w") as f:
+            f.write(replaced)
+        return 1
+    else:
+        return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

doc/changelog.rst

@@ -4,6 +4,8 @@ v0.4.0 (*unreleased*)
 ---------------------
 - replace docstrings by modifying by token (:pull:`144`)
 - switch the html theme to `furo <https://pradyunsg.me/furo>`_ (:pull:`149`)
+- add a new hook to synchronize `black` pinned in `additional_dependencies` with the version from
+  the `black` hook (:pull:`124`)
 
 v0.3.6 (25 August 2022)
 -----------------------