Change in 1.0.0 to add pathlib support for .save() breaks usage of io.BytesIO

[acaos]

Versions

• Python 3.7
• Werkzeug 1.0.0 (from PyPI)

Report

The addition of pathlib support to .save() from #1654 breaks the the ability to pass io.BytesIO objects to .save().

Previous behavior: Saving to an io.BytesIO object worked as expected.
Behavior in 1.0.0: An exception is thrown in fspath().

  File "/app/main.py", line 310, in extract_metadata
    files['metadata'].save(metadata_io)
  File "/app/.venv/lib/python3.7/site-packages/werkzeug/datastructures.py", line 3061, in save
    dst = fspath(dst)
TypeError: expected str, bytes or os.PathLike object, not _io.BytesIO

[Vermeille]

For now I'm using this workaround

# until https://github.com/pallets/werkzeug/issues/1733 is fixed
buf = io.BytesIO()
#request.files['photo'].save(buf)
from shutil import copyfileobj
copyfileobj(request.files['photo'].stream, buf, 16384)

[davidism]

Looks like we need to do some shuffling with the order we check the types and do the conversion, in order to continue to support file-like objects. Scheduled for 1.0.1, PRs welcome if anyone can work on a fix.