LaTeX Template: Improve package selections

[adunning]

Changes:

• Use Babel instead of Polyglossia for LuaLaTeX: there are a number of bugs in Polyglossia under this engine with common languages, e.g. polyglossia + lualatex: French punctuation spacing remains enabled after \textfrench{} reutenauer/polyglossia#182. (Most development appears to have moved from Polyglossia to Babel; it might make sense to make it the default for both LuaTeX and XeTeX before long.)
• Use xurl if available. Introduced with TeX Live 2018, this greatly improves the appearance of URLs by allowing them to break at additional points. (Run tlmgr update --all if you are seeing problems with this, as there were some bugs in the initial release.)
• Use bookmark if available, which can correct the levels of headings where hyperref cannot: see the KOMA-Script 3.26 release notes.
• Load xcolor if available. The xcolor package must be loaded before the footnote package, which we load to fix foonotes in tables. Closes footnote and xcolor do not commute #4861.
• Remove obsolete fixltx2e package (has no functionality with TeX Live 2015 or later).
• Reindent file.

This test demonstrates the changes:

pandoc -o test.pdf --pdf-engine=lualatex << EOT

Some text <http://dsf.tqsdatmdtdls.ctm/cudfsdvqfqll-ocd/bdcbcfqlf-lcclldh/cbsntwgqke-esbptb-vvylhy/zkhqnqidf-obedbacpf-lzlal-pxaccqa-gwki.lfof/> and another url: <http://osb.ccdngagkkg.raa/qrkxzvi/dxfsiaa/xidf-lata-dgdqmhp-uoxdl-vst-vcsbhl-aisdsasih-skl-aezb-fhixvyy-qqlachd-achhfc-koe-xgfqp-iyplcu-1.696884>.

[Bonjour!]{lang=fr}

Test!

EOT

With pandoc 2.5 template:

With changes:

[mb21]

Most development appears to have moved from Polyglossia to Babel; it might make sense to make it the default for both LuaTeX and XeTeX before long

I remember polyglossia being "marketed" as a newer replacement to babel. And when using XeTeX, the recommendation was to use polyglossia. You're saying babel has caught up with polyglossia and/or tackled whatever problems polyglossia was designed to solve?

[jgm]

For one recent issue with polyglossia/xelatex, see
pandoc/lua-filters#36
Special typography for French colons is applied in code blocks, and there seems to be no way to disable this short of switching to English for code blocks. I don't know if babel is any better in this respect.

[jgm]

What happens if they specify colorlinks but xcolor doesn't exist?
Previously we would have gotten a latex compilation failure, pointing to the need for xcolor.
What do we get in this case now?

[adunning]

Good point: if there are no visible links in the document, it will work even if colorlinks is specified.

It fails when the document tries to render a colour using the xcolor definitions: for example, in a document with a URL and colorlinks enabled:

! LaTeX Error: Undefined color `Blue'.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.69 \href{https://pandoc.org}{test url}

Is it worse, then, to require xcolor even in situations when it isn't needed, or to have an error message that doesn't explain the package is missing?

[adunning]

That verbatim issue does appear to be a bug specific to Polyglossia. I wonder if it would be worth making Polyglossia an option similar to how mathspec is handled right now. (Babel's support for RTL languages is even improving; here's a Hebrew example.) I've looked for a survey of which has broader language support at the moment, but haven't found anything.

For background, Babel is now part of the LaTeX core, supporting both XeTeX and LuaTeX, and has been improving steadily since it received a new maintainer in 2012. Meantime, the creator of Polyglossia is now inactive, and the current maintainer quite understandably has his hands full with managing the TeX hyphenation patterns. It would appear from all this that the eventual aim is make Babel a single interface for all languages and engines, though I'm not aware of a conscious effort to merge the two or any public statements on the matter.

[jgm]

Andrew Dunning <notifications@github.com> writes:

Is it worse, then, to require `xcolor` even in situations when it isn't needed, or to have an error message that doesn't explain the package is missing?

I like the basic principle that, if the latex code we generate *requires* a package, then the package should be unconditionally loaded in the preamble. If the package would merely improve output, but isn't required, then it's okay to load it if if exists. That will ensure that things fail in a way that gives the user the best clue as to what is going on. I'm not really concerned about documents with `colorlinks: true` failing even if they contain no links.

[adunning]

That does seem best; I've simplified the line to require xcolor. There are few situations in which it will be missing in any case.