Add a new hook to forbid new submodules

pre_commit_hooks/forbid_new_submodules.py

@@ -0,0 +1,31 @@
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+from pre_commit_hooks.util import cmd_output
+
+
+def main(argv=None):
+    # `argv` is ignored, pre-commit will send us a list of files that we
+    # don't care about
+    added_diff = cmd_output(
+        'git', 'diff', '--staged', '--diff-filter=A', '--raw',
+    )
+    retv = 0
+    for line in added_diff.splitlines():
+        metadata, filename = line.split('\t', 1)
+        new_mode = metadata.split(' ')[1]
+        if new_mode == '160000':
+            print('{}: new submodule introduced'.format(filename))
+            retv = 1
+
+    if retv:
+        print('This commit introduces new submodules.')
+        print('Did you unintentionally `git add .`?')
+        print('To fix: git rm {thesubmodule}  # no trailing slash')
+        print('Also check .gitmodules')
+
+    return retv
+
+
+if __name__ == '__main__':
+    exit(main())