NLL test for mutating &mut references

[ritiek]

As mentioned in #46361.

cc @nikomatsakis?

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[alexcrichton]

r? @nikomatsakis

[matthewjasper]

Should this be replacing this test?

[nikomatsakis]

Hmm, yes, a good point! Maybe we already had the test? I like how this test actually runs the result, though.

@ritiek care to merge the two tests?

[ritiek]

Sure! Where should we keep the merged test though? src/test/run-pass/nll/mutating_references.rs or src/test/run-pass/borrowck/borrowck-nll-iterating-and-updating.rs?

[nikomatsakis]

@ritiek I prefer the nll directory for now, I think

[ritiek]

OK. So now we have the merged test in src/test/run-pass/nll/mutating_references.rs.

[nikomatsakis]

@bors r+

@ritiek great!

[bors]

📌 Commit 06d123d has been approved by nikomatsakis

[nikomatsakis]

@bors rollup