Use caching docker TravisCI infrastructure

[gracjan]

Example is here:

https://github.com/alanz/HaRe/blob/wip/.travis.yml

[gracjan]

Not nice:

Adding APT Sources (BETA)
Disallowing sources: cassou/emacs, ubuntu-elisp, gracjanpolak
If you require these sources, please review the source approval process at: https://github.com/travis-ci/apt-source-whitelist#source-approval-process
Installing APT Packages (BETA)
Disallowing packages: emacs23-el, emacs24-el, emacs-snapshot, emacs-snapshot-el
If you require these packages, please review the package approval process at: https://github.com/travis-ci/apt-package-whitelist#package-approval-process

[gracjan]

PPA whitelist requests:

• APT source whitelist request for ppa:gracjanpolak/ppa travis-ci/apt-source-safelist#166 (Trusty has texinfo 5.2)
• APT source whitelist request for ppa:ubuntu-elisp/ppa travis-ci/apt-source-safelist#165
• APT source whitelist request for cassou/emacs travis-ci/apt-source-safelist#164 (exists as cassou-emacs)

Package whitelist requests:

• APT whitelist request for emacs23-el travis-ci/apt-package-safelist#1334
• APT whitelist request for emacs24-el travis-ci/apt-package-safelist#1335
• APT whitelist request for emacs-snapshot travis-ci/apt-package-safelist#1336
• APT whitelist request for emacs-snapshot-el travis-ci/apt-package-safelist#1337 (seems to not be needed at all)

The above follows the process outlined here:

• https://github.com/travis-ci/apt-source-whitelist#source-approval-process
• https://github.com/travis-ci/apt-package-whitelist#package-approval-process

We need to wait until it is approved.

[gracjan]

After a change from 'precise' to 'trusty' there seems to be proper texinfo available.

There is no way to get emacs-snapshot for now, so there are choices:

• wait more until there is a package available
• ignore emacs-snapshot for now
• download binaries by some other means

[gracjan]

Flycheck builds emacs on every checkout:

https://raw.githubusercontent.com/flycheck/emacs-travis/master/emacs-travis.mk

It takes 15 to 20 minutes to build. I'm not willing to wait.

[gracjan]

Looks like Trusty support on Travis is broken at the moment: travis-ci/travis-ci#5262

[gracjan]

Looks like Travis decided to go for Google Compute Engine. In that case docker is not useful.