Add `tidy` to dependencies' CI

[edunham]

Creating a new issue to follow up on #861, since the packaging-tidy discussion took over that thread.

The servo_tidy package is now available on pip at https://pypi.python.org/pypi/servo_tidy/0.0.1 . Currently changes to it need to be deployed manually (secrets are in the "servo build machine secrets" doc), but we can automate the process once it becomes clearer how often we'll need to bump the version.

From examining the cargo.toml, I get this list of external dependencies that we should try to get tidy run on:
Ours (do these first)

• servo/gaol#26 [NEEDS TO BE TIDIED]
• servo/ipc-channel#67 [NEEDS TO BE TIDIED]
• https://github.com/servo/mozjs
• servo/rust-azure#222 [license and line length issues]
• servo/rust-freetype#39 [needs libc version pinned]
• servo/rust-layers#233 [license issues]
• servo/rust-mozjs#255 [license and line length issues]
• https://github.com/servo/webrender
• servo/webrender_traits#42

Others' (Discuss adding lint to their CI, or alternately run it ourselves)

• https://github.com/Ygg01/xml5ever
• https://github.com/aweinstock314/rust-clipboard
• https://github.com/browserhtml/browserhtml?branch=gh-pages
• https://github.com/emilio/angle?branch=servo
• https://github.com/ende76/brotli-rs
• https://github.com/energymon/energymon-rust.git
• https://github.com/energymon/energymon-sys.git
• https://github.com/huonw/simd
• https://github.com/jdm/tinyfiledialogs

[jdm]

I'm kind of ambivalent about asking authors of crates that are unrelated to Servo (except that we make use of them) to install our Servo-specific linter. For the license checks in particular, I wonder if we could make use of the crates.io API and fetch that data for local evaluation?

[edunham]

@jdm Good point. Do you think it'd be an appropriate compromise to ask the crate authors whether they'd be interested in running our lints, and if they aren't, run our own nightly check on clones of their repos to stay informed of how they compare? I expect that some maintainers will welcome the extra tests while others may disagree with the opinions enforced by the lints.

[jdm]

Most of our lints are for enforcing our code style rules (along with some common code nits). I don't think we gain any useful information by doing so, given how little we end up contributing to many of the crates we depend upon.

Another thing to point out is that Cargo.lock has the complete graph of our dependencies, which is a much larger list.

[wafflespeanut]

This is gonna be fun! 😄

[edunham]

The boilerplate for making tidy run in a non-python and containers+mac test suite is, in .travis.yml,

before_script:
    - export PATH=$HOME/.local/bin:/Users/travis/Library/Python/2.7/bin:$PATH
    - pip install servo_tidy --user `whoami`

script:
    - servo-tidy

[UK992]

@edunham now that tidy's license validation logic and config file landed, it is possible to update servo_tidy on pip?

[edunham]

@UK992 thanks for the reminder! Pushed new version to PyPI and wrote down how to do it this time, https://github.com/servo/servo/wiki/Infrastructure#tidy-on-pypi

[jdm]

This work isn't going to happen.