Fix binder handling in unnecessary_to_owned

[Jarcho]

fixes #11952

The use of rebind instead of EarlyBinder::bind isn't technically needed, but it is the semantically correct operation.

changelog: None

[rustbot]

r? @Alexendoo

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[Alexendoo]

👍 @bors r+

[bors]

📌 Commit 27c5b21 has been approved by Alexendoo

It is now in the queue for this repository.

[bors]

⌛ Testing commit 27c5b21 with merge 29bdc8b...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Alexendoo
Pushing 29bdc8b to master...

[smoelius]

The use of rebind instead of EarlyBinder::bind isn't technically needed, but it is the semantically correct operation.

I think I've seen you make similar comments before (though I can't seem to find them).

When is rebind necessary? Or where do I read about when rebind is necessary?

[Jarcho]

A binder is a combination of the list of variables which have yet to be bound, and an item which contains those variables (e.g. a type). As a rough guide to the two functions; rebind is used to create a new binder with the same list of variables as another, and bind would be used when a new list of variables is being applied. This makes rebind an alternative to map when that gets complicated/impossible to use.

For EarlyBinder, bind doesn't require a bound variable list so using it when rebind should be used will make it harder to transition to actually storing the variable list if that ever becomes a thing. Binder::bind actually requires a bound variable list so this isn't as much of a problem there.

[smoelius]

For EarlyBinder, bind doesn't require a bound variable list so using it when rebind should be used will make it harder to transition to actually storing the variable list if that ever becomes a thing.

Makes perfect sense. Thanks!