Implement Termination for Result<Infallible, E>

[ibraheemdev]

As noted in #43301, Result<!, E> is not usable on stable.

[rust-highfive]

r? @kennytm

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[kennytm]

r? @rust-lang/libs-api

While the Termination trait itself is unstable, merging this PR means the following construct becomes insta-stable, so I think an FCP is needed:

fn main() -> Result<std::convert::Infallible, &'static str> {
    Err("error")
}

BTW it is strange that impl Termination for Infallible does not exist.

[KamilaBorowska]

BTW it is strange that impl Termination for Infallible does not exist.

There is no real need for that, fn main() -> ! { ... } works fine even on stable.

[yaahc]

@rfcbot merge

[rfcbot]

Team member @dtolnay has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @yaahc

Concerns:

• not-an-error resolved by Implement Termination for Result<Infallible, E> #88601 (comment)

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[Amanieu]

My understanding of Infallible is that it is a temporary workaround for the lack of ! for use as errors. In this case the Infallible is used in the Ok position, which is not really what it was meant for. I feel that we should push for the stabilization of ! instead of adding hacky workarounds like this.

@rfcbot concern not-an-error

[dtolnay]

While that may be the case, this change is not an everlasting API commitment. When Infallible becomes aliased to !, the impl here just goes away. I don't know of any downside to providing the impl prior to the ! stabilization going through.

[Amanieu]

I suppose that there is no downside to stabilizing this, so I'll remove my concern.

@rfcbot resolve not-an-error

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[yaahc]

@bors r+

[bors]

📌 Commit 2433d37 has been approved by yaahc