Add a distinct error code and description for "main function has wrong type"

[jfirebaugh]

Followup to #36915. Adds a distinct error code and description for the "main function has wrong type" variant of E0308.

[rust-highfive]

r? @nrc

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[nrc]

nit: don't need the { ... } in the signature

[nrc]

You'll need to use a fresh error code, rather than one that is already in use.

r=me with that and the nit above addressed.

[brson]

Just waiting on updates from @jfirebaugh.

Error code 318 seems to be already allocated. You'll need to define a new one in librustc/diagnostics.rs. make tidy will output the highest recorded error number in its output, and you can pick the next.

[bors]

☔ The latest upstream changes (presumably #37678) made this pull request unmergeable. Please resolve the merge conflicts.

[GuillaumeGomez]

For info, the actual biggest error code is E0570.

[jfirebaugh]

I thought I had picked a unique one but I guess somehow I didn't search the whole tree. Switch to E0330.

[GuillaumeGomez]

This is still the same issue: the E0330 exist**ed**.

[jfirebaugh]

No, it's not the same issue.

[GuillaumeGomez]

Then I don't understand... Like said, E0330 exist**ed** so you can't use it. Now please explain what I got wrong. :-/

[jfirebaugh]

@GuillaumeGomez Sorry for my tone, I was in a grouchy mood and should have waited to comment.

The CI failure this time was due to a test case that had not been updated to the new error code. I don't see any indications in the repository history that E0330 has ever been used. Am I missing something?

~/Development/rust $ git log -S E0330
commit 3efcdba6010e1062977e193302bac73acffae13e
Author: John Firebaugh <john.firebaugh@gmail.com>
Date:   Sun Nov 13 15:43:27 2016 -0800

    Missed one compile test

commit 6bb4b84806b48cbf14ed0f6223a9bc8ea66285be
Author: John Firebaugh <john.firebaugh@gmail.com>
Date:   Sun Oct 2 17:03:28 2016 -0700

    Add a distinct error code and description for "main function has wrong type"
~/Development/rust $ 

[GuillaumeGomez]

For some history reason, we don't reuse an error code. Then if it's lower than the actual highest error code I gave in a previous comment, then it has been used and shouldn't be reused. So even if you can't find it in the git logs, don't bother and create a new one higher than the actual highest one.

[steveklabnik]

ping @jfirebaugh , are you still interested in updating this PR?

[jfirebaugh]

No.