xelatex doesn't seem to like this change in the travis build!

Ah yes, my current system uses TeX Live 2017, where \includegraphics accepts the interpolation parameter. The CI system is running TeX Live 2013, which apparently didn't support this, so \includegraphics really was not a viable option back in 2012. I knew there was a reason :D.

Attempt to upgrade TeX Live used by Travis to 2015 by adding PPA ppa:jonathonf/texlive-2015 failed. Honestly, I don't really understand the point of the jonathonf texlive PPAs. They claim backport different texlive versions to older LTS, but those PPAs hardly contain any texlive packages.

Well xelatex claims to be the 2015 version: https://travis-ci.org/matplotlib/matplotlib/jobs/363726207#L2738

I think that's a lie though. The PPA doesn't provide anything significant beyond texlive-base. In particular, it provides neither texlive-xetex nor texlive-luatex. So those must be still coming from 14.04 and just pick up the new version string from texlive base?

Does this need to wait for more distros to have a more modern texlive? I'll mark needs upstream fix, though I know thats not quite the situation here...

In the real world I'd say the typically distributed TeX live version should be recent enough, it's just that Travis is stuck at the extremely old Ubuntu 14.04. Reading their comments on this they don't seem to consider upgrading to a newer version anytime soon and suggest using the Docker option of defining your own base image.

Is moving from Travis stock images to a Docker based setup something that is being considered for matplotlib?

@pwuertz no, but in principle open to one or more of the builds in the test matrix moving over.

@pwuertz I bumped to 3.2, but if you think it'll work on modern CI, feel free to bumpy back...

power-cycled to re-trigger CI, looks like travis and azure are both too old...

We probably should document #10963 (comment) ?

Superseded by #15150.