non_exhaustive_omitted_patterns lint is unstable

[dhardy]

According to #1067, this lint was to be stabilised in Rust 1.57. It is not stable yet according to the tracking issue.

Maybe #1067 should be reverted?

[dtolnay]

I think this is fine. All you need is some build able to discover when match arms are missing. It doesn't have to work in every toolchain in your CI in order for you to find out; the set of enum variants in the same version of syn is not gonna be different on your other compilers.

If you require that your stable build is the one that detects missing match arms, you would need to follow up with the compiler folks about getting the lint stabilized.

[dhardy]

I think it is a step backwards, considering the previous solution worked just fine. But never mind.

[dtolnay]

I think it is a step forward because it's no longer possible for a crate to break its downstream users when a variant gets added.