TeXpresso: proof-of-concept of interactive error reporting and rendering

[let-def]

Hi everybody,

I have been working on-and-off on TeXpresso, an interactive viewer for LaTeX documents. It is powered by a fork of Tectonic (see let-def/tectonic), but it is only superficial changes. I want to keep the changes minimal and merge them at some point.

There is nothing specific to Tectonic in it: originally I had patched TeXlive/XeTeX, but Tectonic is much easier to work with, to build and to distribute. Thanks for the good work.

It is Linux/macOS/Unix only: the interactivity is built around the cute hack of forking the process near the part of the input being edited. This is not going to work natively on Windows: short-term, the best would be to use WSL; medium-term, WASM with a good VM would support all the needs. But long-term, if the feature is popular, the best is to implement snapshotting in XeTeX engine directly. However I have no time for such work in the near future: for the moment I will slow down development (focusing on bug fix and important missing features) -- I think it reached the sweet spot to maximize my comfort of using LaTeX without spending too much time on the tool.

Only Emacs integration is provided at the moment, though it should not be a lot of work to provide a Vim mode.
Finally, the DVI renderer is entirely custom and built on top of MuPDF. It supports enough features to make working with tikz and Beamer presentations comfortable.

Hope you will find it useful! (But keep in mind it is very "alpha" quality: it works on a few machines I have tested and regularly discover bugs and portability problems, and the installation process is finicky!)