Replace regex with string logic in thumbnail_to_original_filename

[Copilot]

thumbnail_to_original_filename used a compiled regex to split on the __ separator between source filename and thumbnail options. This is equivalent to a plain rsplit('__', 1).

Changes

• filer/utils/filer_easy_thumbnails.py: Replace RE_ORIGINAL_FILENAME regex and import re with pure-Python string logic:

  def thumbnail_to_original_filename(thumbnail_name):
      if '__' not in thumbnail_name:
          return None
      return thumbnail_name.rsplit('__', 1)[0]

• tests/test_utils.py: Add ThumbnailToOriginalFilenameTestCase covering:
  • No separator → None
  • Normal case: "foo.jpg__200x200_q85.jpg" → "foo.jpg"
  • Multiple separators in source: "a__b.jpg__200x200.jpg" → "a__b.jpg"
  • Leading separator: "__opts.jpg" → ""

Original prompt

Create a pull request in django-cms/django-filer (base branch: master) that removes the regex usage for extracting the original filename from a thumbnail filename in filer/utils/filer_easy_thumbnails.py.

Context:

• Current code (at least in commit 42090e83bca4a014948939d66722919a954b86ba) defines:
  • RE_ORIGINAL_FILENAME = re.compile(r"^(?P<source_filename>.*)__(?P<opts_and_ext>.*?)$")
  • thumbnail_to_original_filename(thumbnail_name) which does m = RE_ORIGINAL_FILENAME.match(thumbnail_name) and returns m.group(1) or None.
• Replace this with equivalent pure-Python string logic using the __ separator, matching the same behavior:
  • If "__" not in thumbnail_name, return None.
  • Otherwise, split on the last occurrence of "__" and return the part before it.
  • Preserve edge-case behavior: if thumbnail_name begins with "__", return "".

Implementation requirements:

1. Update thumbnail_to_original_filename to use rsplit('__', 1) rather than a regex.
2. Remove now-unused regex constant/imports if they become unused (e.g., import re and RE_ORIGINAL_FILENAME).
3. Add/adjust unit tests to cover:
   • No separator: "foo.jpg" -> None
   • Normal: "foo.jpg__200x200_q85.jpg" -> "foo.jpg"
   • Multiple separators in source filename: "a__b.jpg__200x200.jpg" -> "a__b.jpg"
   • Leading separator: "__opts.jpg" -> ""
4. Ensure formatting and linting match repository style.

Notes:

• The user referenced the file on master: https://github.com/django-cms/django-filer/blob/master/filer/utils/filer_easy_thumbnails.py.
• Please confirm the file’s current contents on master and adjust changes accordingly (it may differ from the older commit).

This pull request was created from Copilot chat.

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