Currently the LaTeX documentation files must include a relative path to cactus.sty like so:

\usepackage{../../../../doc/latex/cactus}

which, assuming the “typical” directory layout, accidentally works both when calling pdflatex directly (and manually) on the LaTeX input file in the source code location and via the various -ThornDoc and -ThornGuide make targets.

This is however fragile and fails if e.g. the thorn lives in a git repository of its own so that the directory layout is:

Cactus
|
+- repos
   |
   +- ThornRepo
      |
      +- doc
         |
         +- documenation.tex

rather than the expected

Cactus
|
+- repos
   |
   +- ArrRepo
      |
      +- Thorn
         |
         +- doc
            |
            +- documenation.tex

or (the initially envisioned one assumes):

Cactus
|
+- arrangements
   |
   +- ArrangeMent
      |
      +- Thorn
         |
         +- doc
            |
            +- documenation.tex

One way to handle this is to use conditionals to try both locations:

\IfFileExists{../../../doc/latex/cactus.sty}
% then
{\usepackage{../../../doc/latex/cactus}}
% else
{\us
--

Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2638/documentationtex-assume-to-be-a-specific