README.md

A LaTeX Cookbook, git and Continuous Delivery

Remember, a few hours of trial and error can save you several minutes of looking at the README.

This repository contains two documents:

1. This README in Markdown format. Using pandoc with the Eisvogel template (more on that later), it is converted into a PDF and made available for download (see also the badge on top of the project homepage):

   

   The README covers git and Continuous Delivery.

2. A LaTeX document, usable as a cookbook (different "recipes" to achieve various things in LaTeX) and also as a template.

   The LaTeX Cookbook PDF covers LaTeX-specific topics and instruction on compiling the LaTeX source using Docker. It is also available for download:

   

git

That being said, onto git. This README will not be exhaustive; there are numerous great tools to learn git out there. This is just a brief introduction. Eventually, following all the steps, a number of advantages will come to light:

• SSOT: a Single Source Of Truth for data. No more file trees looking like this:

  directory
  │   a.txt
  │   help.me.please
  │   Important-Document_2018_version1.pdf
  │   Important-Document_2018_version2.pdf
  │   Important-Document_2018_version3_final.pdf
  │   Important-Document_2018_version3_final_really.pdf
  │   Important-Document_2018_version3_final_really_I-promise.pdf
  │   Important-Document_2018_versionA.pdf
  │   Important-Document_2019-03-56.pdf
  │   Important-Document_2019-03-56_corrections_John-Doe.pdf
  │   Important-Document_2019-03-56_corrections_John-Doe_v2.pdf
  │   invoice.docx
  │   test - Copy (2).tex
  │   test - Copy.tex
  │   test.tex
  │
  └───old_stuff
          Screenshot 1999-09-03-15-23-15(1).bmp
          Screenshot 1999-09-03-15-23-15(2).bmp
          Screenshot 1999-09-03-15-23-15(3).bmp
          Screenshot 1999-09-03-15-23-15(3)_edited.bmp
          Screenshot 1999-09-03-15-23-15.bmp
  

  Instead, there is one working copy looking like this:

  directory
  │   .git (a hidden directory)
  │   a.txt
  │   Important-Document.pdf
  │   Properly-Named-Invoice.docx
  

  assuming that a.txt is actually needed. All the old junk and redundant copies have been pruned. However, nothing was lost. The entire history is contained in git, a Version Control System. The history is readily summoned anytime, if so required. Git calls this its log. Git works best (some would say only) on text-based files, but it can deal with images, PDFs etc., too.

  The history and everything else git needs is contained in its .git directory, which is hidden on both Linux and Windows. Everything else in directory, so in this case a.txt, Important-Document.pdf and Properly-Named-Invoice.docx, is accessible as usual. There is no difference to how you would normally work with these files. They are on your local disk. Together, they are called the working tree.

  Therefore (provided that git is used correctly):

  1. Duplicate files are gone,
  2. The art of cumbersome file naming will finally be forgotten,
  3. Old stuff can be safely deleted; this cleans up the working tree and makes it clear which files are no longer needed. Only the currently needed files are visible, the rest is (retrievable!) history.

• File versioning and the ability to exactly match outputs (PDFs) to the source code that generated them.

• Accelerated bug fixing through git bisect, a binary search algorithm that helps pinpoint commits (stages of development) that introduced regressions.

• Collaboration: each contributor has a version of the source on their local machine. Adjustments are made there, and sent to a central, online repository if they are considered ready to be published. Git can also be used in a distributed fashion (its original strong suit), but we assume a remote repository on GitLab (which is very much similar to GitHub). Developers can then also fetch the latest changes from the remote and incorporate them into their local copy.

  Do not confuse GitHub, GitLab and others with the tool itself, git. Microsoft's GitHub is not synonymous to git. A crude, mostly wrong analogy would be: OneDrive is the platform you do collaboration, version control and sharing on. This is like GitHub (GitLab, ...). Office programs like Microsoft Word are used to create original content. This is like source code, as created in some editor of your choice. Word's built-in revision history, in conjunction with the process of naming files, for example 2020-05-13_Invoice_John-Doe-Comments_Final.docx (ISO-8601 oh yeah baby), would be git. It "only" does the version control, but is not a platform for source code.

