## LaTeX2e kernel development moves to GitHub

The LaTeX team have two big jobs to do: maintaining LaTeX2e and working on LaTeX3 (currently as new packages on top of LaTeX2e). For quite a while now the LaTeX3 code has been available on GitHub as a mirror of the master repository. At the same time, the core LaTeX2e code was also available publicly using Subversion (SVN) via the team website. At least in the web view, the latter has always been a bit ‘Spartan’, both in appearance and in features (only the most recent revision could be seen).

Coupled to viewing the code for any project is tracking the issues. For LaTeX2e, the team have used GNATS for over twenty years. GNATS has served the team well, but like the web view is Subversion is showing its age.

We’ve now decided that the time is right to make a change. Eagle-eyed users will already have spotted the new LaTeX2e GitHub page, which is now the master repo for the LaTeX kernel. We’ve not yet frozen the existing GNATS database, but new bugs should be reported on GitHub. (For technical reasons, the existing GNATS bugs list is unlikely to be migrated to GitHub.)

Frank Mittelbach (LaTeX team lead developer) has written a short article on the new approach, which will be appearing in TUGboat soon. As Frank says, we hope that most users don’t run into bugs in the kernel (it is pretty stable and the code has been pushed pretty hard over the years), but this new approach will make reporting that bit easier and clearer.

Accompanying the move of LaTeX2e to GitHub, the LaTeX3 Subversion repository has also been retired: the master location for this is also now on GitHub. So everything is in a sense ‘sorted’: all in one place.

Of course, the team maintain only a very small amount of the LaTeX ‘ecosystem’: there are over 5000 packages on CTAN. To help users know whether a bug should be reported to the team or not, we have created the latexbug package.  An example using it:

\RequirePackage{latexbug}

\documentclass{article}

\begin{document}

Problems here

\end{document}



will give a warning if there is any code that isn’t covered by the team (and so should be reported elsewhere). We hope this helps bugs get to the right places as easily as possible.

I handled most of the conversion from Subversion to Git, and I’d like to acknowledge SubGit from TMate Software for making the process (largely) painless. As LaTeX is an open source project, we were able to use this tool for free. We used SubGit for the ‘live’ mirroring of LaTeX3 to GitHub for several years, and it worked flawlessly. The same was true for the trickier task of moving LaTeX2e: the repo history had a few wrinkles that we slightly more difficult to map to Git, but we got there.

The LaTeX Project have been making efforts over the past few years to update support in the LaTeX2e kernel for XeTeX and LuaTeX. Supporting these Unicode-enabled engines provide new features (and challenges) compared to the ‘classical’ 8-bit TeX engines (probably pdfTeX for most users). Over recent releases, the team have made the core of LaTeX ‘engine-aware’ and pulled a reasonable amount of basic Unicode data directly into the kernel. The next area we are addressing is font loading, or rather the question of what the out-of-the-box (text) font should be.

To date, the LaTeX kernel has loaded Knuth’s Computer Modern font in his original ‘OT1’ encoding for all engines. Whilst there are good reasons to load at least the T1-encoded version rather than the OT1 version, using an 8-bit engine using the OT1 version can be justified: it’s a question of stability, and nothing is actually out-and-out wrong.

Things are different with the Unicode engines: some of the basic assumptions change. In particular, there are some characters in the upper-half of the 8-bit range for T1 that are not in the same place in Unicode. That means that hyphenation will be wrong for words using some characters unless you load a Unicode font. At the same time, both LuaTeX and XeTeX have changed a lot over recent years: stability in the pdfTeX sense isn’t there. Finally, almost all ‘real’ documents using Unicode engines will be loading the excellent fontspec package to allow system font access. Under these circumstances, it’s appropriate to look again at the standard font loading.

After careful consideration, the team have therefore decided that as of the next (2017) LaTeX2e release, the standard text font loaded when XeTeX and LuaTeX are in use will be Latin Modern as a Unicode-encoded OpenType font. (This is the font chosen by fontspec so for almost all users there will no change in output.) No changes are being made to the macro interfaces for fonts, so users wanting anything other than Latin Modern will continue to be best served by loading fontspec. (Some adjustments are being made to the package to be ready for this.)

It’s important to add that no change is being made in math mode: the Unicode maths font situation is not anything like as clear as the text mode case.

There are still some details being finalised, but the general approach is clear and should make life easier for end users.

## LaTeX2e and e-TeX

LaTeX2e was released in 1994 and since then the LaTeX3 Project have been committed to keeping it working smoothly for users. That means balancing up keeping the code stable with fixing bugs and adding new features.

Back in 2003 the team announced that the e-TeX extensions would be used by the kernel when they were available. The new primitives offered by e-TeX make many parts of TeX programming easier and  often there’s no way in ‘classical’ TeX to get the same effect. As e-TeX was finalised in 1999, starting to use it seriously in around 2004 meant most people had access to them.

Since then, the availability and use of e-TeX has spread, and almost all users have them available. Indeed, the standard format-building routines for LaTeX have included them for many years. There are also a lot of packages on CTAN that use e-TeX, most obviously any using the expl3 programming language that the LaTeX3 Project have created.

The team had always meant to say at some stage that e-TeX was now required, and indeed thought we had until I checked over the official newsletters! So as of the next LaTeX2e release, scheduled for the start of 2017, the kernel will only build if e-TeX is enabled. For this release, we are likely to add a test for e-TeX but no actual use directly in the kernel, though in the future there will probably be more use of the extensions.

## Useful LaTeX2e programming macros

Martin Scharrer has put together a hand reference list of macros for programming LaTeX2e. This covers stuff in the LaTeX kernel itself, rather than add-ons such as etoolbox. This should be a real benefit to newer LaTeX programmers, as finding all of this information has in the past been quite awkward.