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Fix 'assign to data in an index of' collection suggestions#152216

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GTimothy wants to merge 5 commits intorust-lang:mainfrom
GTimothy:map-diagnostics-fix
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Fix 'assign to data in an index of' collection suggestions#152216
GTimothy wants to merge 5 commits intorust-lang:mainfrom
GTimothy:map-diagnostics-fix

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@GTimothy GTimothy commented Feb 6, 2026 •
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fixes #150001
fixes rust-lang/rust-analyzer#16076
fixes #134917

The issues are threefold and linked:

  1. Assigning data to a collectionBTreeMap/HashMap suggests 3 solutions all marked as MachineApplicable
  2. The suggestions are slightly wrong with regards to their borrowing needs.
  3. The suggestions are not guaranteed to produce code that is valid, and suggestion number two is equivalent to an update, not an insertion.

This PR:

  • splits the large triple suggestion into three
  • sets them to MaybeIncorrect
  • automatically determines the required borrowing to use.

I think this solution may not be very elegant, expecially the key typechecking / borrowing part, but it works. I am however very open to any improvement/change :)

edit: edited to replace 'collection' with BTreeMap/HashMap'

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 6, 2026
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rustbot commented Feb 6, 2026

r? @JonathanBrouwer

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@GTimothy GTimothy force-pushed the map-diagnostics-fix branch from 8034656 to 2371906 Compare February 6, 2026 12:18
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GTimothy commented Feb 6, 2026 •
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oops, meant to title "Fix 'assign to data in an index of' map suggestions"
Should probably rename the commit too.

edit for clarity: for now, these suggestions only apply to BTreeMap and HashMap.

rust/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

Lines 657 to 661 in fef627b

fn suggest_map_index_mut_alternatives(&self, ty: Ty<'tcx>, err: &mut Diag<'infcx>, span: Span) {
let Some(adt) = ty.ty_adt_def() else { return };
let did = adt.did();
if self.infcx.tcx.is_diagnostic_item(sym::HashMap, did)
|| self.infcx.tcx.is_diagnostic_item(sym::BTreeMap, did)

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@GTimothy GTimothy marked this pull request as draft February 6, 2026 13:03
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 6, 2026
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@GTimothy GTimothy force-pushed the map-diagnostics-fix branch from 0fedd40 to 77c2a6e Compare February 14, 2026 15:36
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@GTimothy
Fix 'assign to data in an index of' collection suggestions
efb2ca0 
splits the large triple suggestion into three
sets them to MaybeIncorrect
automatically determines the required borrowing to use.
@GTimothy
restore missing case, method call on value of map
9b0864d
@GTimothy
rebless the ui tests
5d997ef
@GTimothy GTimothy force-pushed the map-diagnostics-fix branch from 77c2a6e to 5d997ef Compare February 16, 2026 09:48
@GTimothy GTimothy marked this pull request as ready for review February 16, 2026 19:03
@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 16, 2026
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GTimothy commented Feb 16, 2026

@JonathanBrouwer, I think this is ready for review. Do I need to change anything? Thanks in advance.

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JonathanBrouwer commented Feb 16, 2026

I'll take a look sometime in the next few days :)

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JonathanBrouwer requested changes Feb 20, 2026
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Thanks for your first contribution to rustc!
The idea looks good, just would like the code to be slightly nicer :)

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@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 20, 2026
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rustbot commented Feb 20, 2026

Reminder, once the PR becomes ready for a review, use @rustbot ready.

@rustbot rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Feb 20, 2026
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second version
193b59c 
- properly propose methods depending of the type relationship between
the index used and the map key.
- use whether key type is copy/clone to orient propositions.
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GTimothy commented Feb 23, 2026

thank you @JonathanBrouwer for your remarks. I had made a completely wrong assumptions about the types in questions.
I have completely reworked the PR in a much more elegant and correct way i think.

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GTimothy commented Feb 24, 2026

@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 24, 2026
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