Description
Describe the bug
PDF is wrong if sources contain usage of \mathbf with the uppercase Greek control sequences in math mode, and latex_engine is set to 'xelatex' or 'lualatex'. It is ok with default ('pdflatex') or Japanese documents.
Rendering is ok with HTML+MathJaX or also with HTML+math-as-images (html_math_renderer='imgmath').
How to Reproduce
.. math:: \mathbf{\Lambda\Gamma\Delta\alpha\gamma\delta}
and latex_engine='xelatex'.
Latexmk: Summary of warnings from last run of *latex:
=====Latex reported missing or unavailable character(s).
=====See log file for details.
Latexmk: ====Undefined refs and citations with line #s in .tex file:
Missing character: There is no ^^C (U+0003) in font [FreeSerifBold.otf]/OT:scri
Missing character: There is no ^^C (U+0003) in font [FreeSerifBold.otf]/OT:script=latn;language=dflt;!
Missing character: There is no ^^C (U+0003) in font [FreeSerifBold.otf]/OT:scri
Missing character: There is no ^^C (U+0003) in font [FreeSerifBold.otf]/OT:script=latn;language=dflt;!
Missing character: There is no ^^C (U+0003) in font [FreeSerifBold.otf]/OT:scri
Missing character: There is no ^^C (U+0003) in font [FreeSerifBold.otf]/OT:script=latn;language=dflt;!
Missing character: There is no ^^@ (U+0000) in font [FreeSerifBold.otf]/OT:scri
And 9 more --- see log file 'foo.log'
Latexmk: All targets (foo.pdf) are up-to-date
Expected output is
Environment Information
Python version: 3.12.3 (v3.12.3:f6650f9ad7, Apr 9 2024, 08:18:48) [Clang 13.0.0 (clang-1300.0.29.30)])
Python implementation: CPython
Sphinx version: 8.0.2
Docutils version: 0.20.1
Jinja2 version: 3.1.4
Pygments version: 2.18.0
Sphinx extensions
No response
Additional context
As explained in sympy/sympy#26877 (comment) the cause of the problem is our \usepackage{fontspec}. Arguably it should be \usepackage[no-math]{fontspec}. The no-math prevents fontspec from redefining \mathrm, \mathbf etc... to use the body text fonts. Only the legacy Old TeX font config can allow the latter commands to work on \Lambda et al (they do nothing on lowercase Greek letters, it is only the matter of the eleven uppercase Greek letters defined by TeX with associated control sequences).