• The remote repository also serves as a back-up solution. So do all the distributed local copies. At all points, there will be a workable copy somewhere. In general, git makes losing data extremely hard. If, or rather when, you do get into a fight with git about merging, pulling, rebasing, conflicts and the like, think of it as git protecting you and your work. Often, the reason for git "misbehaving" and making a scene is because it flat-out refuses to conduct an operation that would destroy unsaved changes. In the long run, this behavior is the desired one, as opposed to losing unsaved (in the git-lingo: uncommitted) data.

Getting Started

Download for Windows here. Install it and spam Next without reading the installation and warning prompts, as you always do.

For Linux, apt update && apt install git or whatever. You likely have it available already.

Then, somewhere on your machine:

# Create empty directory
$ mkdir test
# Go there
$ cd test
# Set up your git credentials; this will show as the 'Author' of your work
$ git config --global user.name "Foo Bar"
$ git config --global user.email "foo@bar.com"
# Initialize an empty git repository
$ git init
Initialized empty Git repository in ...
# Create some dummy file
$ echo "Hello World!" > test.txt
$ git status
On branch master

No commits yet

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        test.txt

nothing added to commit but untracked files present (use "git add" to track)
# Do as we are told, like good boys:
$ git add .
# There is now a change! The file is ready to be committed, aka "saved" into
# the history.
$ git status
On branch master

No commits yet

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)
        new file:   test.txt
$ git commit -m "Initial file!"
[master (root-commit) 3aaded0] Initial file!
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 test.txt
# Have a look at the history up to here:
$ git log --patch
commit 3aaded0365524e9c0cf7c3bc3cb72e1e993def74 (HEAD -> master)
Author: Foo Bar <foo@bar.com>
Date:   Mon Sep 28 15:29:25 2020 +0200

    Initial file!

diff --git a/test.txt b/test.txt
new file mode 100644
index 0000000..de39eb0
Binary files /dev/null and b/test.txt differ

And that is the gist of it. Next, you would want to create a project on GitLab or similar and connect that to your local repository. You can then sync changes between the two, enabling collaboration (or a bunch of other advantages if you keep to yourself).

There are numerous git GUIs available. They are great at visualizing the commit history (which can get convoluted, if you're doing it wrong), but also offer all the regular CLI functionality in GUI form. I have nothing to recommend here and am going to distract from this fact using this pretty git GUI image from here:

Git(Lab) and Continuous Delivery

GitLab is a platform to host git repositories. Projects on there can serve as git remotes. As mentioned, in this sense, it is like Microsoft's GitHub, the first large website to offer such a service (still by far the largest today). We use GitLab here because https://collaborating.tuhh.de/ is an instance of GitLab and therefore freely available to university members.

GitLab offers various features for each project. This includes a Wiki, an issue tracker and pull request management. Pull requests (PRs for short; GitLab calls these Merge Requests) are requests from outside collaborators who have forked and subsequently worked on a project. Forking projects refers to creating a full copy of the project in the own user space of collaborators. As such, they can then work on it, or do whatever else they want. If for example they add a feature, their own copy is now ahead of the original by that feature. To incorporate the changes back to the original, the original repository's maintainers can be requested to pull in the changes. This way, anyone can collaborate and help, without ever interfering with the main development in the original.

Continuous Delivery refers to continuously shipping out the finished "product". In this case, these are the compiled PDFs. This is done with the help of so-called Docker containers. The advantages are:

• collaborators no longer rely on their local tool chain, but on a unified, common, agreed-upon one. It is (usually) guaranteed to work and leads to the same, reproducible, predictable results for everyone.

  Docker (also usable locally, not only on the GitLab platform) helps reproduce results:

  • across space: results from coworkers in your office or from half-way across the globe.

