For the record, the system Linux packages explicitly installed on GitHub Actions, but not Azure are:

• ccache
• libcairo2-dev
• libffi-dev
• libgeos-dev
• libgirepository1.0-dev
• libsdl2-2.0-0
• libxkbcommon-x11-0
• libxcb-cursor0
• libxcb-icccm4
• libxcb-image0
• libxcb-keysyms1
• libxcb-randr0
• libxcb-render-util0
• libxcb-xinerama0
• pkg-config
• qtbase5-dev

and vice versa:

• libgirepository-1.0-1
• poppler-utils

On macOS, GitHub Actions has:

• ghostscript
• gobject-introspection
• gtk4
• font-noto-sans-cjk
• inkscape

whereas for Azure its:

• ffmpeg
• imagemagick
• mplayer
• pkg-config
• font-noto-sans-cjk-sc
• xquartz

It also turns out that we never uploaded macOS coverage reports, so coverage is only down by 2 report from Linux. The coverage change shows that we lost:

• pdftocairo
• xpdf
• pdftops

I think these would have all come from poppler-utils. I don't think we are missing any backends, specifically. Possibly on macOS, we may also want to add ffmpeg? But that's definitely caught by Linux builds.

Do we know if xquartz is installed on GitHub or if it actually wasn't needed for Azure? It seems like the GUI-tests does not complain at least?

Interesting that a bit of the "executable not available"-tests lost coverage. Probably not worthwhile to have separate pipeline for those, but one may expect the minimum version test to handle them? Or maybe they are skipped earlier in the process? Is it worthwhile to setup a "minimum requirements" test (unless that is actually included in minimum versions)?

https://app.codecov.io/gh/matplotlib/matplotlib/pull/29171/blob/lib/matplotlib/backends/backend_pgf.py#L170

It looks like we support pdftocairo and gs for getting raster images out of pgf but always have pdftocairo installed so never test gs. If this is what was before, lets open an issue to look at it, if this is new can we get one job that uses ps (I have not chased things back, but I have a suspicion that pdftocairo is a system dependency of something we depend on for pgf).

Can we drop ffmpeg on the minimal deps run?

Do we know if xquartz is installed on GitHub or if it actually wasn't needed for Azure? It seems like the GUI-tests does not complain at least?

I think this may have been for GTK2. I don't recall if GTK3 used XQuartz, but GTK4 should be native. So I removed it and everything seems fine.

Interesting that a bit of the "executable not available"-tests lost coverage. Probably not worthwhile to have separate pipeline for those, but one may expect the minimum version test to handle them? Or maybe they are skipped earlier in the process? Is it worthwhile to setup a "minimum requirements" test (unless that is actually included in minimum versions)?

It looks like we support pdftocairo and gs for getting raster images out of pgf but always have pdftocairo installed so never test gs. If this is what was before, lets open an issue to look at it, if this is new can we get one job that uses ps (I have not chased things back, but I have a suspicion that pdftocairo is a system dependency of something we depend on for pgf).

These were from adding poppler-utils; I've left it out of the minimum versions build and now both of those code paths are touched.

Can we drop ffmpeg on the minimal deps run?

Yes, did that as well.