borrowck: suggest &mut *x for pattern reborrows
#152281
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| help: consider making the binding mutable if you need to reborrow multiple times | ||
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| LL | fn test(mut outer: &mut Option<i32>) { | ||
| | +++ | ||
| help: to reborrow the mutable reference, add `*` | ||
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| LL | match (&mut *outer, 23) { | ||
| | + |
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Here's a discussion point, maybe we should dedup help annotations.
I don't have strong preference and would like to follow someone's favor.
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In the past I've encountered cases where it isn't clear which of the two suggestions would be best, but gaining that certainty would require performing borrowck on the whole item with the two alternatives. For now, I find it ok to provide more than one suggestion, as long as it is clear that they are alternatives, and not that both need to be applied.
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How hard would it be to get the number of spans where we mention "cannot borrow as mutable"? Because that's pretty much the information we need to make the "you need to reborrow multiple times" determination to avoid the prior suggestion.
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| // We don't have access to the HIR to get accurate spans, but we can | ||
| // give a best effort structured suggestion. | ||
| err.span_suggestion_verbose( | ||
| source_info.span.with_hi(source_info.span.lo() + BytePos(5)), |
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Happy to see this go away.
| help: if there is only one mutable reborrow, remove the `&mut` | ||
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| LL - h(&mut b); | ||
| LL + h(b); | ||
| | |
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This is work that still needs to be addressed: we should be able to identify that there are more than one mutable reborrow and not suggest this.
Wait, in this case this is ok 🤦
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@bors r+ |
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Rollup of 7 pull requests Successful merges: - #152505 (Sync relnotes for stable 1.93.1) - #137487 (Stabilize `assert_matches`) - #152281 (borrowck: suggest `&mut *x` for pattern reborrows) - #151142 (Support ADT types in type info reflection) - #152477 (rustc-dev-guide subtree update) - #152488 (allow `deprecated(since = "CURRENT_RUSTC_VERSION")`) - #152491 (Remove unused `fluent-syntax` dependency from tidy)
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Fixes #81059
r? @estebank as you should have some context here, but feel free to re-assign if you don't have time to review right now.