    You no longer rely on some obscure, specific machine that happens to be the only one on which compilation (PDF production) works.

  • across time: if fixed versions are specified, Docker images allow programs, processes pipelines etc. from many years ago to run.

• If LaTeX documents become very long, full compilation runs can take dozens of minutes. This is outsourced and silently done on the remote servers, if Continuous Delivery is used. As such, for example, every git push to the servers triggers a pipeline which compiles the PDF and offers it for download afterwards. The last part could be called Continuous Deployment, albeit a very basic version.

One concrete workflow to employ this chain is to have a Dockerfile repository on GitHub, like this one. GitHub then integrates with DockerHub. It allows users to share images. As such, there is an image called alexpovel/latex on DockerHub. This image was built using the above GitHub Dockerfile and can be downloaded and run, yielding a live container. On every git push (that is, on every change) in the GitHub repo, this image is rebuilt. Given the size of TeXLive, this takes about on hour.

Refer to the Dockerfile itself (that Dockerfile is used to compile this very README to PDF via pandoc) for more details.

Enable Runner for the project

To build anything, we need someone to build for us. GitLab calls these build-servers runners. Such a runner does not materialize out of thin air. Luckily, in the case of collaborating.tuhh.de, runner tanis is available to us. Enable it (him? her?) for the project on the GitLab project homepage: Settings -> CI/CD -> Runners -> Enable Shared Runners. Otherwise, the build process will get 'stuck' indefinitely.

Add git info to PDF metadata

After retrieving a built PDF, it might get lost in the nether. That is, the downloader loses track of what commit it belongs to, or even what release. This is circumvented by injecting the git SHA into the PDF metadata. This allows you to freely hand out PDFs to people, for example for proof-reading or to editors of journals. You will be able to associate and pinpoint their remarks to a specific, reproducible version of the document. Note though that such a revision process is (much, much) better done using Pull Requests, provided the other party uses git and GitLab.

To identify versions in git, every object is uniquely identified by its hash (SHA256):

412ba291b6980ab21f912b5cdf01a13c6268d0ed

It is convenient to abbreviate the full SHA to a short version:

412ba291

Since a collision of even short hashes is essentially impossible in most use cases, we can uniquely identify states of the project by this short SHA. This is why commands like git show 412ba291 work (try it out; the SHA exists in this repository!). (As a side note: GitLab picks up on those hashes automatically, as shown in commit ccedcda0.) So if we have this SHA available in the PDF, never again will there be confusion about versions. The PDF will be be assignable to an exact commit. It can look like this (in Adobe Reader, evoke file properties with CTRL + D):

Using this approach, it is hidden and will not show up in print. You can of course also add the info to the document itself, so that it will be printed. But how do we get it there?

We have a chicken-and-egg problem: if we want to insert the current SHA into the current source files, we can't. While building the current PDF, we can only know the SHA of the previous commit. But, fear not, for GitLab has you covered:

During build-time, GitLab provides environment variables. These include things like CI_COMMIT_SHORT_SHA, which is exactly what we want. Now, we only need to get the contents of that variable into the LaTeX source, and finally the compiled PDF.

The LaTeX package hyperref can modify PDF metadata. In the LaTeX preamble, we can then use, for example,

\usepackage[pdfusetitle]{hyperref}% pdfusetitle reads from \author and \title
    \hypersetup{%
        pdfcreator={LaTeX with hyperref (\GitRefName{}, \GitShortSHA{})},
    }

to get metadata like in the PDF above. Navigate to the hyperref line in the class file to the see current implementation. Note that in LaTeX, you likely used \author{<author's name>} and \title{<document title>} somewhere in the preamble to generate a title page. hyperref's pdfusetitle option will use those values for the PDF metadata. Lastly, pdfcreator will fill the Application field we see above.

