Diagrams get crunched if rendered by CI

[paolobrasolin]

This happened to @jonsterling in https://github.com/jonsterling/math producing charming results such as

(source: https://categorytheory.zulipchat.com/#narrow/stream/241990-general.3A-values/topic/goals.20and.20questions/near/267181997)

The problem is twofold:

1. the first compilation happened without ghostscript (a hard requirement for the conversion happening via dvisvgm)
2. following compilations were skipped (even when I tried adding the dependency) because the sourcecode MD5 didn't change

The solution is simple:

1. add the system dependency -> 7db5f96
2. clear the cache artifacts

There's still no nice button to empty the cache, though!
We can easily circumvent that by sketching another essential feature...

Some files will modify the compilation output even if the sources (hence their hashes) don't change. Therefore, changes in these files should invalidate the cache. Let's start by including TeX Live configuration in the list of such files -> 2cad5c6

Whatever solution we think of for #1 we'll need to consider this side effect.
In fact, you'll want to include your macro files in the list @jonsterling.

[jonsterling]

@paolobrasolin I just moved to a different machine (which does have Ghostscript installed) and this is happening locally. Do you have any suggestions for how I should proceed?

[jonsterling]

Update: Although Ghostscript is installed, it seems not to be recognised by dvisvgm, since when I manually run dvisvgm --pdf ... I get:

ERROR: Ghostscript is required to process PDF files.

I think the problem is that Homebrew doesn't actually install libgs properly; obviously this is neither the fault of your code nor the fault of dvisgvm, but nonetheless it remains a pretty serious obstacle for ordinary people to use it. I wonder what we should do.

[jonsterling]

I've added some instructions to my README for Mac users who face this problem: jonsterling/math@edcc188

[paolobrasolin]

I think the best we can do is document the snags with the various OSs.
I have no MacOS machine right now, so thanks for the research! ❤️
Since this is a general issue with jekyll-antex I'll steal the info for its documentation.
Also, I'll try to extend its CI to cover MacOS if I can.