Make dblatex an optional dependency (issue 567480043 by firstname.lastname@example.org)
For some context: I played with the Docker containers shared by Han-Wen.
The one based on Ubuntu 16.04 (Xenial) is 974MB in size. Removing things
like git, nano, gdb and additional fonts (when purely interested in
automated building) gets me down to 809MB. Of the remaining, dblatex
seems to be one of the larger dependencies because it pulls in much of
TeXlive. After removing the image only weighs 667MB.
Given that it is used only for compiling a single test produced by
lilypond-book (nothing that ever shows up in the uploaded
documentation), I would also be happy to drop the dependency entirely.
The lost coverage amounts to not checking that the produced .xml file
can be processed by dblatex...
Make dblatex an optional dependency
Commit cfa910f1c1 in 2012 made it required unless disabling the doc
build. This is an overapproximation since dblatex is only required
for compiling the DocBook result of running lilypond-book on the file
input/regression/lilypond-book/suffix-lyxml.lyxml. If unavailable the
rules in make/lilypond-book-*.make have checks to only produce the
intermediate .xml file, without running dblatex to produce a .pdf.