However, \GitRefName{} and \GitShortSHA{}} need to be defined first. This happens earlier in the preamble:

\directlua{
   dofile("lib/lua/envvar_newcommands.lua")
}

This runs, with the help of LuaTeX's Lua integration, some Lua code directly in LaTeX. Within Lua, os.getenv(<string> name) lets us retrieve environment variables, which are then turned into macros/control sequences (\newcommand) of a given name using token.set_macro(<string> csname, <string> content), see the LuaTeX reference on all the included Lua functionality provided by LuaTeX, on top of regular Lua.

Add PDF Download Button

On the top of the project page, we can add badges. That's how GitLab calls the small, clickable buttons. For real software developers, these might display code coverage and similar things. For, well... us, they can be used as a convenient way to download the built PDF. It can look like this (center left):

A little image (svg format) can be generated using shields.io. That only needs to be done once, and if you want to reuse the existing ones, here they are:

They have been embedded directly into the repository to not have to download them each time. They could also be embedded via their URL, for example https://img.shields.io/badge/Cookbook-Download-informational.svg. To add them to the project, go to: Settings -> General -> Badges. Give it a Name, enter the above file path or URL for the Badge image URL (or do whatever you want here), and finally enter the Link. This part is a bit tricky, since we need a dynamic URL that adapts to our path. For this, GitLab provides variables like %{project_path}. As such, the URL is (the hyphen in the middle is intentional):

https://collaborating.tuhh.de/%{project_path}/-/jobs/artifacts/%{default_branch}/raw/<filename>.pdf?job=build_pdf

The project_path is clear, the default_branch is just master. It visits the job artifacts on master and gets the PDF with the supplied filename. This filename has to be adjusted accordingly.

Note that the download is unavailable while a job is running. To avoid this, work on a git branch and leave master alone. Treat the PDF (or whatever it is) on master as the current stable version that only changes sometimes, not with every commit. For example, you can do your continuous business on a dev branch and then add a second button,

https://collaborating.tuhh.de/%{project_path}/-/jobs/artifacts/dev/raw/<filename>.pdf?job=build_pdf

Possible issues and pitfalls

Many nights were lost over issues involving GitLab CI/CD, but also plain LaTeX. Here is a non-exhaustive list --- a bit like a gallery of failure --- of the most common ones. Hopefully, it spares you some despair.

• You run into a similar error as:

  ! Package pgfplots Error: Sorry, the requested column number '1' in table 'dat.
  csv' does not exist!? Please verify you used the correct index 0 <= i < N..
  

  This can happen if you use pgfplotstable for plotting from tabular data, be it inline or from an outside file. If you use matlab2tikz, you might also run into the above error, since it potentially uses inline tables.

  In the class file, there is a line reading:

  \pgfplotstableset{col sep=comma}% If ALL files/tables are comma-separated

  This is a global default for all tables, assuming that they are comma-separated. The default is whitespace, which matlab2tikz uses, hence it breaks. You can override the column separator either in the above global option, or manually for each plot:

  % See https://tex.stackexchange.com/a/251245/120853
  \addplot3[surf] table [col sep=comma] {dat.csv};

• The job is working on Pulling docker image link to docker image for a while, and finally fails with

  ERROR: Job failed (system failure): Error response from daemon: No such container <some long container ID>

  Since, after we ensured the image indeed exists, know that cannot be the case, we Retry the job from the job page's top right corner:

  

  It should work afterwards (it never failed to restart after retrying for me). This will happen once in a while for some reason, perhaps caching. This has been an active issue for over two years now, with (at time of writing) the most recent comment within the last 24 hours. So, it is still in active discussion. It seems to have to do with caching. There does not seem to be a solution yet.

  This should be fixed now (at least, ever since the fix was applied, the issue no longer occurred), see here. This relies on the retry keyword in GitLab CI.

• When using package fontspec (or its derivative unicode-math), compilation fails with

  ! error:  (type 2): cannot find file ''
  !  ==> Fatal error occurred, no output PDF file produced!
  

  It is possible that the font cache is corrupted after moving fonts around. For example, if previously all fonts were in a flat ./fonts/ subdirectory of your document root, and then you decide to sort them into ./fonts/sans/ etc., the luatex cache will still point to the old ones.

