testing/tools: Add a script to renumber objects in file order

I used this for patch set 11 on
https://pdfium-review.googlesource.com/c/pdfium/+/131550

Bug: none
Change-Id: If03d2d9b36bea60a9dd81d6efe2f178b3a826f02
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/131810
Reviewed-by: Nico Weber <thakis@google.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

testing/tools/renumber.py

diff --git a/testing/tools/renumber.py b/testing/tools/renumber.py
new file mode 100755
index 0000000..ccd011e
--- /dev/null
+++ b/testing/tools/renumber.py
@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+# Copyright 2025 The PDFium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Renumbers objects in a .in file consumed by fixup_pdf_template.py
+
+Takes a .in file and renumbers all objects therein so that they are numbered
+in the order they appear in in the file.
+"""
+
+import argparse
+import re
+import sys
+
+
+def renumber(contents):
+  OBJECT_PATTERN = r'{{object\s+(\d+)\s+(\d+)}}'
+
+  old_to_new = {
+      m.group(1): str(i)
+      for i, m in enumerate(re.finditer(OBJECT_PATTERN, contents), start=1)
+  }
+
+  def new_id(m):
+    return m.group(0).replace(m.group(1), old_to_new[m.group(1)])
+
+  contents = re.sub(OBJECT_PATTERN, new_id, contents)
+  contents = re.sub(r'\b(\d+)\s+\d+\s+R\b', new_id, contents)  # Update `n 0 R`.
+  return contents
+
+
+def main():
+  parser = argparse.ArgumentParser()
+  parser.add_argument('file')
+  args = parser.parse_args()
+
+  with open(args.file, 'r') as f:
+    contents = f.read()
+  contents = renumber(contents)
+  with open(args.file, 'w') as f:
+    f.write(contents)
+
+
+if __name__ == '__main__':
+  sys.exit(main())