Recover on const impl<> X for Y

[coolreader18]

@leonardo-m mentioned that const impl Foo for Bar could be recovered from in #79287.

I'm not sure about the error strings as they are, I think it should probably be something like the error that expected_one_of_not_found makes + the suggestion to flip the keywords, but I'm not sure how exactly to do that. Also, I decided not to try to handle const unsafe impl or unsafe const impl cause I figured that unsafe impl const would be pretty rare anyway (if it's even valid?), and it wouldn't be worth making the code more messy.

[rust-highfive]

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[coolreader18]

I switched to using expected_ident_found for the base error.

[petrochenkov]

Could you move this code to a separate function in parser/diagnostics.rs?
That's where diagnostic or recovery code lives, so it's separated from the "reference parser" code describing the language.

[coolreader18]

Oh I only just realized that you asked to move it to diagnostics.rs; I just moved it under recover_const_mut which is still in parser/item.rs, there's other recover_* functions there as well.

[petrochenkov]

parser/item.rs, there's other recover_* functions there as well.

(The other function will also need to move to diagnostics.rs, but not in this PR.)

[petrochenkov]

Could you also squash commits into one after making all the changes?

[coolreader18]

Alrighty, squashed.

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit 1e27b65 has been approved by petrochenkov

[bors]

⌛ Testing commit 1e27b65 with merge a428dd84d4e3cb80da7a395a0a047b1adf52677d...

[bors]

💔 Test failed - checks-actions

[petrochenkov]

LINK : fatal error LNK1201: error writing to program database 'D:\a\rust\rust\build\i686-pc-windows-msvc\test\run-make-fulldeps\relocation-model\relocation-model\foo.pdb'; check for insufficient disk space, invalid path, or insufficient privilege

Looks spurious.
@bors retry

[bors]

⌛ Testing commit 1e27b65 with merge 057937b...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 057937b to master...