docs: add tools/docs/gen-renames.py

Add a new script that wraps git to trawl the repository history for
renames of .rst files in the Documentation/ directory.

Example usage:

  tools/docs/gen-renames.py --rev v6.17-rc3 > Documentation/.renames.txt

The output format is simply:

  <old path> SPACE <new path> NEWLINE

where neither <old path> nor <new path> contain the Documentation/
prefix or the .rst suffix. The file is sorted alphabetically.

We can suggest rerunning the script for future renames (and squash the
resulting change) or rerun it periodically to keep the file up to date.

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20250905144608.577449-2-vegard.nossum@oracle.com>

tools/docs/gen-renames.py

@@ -0,0 +1,130 @@
+#! /usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright © 2025, Oracle and/or its affiliates.
+# Author: Vegard Nossum <vegard.nossum@oracle.com>
+
+"""Trawl repository history for renames of Documentation/**.rst files.
+
+Example:
+
+    tools/docs/gen-renames.py --rev HEAD > Documentation/.renames.txt
+"""
+
+import argparse
+import itertools
+import os
+import subprocess
+import sys
+
+parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+parser.add_argument('--rev', default='HEAD', help='generate renames up to this revision')
+
+args = parser.parse_args()
+
+def normalize(path):
+    prefix = 'Documentation/'
+    suffix = '.rst'
+
+    assert path.startswith(prefix)
+    assert path.endswith(suffix)
+
+    return path[len(prefix):-len(suffix)]
+
+class Name(object):
+    def __init__(self, name):
+        self.names = [name]
+
+    def rename(self, new_name):
+        self.names.append(new_name)
+
+names = {
+}
+
+for line in subprocess.check_output([
+    'git', 'log',
+    '--reverse',
+    '--oneline',
+    '--find-renames',
+    '--diff-filter=RD',
+    '--name-status',
+    '--format=commit %H',
+    # ~v4.8-ish is when Sphinx/.rst was added in the first place
+    f'v4.8..{args.rev}',
+    '--',
+    'Documentation/'
+], text=True).splitlines():
+    # rename
+    if line.startswith('R'):
+        _, old, new = line[1:].split('\t', 2)
+
+        if old.endswith('.rst') and new.endswith('.rst'):
+            old = normalize(old)
+            new = normalize(new)
+
+            name = names.get(old)
+            if name is None:
+                name = Name(old)
+            else:
+                del names[old]
+
+            name.rename(new)
+            names[new] = name
+
+        continue
+
+    # delete
+    if line.startswith('D'):
+        _, old = line.split('\t', 1)
+
+        if old.endswith('.rst'):
+            old = normalize(old)
+
+            # TODO: we could save added/modified files as well and propose
+            # them as alternatives
+            name = names.get(old)
+            if name is None:
+                pass
+            else:
+                del names[old]
+
+        continue
+
+#
+# Get the set of current files so we can sanity check that we aren't
+# redirecting any of those
+#
+
+current_files = set()
+for line in subprocess.check_output([
+    'git', 'ls-tree',
+    '-r',
+    '--name-only',
+    args.rev,
+    'Documentation/',
+], text=True).splitlines():
+    if line.endswith('.rst'):
+        current_files.add(normalize(line))
+
+#
+# Format/group/output result
+#
+
+result = []
+for _, v in names.items():
+    old_names = v.names[:-1]
+    new_name = v.names[-1]
+
+    for old_name in old_names:
+        if old_name == new_name:
+            # A file was renamed to its new name twice; don't redirect that
+            continue
+
+        if old_name in current_files:
+            # A file was recreated with a former name; don't redirect those
+            continue
+
+        result.append((old_name, new_name))
+
+for old_name, new_name in sorted(result):
+    print(f"{old_name} {new_name}")