tex-fast-recompile

A Python module to speed up TeX compilation.

This is similar to the mylatexformat TeX package that it works by "speed up" some "preamble", but unlike using "precompiled preamble" i.e. custom TeX format, this package works with every package including package that executes some Lua code, or load OpenType font.

Installation

It can be installed from PyPI or GitHub:

• https://pypi.org/project/tex-fast-recompile/
• https://github.com/user202729/tex-fast-recompile

You also need to install the helper TeX package fastrecompile.sty, which can be found in the tex/ directory. Refer to https://tex.stackexchange.com/q/1137/250119 for installation instruction.

(currently the TeX package is not available on CTAN)

Manual installation from source (GitHub)

In case I fix some bug in the latest version but forget to push to PyPI.

Run from the command-line:

pip install git+https://github.com/user202729/tex-fast-recompile

or alternatively download the code from GitHub by clicking "Code ⯆" green button → "Download ZIP" (at the moment), then unzip the file and from within the folder,

pip install -e .

The -e is an "editable" install, that is if you modify the source code in the folder, you don't need to reinstall the package.

Usage

Normal mode

If installed properly, an executable tex_fast_recompile should be available on your command-line.

Run tex_fast_recompile --help to view the available options.

For example you can use it as follows:

tex_fast_recompile pdflatex a.tex

to compile a.tex to a.pdf and automatically watch it on changes.

Usually prepending it to your LaTeX compilation command suffices.

LaTeXmk emulation mode

For compatibility with e.g. vimtex plugin, an executable tex_fast_recompile_latexmk is provided, which takes arguments similar to that of latexmk. (but it does not invoke bibliography/indexing commands/automatically detect changes to dependent files etc., and the simulation might not be complete)

Run tex_fast_recompile_latexmk --help to view the available options. (should be similar to latexmk's accepted options)

For VimTeX usage, putting the following configuration in .vimrc usually suffices:

let g:vimtex_compiler_latexmk = { 'executable' : 'tex_fast_recompile_latexmk' }

Note for Windows users

For yet-unknown reasons, file names containing non-ASCII characters are not supported. For example the following is invalid:

tex_fast_recompile pdflatex ≡.tex

As a workaround, the following appears to work:

python -m tex_fast_recompile pdflatex ≡.tex

Note for Vim users

If update performance appears slow, try disabling writebackup, or set backupcopy=yes. (this issue happened once for me, and I haven't been able to reproduce it so far. Alternatively just try restarting your computer.)

Limitations

• If VimTeX is used, the latexmk (emulation) is forcefully killed when compilation stops. In that case, the temporary directory is not cleaned, and over time it may clutter the temporary directory.

  (this has a partial workaround, that is new process spawned will clean up previous process' temporary directories)

• Any file \input in the preamble must not be changed. (when the preamble changes, the program will automatically detect that)

• You must not read from the terminal anywhere in the preamble, such as with functions \read -1 to ... or \ior_get_term:nN .... (if you're not sure what this mean, you should be safe)

• The latexmk emulation mode does not necessarily recompile the file sufficiently many times when references changed. (as such it might be convenient to use silence package to suppress the rerunfilecheck warnings such as:

\WarningFilter{latex}{Reference `}
\WarningFilter{latex}{Citation `}
\WarningFilter{latex}{There were undefined references}
\WarningFilter{latex}{Label(s) may have changed}
\WarningFilter{rerunfilecheck}{}

While the first filter may be overly broad, for the purpose of fast preview it isn't too important.)

Advanced notes

Explicitly specify preamble ending location

You can put \fastrecompileendpreamble on a single line to mark the end of the "fixed preamble" part.

Or equivalently, \csname fastrecompileendpreamble\endcsname (note that there must be no space before the \endcsname) -- this is the same as above, but will just silently do nothing instead of complaining about \fastrecompileendpreamble being not defined if this program is not used.

Note that:

• \fastrecompileendpreamble must appear at most once in the main file.
• There must be nothing else on the line that contains \fastrecompileendpreamble.
• SyncTeX features of the text part in the "preamble" may not be correct.

Normally, this is assumed to be right before the \begin{document} line (or \AtEndPreamble), but if you either

• use the --copy-output option (and only read the copied output), or
• there's no package that outputs something at the start of the document (such as hyperref), then you can move the \fastrecompileendpreamble to after the \begin{document} line.

Extra note

If you want to read the log file, refer to the help of --copy-log option.

It's possible to print out some content in the "preamble" part, but if you do so...

\documentclass{article}
\usepackage{fastrecompile}  % add the package here
% other preamble lines...
\begin{document}

123
\clearpage
\fastrecompileendpreamble
456

\end{document}

you must also use the --copy-output option if you want to view the resulting PDF.

Internal note

The module used to create a temporary file instead of \input the original file with begindocument/end hook, but with the --recorder flag then \currfileabspath will be wrong in the preamble, and @@input does not update the file name when the actual file is \input-ed.

With the handler moved to \AtEndPreamble instead of \AtBeginDocument there are some spurious messages... (not critical)

How does it work?

The principle is very simple. Notice that while the user want fast refresh, the file does not change very frequently.

As such, we start the compiler before the file has changed to process the "preamble", then when the file changed we continue processing the rest of the file.

A graph for illustration:

Before:

(each * represents a file change, |--.--| represents a compilation where the . marks where the preamble processing is done)

+----------------------------------------------------> Time
     *          *                *           *
     |--.--|    |--.--|          |--.--|     |--.--|

After:

+----------------------------------------------------> Time
     *          *                *           *
     |--.--|--. --|--.           --|--.      --|

It can be easily seen that after the change, it only takes 2 instead of 5 time units from when the file is saved to when the change is reflected in the PDF.