Error codes new

[GuillaumeGomez]

Part of #42229.

cc @Susurrus@frewsxcv@QuietMisdreavus

[rust-highfive]

r? @pnkfelix

(rust_highfive has picked a reviewer for you, use r? to override)

[Susurrus]

This looks good. Only comment I have on the text is whether this should include stating what the type was of the "something" that was called. I don't know if that'd every be useful to the user who sees this error in debugging though.

[QuietMisdreavus]

I'm wondering what the purpose of making these different error codes is. It seems more like E0618 is just a special case of E0619 at the moment. The latter looks like a catch-all "you called something that can't be called" error, while the former is specifically about unit types? Would it be a problem to make them use the same error code?

[GuillaumeGomez]

@QuietMisdreavus: I was wondering about this and I think I'll go this way.

[aidanhs]

Bunch of travis failures e.g.

[00:40:40] error: /checkout/src/test/compile-fail/E0618.rs:16: unexpected "error": '16:5: 16:15: expected function, found `X` [E0618]'
[00:40:40] [00:40:40] error: /checkout/src/test/compile-fail/E0618.rs:16: expected error not found: expected function, found `X::Entry` [E0618]
[00:40:40] 

[GuillaumeGomez]

Fixed CI.

[QuietMisdreavus]

Looks good to me!

@bors r+

[bors]

📌 Commit f720e97 has been approved by QuietMisdreavus

[frewsxcv]

@bors rollup