Pear requires a nightly or dev version of Rust

[publicocean0]

Compiling rocket v0.4.4
Compiling indexmap v1.3.2
Compiling ring v0.13.5
error: failed to run custom build command for pear_codegen v0.1.2

Caused by:
process didn't exit successfully: /mnt/c/data/develop/rust/rust2/target/debug/build/pear_codegen-fc224e597d476dfc/build-script-build (exit code: 101)
--- stderr
Error: Pear requires a nightly or dev version of Rust.
Installed version is: 1.42.0 (2020-03-09). Minimum required: 1.31.0-nightly (2018-10-05).
thread 'main' panicked at 'Aborting compilation due to incompatible compiler.', /home/d77154/.cargo/registry/src/github.51.al-1ecc6299db9ec823/pear_codegen-0.1.2/build.rs:31:13
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

warning: build failed, waiting for other jobs to finish...
error: build failed

[abedra]

👍 on this. If there's still a nightly build requirement the message should be updated to match a newer nightly. If we are past that because of language maturity it would be nice to not have to use nightly.

[SergioBenitez]

The message indicates the nightly required by pear, not rocket. The message continues to be correct for the time being and will disappear in a later release of pear that doesn't require nightly.

[jonmz]

Out of curiousity, could you probably clarify why a dev or nightly build is needed? I am stumbling upon the same problem using Rust 1.43.1 from 2020-05-04. What feature needed by Pear would be available in a nightly build from 2018 (and are still available in current nightly builds), but not in a current released version?

[rogusdev]

Why is this closed? The issue trivially obviously merits an explanation when 1.31 is required and 1.42 won't satisfy, nightly or no. What needs to be changed to support this without a nightly flag?

[jebrosen]

What feature needed by Pear would be available in a nightly build from 2018 (and are still available in current nightly builds), but not in a current released version?

pear uses the specialization feature, which is still unstable since several years now. Given the pace of the specialization feature, I expect pear will be modified to not need specialization before specialization is actually stabilized.

The issue trivially obviously merits an explanation when 1.31 is required and 1.42 won't satisfy, nightly or no.

This is not the case; any nightly since 2018-10-05 should work (excepting any individual buggy nightly builds). If the latest nightly doesn't work and it's not a regression in rustc, that should be reported as a separate issue.

[rogusdev]

So there are features in nightly that are not in stable despite the version increases?

[jebrosen]

Yes. Unstable language features are opt-in with the #![feature] attribute, which is only available in nightly builds. Once a feature is stabilized, which could take months or even years of work, the corresponding #![feature] attribute is unnecessary and the feature will be usable in the next Rust beta (up to 6 weeks later) and in the stable channel 6 weeks after that.

[rayrrr]

See rust-lang/rust#31844 and https://internals.rust-lang.org/t/idea-where-match-clauses/12309 for the latest details of the specialization situation.

[rayrrr]

Update: looks like #27 actually takes care of these issues. All that's needed is a release. See rwf2/Rocket#19 (comment)