fix regressions on assignment expressions

[lowr]

This is a follow-up PR on #12428. I'm not sure if this is everything I overlooked, so if there are more things that are not right, we may want to revert #12428.

This should also fix the increase of the type mismatches and the unknown types in diesel in the metrics introduced by #12428.

The regressions are:

• some coercions don't work in the ordinary (i.e. non-destructuring) assignments

  In order for coercions on ADT fields instantiations to work, lhs type has to be known before inferring rhs. feat: implement destructuring assignment #12428 changed the inference order, making rhs inferred before lhs, breaking the coercion, so I restored the original inference mechanism for the ordinary assignments.

  Note that this kind of coercion doesn't happen in destructuring assigments, because when they are desugared, the struct expression is first assigned to a temporary, which is then assigned to the assignee, which is not coercion site anymore.

• type mismatches on individual identifiers are not reported

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit 649e1f5 has been approved by Veykril

[bors]

⌛ Testing commit 649e1f5 with merge d1ac462...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing d1ac462 to master...

[lowr]

changelog skip

I think this shouldn't be on the changelog, as #12428 hasn't been released yet, but if maintainers think otherwise, please do edit this comment.

[lnicola]

I think this shouldn't be on the changelog, as #12428 hasn't been released yet, but if maintainers think otherwise, please do edit this comment.

We sometimes include fixup PRs together with the original one.

changelog fix fixup for 12428

[lowr]

Got it, thanks!