Getting the LaTeX code for a matrix should not try to compile LaTeX

[orlitzky]

When you create a matrix and call latex() on it, its _latex_() method gets called, and these are its first two lines:

latex = sage.misc.latex.latex
matrix_delimiters = latex.matrix_delimiters()

But the matrix_delimiters() method returns,

_Latex_prefs._option['matrix_delimiters']

and that _option attribute is...

self.__option["engine"] = default_engine()[0]
self.__option["engine_name"] = default_engine()[1]
return self.__option

Finally, the default_engine() is determined by...

from sage.features.latex import pdflatex, xelatex, lualatex
if lualatex().is_present():
    return 'lualatex', 'LuaLaTeX'
if xelatex().is_present():
    return 'xelatex', 'XeLaTeX'
if pdflatex().is_present():
    return 'pdflatex', 'pdfLaTeX'
return 'latex', 'LaTeX'

And those feature tests try to compile some LaTeX, launching a heavy process all just to print \begin{array}\end{array}.

[user202729]

The way to fix this should be to make def _option returns a lazy dict of some sort. Not sure if the change will break something downstream though.