Add semverver CI

[robertbastian]

trafficstars

After 1.0 we have to be careful not to violate semver requirements. We can use the rust-semverver tool to generate a report for each PR.

[robertbastian]

Alternatively there's this crate as well https://github.com/Enselic/cargo-public-api

[pdogr]

rust-semverver errors out in some of our crates with the following errors

thread 'rustc' panicked at 'assertion failed: !self.in_new_crate(old)', src/mapping.rs:213:9

thread 'rustc' panicked at 'assertion failed: !value.has_escaping_bound_vars()', /rustc/4493a0f4724c0bae1436242d76cccc9c0a287b80/compiler/rustc_middle/src/ty/sty.rs:1024:9

[robertbastian]

Hmm I remember seeing that has_escaping_bound_vars regularly a while ago. Is your toolchain up to date? Can you try running with nightly?

[sffc]

Discussion:

• Run the tool manually for the 1.1 release
• Revisit CI for it in a future release

[sffc]

• @Manishearth - It's tricky to run semverver on CI, because we need to match it to a specific rustc version. It might involve adding another nightly. It is intended to be hands-off, and it is not supposed to be too expensive. What we could do is run it on cron job CI to keep the number of main CI jobs low.