`"could not open format file latex"` / `"Access is denied" (os error 5)` when a directory named `LaTeX` exists relative to input file on Windows

[alexpacini]

Summary

On Windows (case-insensitive NTFS), tectonic fails with "could not open format file latex" / "Access is denied. (os error 5)" if a directory named LaTeX/ (or latex/, LATEX/, etc.) exists relative to the input .tex file's location.

• What are those format files?

Environment

• OS: Windows 11 (NTFS, case-insensitive)
• Tectonic: 0.15.0
• Bundle: tlextras-2022.0r0.tar (default v33)

Steps to reproduce

mkdir C:\test-tectonic\LaTeX
Set-Content C:\test-tectonic\test.tex "\documentclass{article}`n\begin{document}`nHello`n\end{document}"
tectonic C:\test-tectonic\test.tex

Expected behaviour

Tectonic should compile test.tex successfully. The LaTeX/ directory is irrelevant: it is not a format file.

Actual behaviour

error: could not open format file latex
caused by: Access is denied. (os error 5)

Workarounds

1. Move the .tex file to a directory without a LaTeX/ sibling.
2. Use latexmk, pdflatex, luatex, xetex...