BUG: sphinxdev CI failure

[bsipocz]

I haven't looked into the details yet:

https://github.com/astropy/sphinx-astropy/actions/runs/14198250147/job/39778585162

build finished with problems, 1 warning (with warnings treated as errors).
----------------------------- Captured stderr call -----------------------------
WARNING: The config value `linkcheck_allowed_redirects' has type `NoneType'; expected `dict'.
___________________________ test_intersphinx_toggle ____________________________

tmp_path = PosixPath('/private/var/folders/r1/4882c7yd7wx9hcpc__xp04_m0000gn/T/pytest-of-runner/pytest-0/test_intersphinx_toggle1')
capsys = <_pytest.capture.CaptureFixture object at 0x1058fdd10>

    def test_intersphinx_toggle(tmp_path, capsys):
    
        # Test the sphinx_astropy.ext.intersphinx_toggle extension
    
        generate_files(tmp_path)
    
        src_dir = str(tmp_path)
        html_dir = str(tmp_path / "html")
    
        status = build_main(argv=['-W', '-b', 'html', src_dir, html_dir, '-D',
                                  'disable_intersphinx=1'])
    
>       assert status == 0
E       assert 1 == 0

../../sphinx_astropy/tests/test_conf_v2.py:54: AssertionError
----------------------------- Captured stdout call -----------------------------

[pllim]

I asked upstream 🤞

• Warn on all redirects if linkcheck_allowed_redirects is an empty dictionary sphinx-doc/sphinx#13452 (comment)
• Possible regression in linkcheck_allowed_redirects default following PR 13452 sphinx-doc/sphinx#13462

[jayaddison]

From narrowing down the contents of the v2 conf: I think this somehow relates to pydata_sphinx_theme. Commenting out this line of code removes the linkcheck_allow_redirects error (although I admit: it's not what we should do, and also other errors are introduced by attempting that):

sphinx-astropy/sphinx_astropy/conf/v2.py

Line 255 in 9ee5275

html_theme = 'pydata_sphinx_theme'

(I also confirmed that the error remains after emptying the extensions list, to add a little more confidence in that theory)