Update to cargo 0.19.0-nightly (994e552 2017-04-25)

[SimonSapin]

This should be unblocked now: #15852 (comment)

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This change is 

[highfive]

Heads up! This PR modifies the following files:

• @wafflespeanut: python/servo/command_base.py, python/servo/devenv_commands.py

[SimonSapin]

@bors-servo r=nox

[bors-servo]

📌 Commit f267ecb has been approved by nox

[bors-servo]

⌛ Testing commit f267ecb with merge aa77c73...

[bors-servo]

💔 Test failed - linux-dev

[SimonSapin]

error: compile-fail/privatize.rs:8: unexpected "error": '8:1: 8:33: multiple matching crates for `deny_public_fields` [E0464]'

error: compile-fail/privatize.rs:8: unexpected "error": '8:1: 8:33: can't find crate for `deny_public_fields` [E0463]'

I can reproduce locally, and mach clean works around the issue. I wonder if we should run that on the builders and move on, or try to find a proper fix…

[SimonSapin]

This is because compile tests use rustc with -L target/debug and -L target/debug/deps and rely of finding dependencies in these directories by name, whereas Cargo uses --extern name=path/to/something.rlib with exact file names. When upgrading Cargo, some hash changes, new .rlib files are created, and old ones are not removed by default.

Finding the proper paths to use with --extern in compile test seems like a lot of work and not worth it. So it’s got with the exceptional clean. I’d rather not SSH into each builder to do that and hope that homu and buildbot’s scheduling will work in my favor, and at the same time I’d rather not go back to cleaning on every single build.

So it sounds like we need something like Gecko’s CLOBBER file. ./mach clean would be run automatically as part of build jobs if the CLOBBER file has changed since the last build.

[bors-servo]

⌛ Testing commit f267ecb with merge 7368589fed4bbff3596af1d6c5488fed5a86c0e4...

[bors-servo]

💔 Test failed - arm32

[jdm]

@bors-servo: retry

[bors-servo]

⌛ Testing commit f267ecb with merge 4a6b939...

[bors-servo]

💔 Test failed - mac-dev-unit

[jdm]

@bors-servo: retry
#16644

[bors-servo]

⌛ Testing commit f267ecb with merge f128781...

[bors-servo]

☀️ Test successful - android, arm32, arm64, linux-dev, linux-rel-css, linux-rel-wpt, mac-dev-unit, mac-rel-css, mac-rel-wpt1, mac-rel-wpt2, windows-msvc-dev
Approved by: nox
Pushing f128781 to master...