  See here and also, similarly, here for a solution: delete the .lua and .luc files of the fonts in question from luatex-cache/generic/fonts/. For MiKTeX 2.9 on Windows 10, this was found in %USERPROFILE%\AppData\Local\MiKTeX\2.9\luatex-cache.

• When using package pgf-spectra compilation fails with

  LaTeX Error: File 'spectra.data.tex' not found.
  

  For a solution, see here, where it says:

  Hi

  texlive/2016/texmf-dist/tex/latex/pgf-spectra/pgf-spectra.sty

  ends with

  \input{spectra.data.tex}

  which generates a missing file error if the package is used, the data file is on ctan but it's misplaced in texlive as

  texlive/2016/texmf-dist/doc/latex/pgf-spectra/spectra.data.tex

  It should be in the tex tree not doc,

  David

  So, get spectra.data.tex from CTAN and place it accordingly. This can mean placing it in the project root. It would be better to put it next to the package file itself, pgf-spectra.sty, but this did not work even after refreshing the package database. This occurred on MiKTeX 2.9. TeXLive seemed fine in version 2019.

• The error is or is similar to:

  ! Undefined control sequence.
  l.52 \glsxtr@r
  

  With an *.aux file mentioned in the error message as well. Here, an auxiliary file got corrupted in an unsuccessful run and simply needs to be deleted. Do this manually or using latexmk -c.

• Concerning glossaries-extra:

  • Using \glssetcategoryattribute{<category>}{indexonlyfirst}{true}. For all items in <category>, it is meant to only add the very first reference to the printed glossary. If this reference is within a float, this breaks, and nothing shows up in the '##2' column.

    The way the document was set up, most symbols are currently affected. However, in an actual document, it is highly unlikely you will be referencing/using (with \gls{<symbol>}) symbols the first time in floating objects. Therefore, this problem is likely not a realistic issue.

  • In conjunction with subimport: That package introduces a neat structure to have subdirectories and do nested imports of *.tex files. But that might not be worth it, since it breaks many referencing functionalities in for example TeXStudio.

    More importantly, it seems to cause glossaries-extra to no longer recognize which references have occurred. We currently call selection=all in \GlsXtrLoadResources to load all stuff found in the respective *.bib file, regardless of whether it has actually been called at some point (using \gls{} etc.). This is a bit like if biblatex did not recognize cite commands and we just pulled every single item in the bibliography file. Some people use gigantic *.bib files, shared among their projects. If suddenly every entry showed up in the printed document despite not being referenced (be it a glossary or a bibliography item), chaos would ensue.

Appendix

Hints for source files

These are valid not only for LaTeX files, but most text-based source files:

• For the love of God, use UTF-8 or higher for text encoding. Stop using Windows 1252, Latin etc. Existing files can be easily updated to UTF-8 without much danger for regression (i.e., introducing errors).
• Put each sentence, or even part of a sentence, and each instruction onto its own line. This is very important to diff files properly, aka git diff. Generally, keep lines short.
• In a similar vein, use indentation appropriately. Indent using 4 spaces. There are schools of thought that advocate two spaces, or also one tab. Ultimately, that does not really matter. 'Four spaces' just seems to generally win the fight for a common coding style, bringing us to the next point.
• Be consistent. Even if you pull your own custom stuff, at least be consistent in doing so. This makes things predictable, the code will be easier to read, and also more easily changed programmatically. GNU/Linux and by extension Windows using Windows Subsystem for Linux has a very wide range of tools that make search, and search-and-replace, and various other operations for plain text files easy. The same is true for similar tools in IDEs. However, if the text is scattered and the style was mangled and fragmented into various sub-styles, this becomes very hard. For example, one person might use $<math>$ for inline-LaTeX math, another the (preferred) \(<math>\) style. Suddenly, you would have to search for both versions to find all inline-math. So stay consistent. If you work on pre-existing documents, use the established style. If you change it, change it fully, and not just for newly added work.