Remove long diagnostic for E0002

[jfirebaugh]

E0002 was merged into E0004 in #36909, and the long diagnostic for E0004 is sufficient to cover empty match expressions.

cc @GuillaumeGomez

r? @jonathandturner

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @jonathandturner (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[sophiajt]

Good catch

@bors r+ rollup

[bors]

📌 Commit c4abe9d has been approved by jonathandturner

[GuillaumeGomez]

Sorry, I have memory of an internal policy which wants to keep old error codes explanation (even unused ones). Maybe I'm wrong. If it's the case, I'll r+ this PR again as soon as I have confirmation.

@bors: r-

[sophiajt]

Pinging @brson to see if he can confirm the internal policy around keeping error code long explanations for errors that no longer exist

[GuillaumeGomez]

cc @brson

[bors]

☔ The latest upstream changes (presumably #36695) made this pull request unmergeable. Please resolve the merge conflicts.

[alexcrichton]

Closing due to inactivity, but feel free to resubmit with a rebase!

[jfirebaugh]

@alexcrichton If I rebase, will it actually move this PR along? AFAICT, it's waiting on comment from Powers That Be, not me.

[brson]

@GuillaumeGomez I'm not sure what current practice is, but keeping old error explanations around sounds like something I might advocate, since there may be existing URLS in the wild. Certainly the old codes must remain allocated and unused, if not documented.

I don't feel strongly either way, whether old descriptions are kept or removed, but it seems like we should be consistent. Perhaps you can just decide.

@jfirebaugh Sorry for the delay.

[brson]

It looks to me like previously we've just added a notice to the top of such errors: https://github.com/rust-lang/rust/blob/master/src/librustc_resolve/diagnostics.rs#L19.

So I think we should just add the line

## Note: this error code is no longer emitted by the compiler.

as the first line of this error code.

@jfirebaugh I understand if you aren't interested in making the change. If you are then please go ahead, otherwise I'll follow up later.

[alexcrichton]

@jfirebaugh ah sorry I should have read more closely! I was just some standard triage and clearing out the queue a bit. I've personally seen a good track record for resubmitted rather than revived PRs in the past, but I always love to be proven wrong!

[GuillaumeGomez]

Note: this error code is no longer emitted by the compiler.

@brson: I think this is a good compromise.
@jfirebaugh: Can you add the line at the beginning of the error explanation instead of removing it please?

[jfirebaugh]

Thanks for the help -- I'm going to have to move on to other priorities however.