Use Travis trusty infrastructure

[arcnmx]

Moves back away from docker but still uses the GCE infrastructure with a system-installed LLVM.

See http://docs.travis-ci.com/user/trusty-ci-environment/

[rust-highfive]

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[arcnmx]

I can't test this myself since my own account has a 50 minute build time limit, but generally docker just seemed kind of redundant even if it only maybe adds a few minutes to the build time. With Rust's special travis settings hopefully it builds!

Also, considering that travis has been blocked up for a while, someone might want to cancel these bors commit tests to help travis catch up to all PRs in a decent time.

[alexcrichton]

Hm so on one hand I kinda like using docker because it makes the builds very easily reproducible as well as clearly showing us what our dependencies are (I think the Travis images come with some extra goodies by default), but on the other hand it does seem like it may just be unnecessary here. I'm fine merging, just waiting on travis to report back!

[arcnmx]

Makes sense, I also considered the same thing (and wondered if I should keep the dockerfile around just in case). Travis does have a minimal image though, which should help with that concern. I'll give it a try after this queued build hits.

[frewsxcv]

You can use the addons > apt > packages feature in travis.yml files to specify apt deps instead of manually installing them if you want. We do that in servo

https://github.com/servo/servo/blob/master/.travis.yml

[frewsxcv]

More info here

http://docs.travis-ci.com/user/apt/

[arcnmx]

Ah right, I was doing that on the container infrastructure but moved to the commands on GCE. I'll see about reverting that back again.

EDIT: it doesn't look like the sources we need are whitelisted. Just pushed a version that uses the minimal GCE image instead.

[sanxiyn]

While we're at it, can we remove or revise "Real testing happens on http://buildbot.rust-lang.org/" comment? It was introduced in #26224 when Travis only ran "make tidy", therefore no real testing. Maybe "Testing also happens" etc.

[arcnmx]

Well, it's still correct in that buildbot tests all supported platforms while Travis only tests x86_64 Linux. It's at best supplemental smoke testing, though I'm open to suggestions for a better explanation there.

[alexcrichton]

OK looks like this passed just fine, so I'd be fine merging with the apt addons section that @frewsxcv mentioned!

[arcnmx]

I wasn't able to get the apt addon approach to work as the sources for trusty don't seem to be in their whitelist.

See my various attempts here >_>

[alexcrichton]

@bors: r+ 1181ca4

ah ok!

[bors]

⌛ Testing commit 1181ca4 with merge b69c39c...

[alexcrichton]

@bors: retry force

[bors]

⌛ Testing commit 1181ca4 with merge d8acb03...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt