fix: Don't show duplicated adjustment hints for blocks, ifs and matches

[WaffleLapkin]

Before:

After:

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I want to improve adjustment hints, this is the first step :)

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit 7c9a85b has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7c9a85b with merge 1449204...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 1449204 to master...

[jonas-schievink]

Why are these coercions duplicated during type checking in the first place? To me that seems to be the better place to fix this.

[Veykril]

Thinking about this a bit, I don't think they are duplicating actually? The reborrows happen on every "pass" between blocks/expressions (which I believe matches rustc's behaviour, but would need to double check). Though the hints on the else block are obviously wrong, due to how we handle those block constructs.

[WaffleLapkin]

I don't think there is a meaningful difference between

1. { expr /* coercion */ } /* coercion */
2. { expr /* coercion */ }
3. { expr } /* coercion */

They all result in the same "<type of expr> coerces to <type of the whole expr>" relationship, coercing the coercion does nothing I think.

[WaffleLapkin]

For example in case of reborrows specifically I'm pretty sure &*&*a and &*a are the same. Because 'a <= '0 <= '1 and 'a <= '1 are equivalent.