Update E0463 error message to new format

[paulfanelli]

Fixes#35934 as part of #35233

r? @jonathandturner

[rust-highfive]

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[sophiajt]

Rather than setting err_msg and using it later, you could instead set the label in the same condition. Maybe something like:

letmut err = struct_span_err!(self.sess,self.span,E0463,"can't find crate for `{}`{}",self.ident, add);
err.span_label(self.span,&format!("can't find crate"));
err

[sophiajt]

@paulfanelli - looks close. I added a comment of a way to tighten up the code.

[paulfanelli]

Oh man, I originally tried to code it that way, but I made a mistake, got a compiler error (it said there was a type mismatch between the if and else blocks) and thought that I couldn't code it that way. I tried your change -- and it works! Very nice. Definitely, learned a bunch of stuff from this one. Thx.

[paulfanelli]

I've updated the PR...

[sophiajt]

Yeah, that looks a lot better. I think we're almost there. One last thing - can you squash your two commits down to one? With that I think we're ready.

[paulfanelli]

Ok, I've squashed them together...and updated this PR.

[sophiajt]

Great, thanks.

@bors r+ rollup

[bors]

📌 Commit 58ced16 has been approved by jonathandturner