Regression in 5 crates in 1.26: the trait bound is not satisfied

[pietroalbini]

There are a few crates that are failing to build on Rust 1.26 with the error the trait bound '###' is not satisfied. A lot of those errors seems to be related with !.

• bismuth regressed from stable to beta (build log) cc @olson-sean-k
• cucumber regressed from stable to beta (build log) cc @acmcarther
• plexus 0.0.1 regressed from stable to beta (build log) - already fixed in plexus 0.0.9
• rspec regressed from stable to beta (build log) cc @mackwic
• td_rredis regressed from stable to beta (build log) cc @tickbh

[mackwic]

thanks for the notification @pietroalbini ! Can I have the error log for rspec ?

[pietroalbini]

Woops! Forgot to add the link for that crate. Thanks for pointing that out! rspec report

[mackwic]

What is even ! ? I don't understand this error 😕

[pietroalbini]

What is even ! ? I don't understand this error 😕

The ! type is the "never" type, specified in RFC 1216 and stabilized in 1.26. It basically means "this return value is unreachable". In your case, that's the value returned by panic!.

[Mark-Simulacrum]

Errors related to ! might not be worth fixing just yet as I believe we're planning to revert that stabilization.

[acmcarther]

cucumber crate author here:

I wasn't able to replicate this from what I gleamed in the linked logs:

$ git clone git@github.com:acmcarther/cucumber && cd cucumber
$ rustup toolchain install beta-2018-04-06-x86_64-unknown-linux-gnu 
$ rustup default beta-2018-04-06-x86_64-unknown-linux-gnu
$ CARGO_INCREMENTAL=0 RUST_BACKTRACE=full RUSTFLAGS=--cap-lints=warn cargo test --no-run --frozen
# Build succeeds

Absent an actual reproduction though, I suspect dropping return from my return panic will probably resolve the issue in my crate.

[hawkw]

We're also seeing this when buillding h2 against nightly: hyperium/h2#257.

[pietroalbini]

This will be fixed after #50121 (reverting the stabilization) is merged and backported into beta.