docbuild fails while trying to build the reference manual

[cyrilbouvier]

Steps To Reproduce

Following the advice from the developer's manual, I tried:

sage --docbuild reference html

Expected Behavior

The reference manual is build

Actual Behavior

Sage returns the following error:

Error building the documentation.
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/cyril/src/sage-dev/src/sage_docbuild/__main__.py", line 534, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/cyril/src/sage-dev/src/sage_docbuild/__main__.py", line 524, in main
    for dirpath, dirnames, filenames in os.walk(builder.dir, topdown=False):
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen os>", line 348, in walk
TypeError: expected str, bytes or os.PathLike object, not partial

    Note: incremental documentation builds sometimes cause spurious
    error messages. To be certain that these are real errors, run
    "make doc-clean doc-uninstall" first and try again.

Additional Information

The problem seems to come from the fact that builder.dir is a partial function and cannot be accepted as argument of os.walk. The fact that it is a partial function comes from the __getattr__ method of the class AllBuilder in sage_docbuild/builders.py.
If I am not mistaken, the use of builder.dir comes from the following changes in PR #38185:

+         for dirpath, dirnames, filenames in os.walk(SAGE_DOC_SRC, topdown=False):
-         for dirpath, dirnames, filenames in os.walk(builder.dir, topdown=False):

This piece of code is only executed when the command line parameter --no-prune-empty-dirs is not used.

Environment

• OS: Debian
• Sage Version: 10.5.beta9

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide