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Lower struct patterns and struct expressions with unnamed fields #121553

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frank-king
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@frank-king frank-king commented Feb 24, 2024

This implements #49804.

Goals:

  • pattern matching with unnamed fields
    • check field conflict/absent errors
    • lower to THIR
  • struct expressions with unnamed fields
    • check field conflict/absent errors
    • lower to THIR

Non-Goals (will be in the next PRs)

  • capturing generic params for the anonymous ADTs from the parent ADT
  • rustdoc support of unnamed fields and anonymous ADTs

r? @davidtwco

@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 24, 2024
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@rustbot author

@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 24, 2024
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@rustbot label F-unnamed_fields

@rustbot rustbot added the F-unnamed_fields `#![feature(unnamed_fields)]` label Feb 24, 2024
@clubby789
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cc #121757, which I believe isn't currently fixed by these changes

@davidtwco
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cc #121757, which I believe isn't currently fixed by these changes

I've submitted a fix for this in #121975

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Some first pass review comments

&'tcx ty::FieldDef,
// The inner-most field type
Ty<'tcx>,
)> {
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This should be a type.

match mentioned {
Some((idx, _need_recheck @ true)) => {
// Check the only mentioned field of the union again,
// really collecting the unamed fields.
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Suggested change
// really collecting the unamed fields.
// really collecting the unnamed fields.


error: union patterns should have exactly one field
--> $DIR/union-fields-2.rs:17:9
|
LL | let U { a, b } = u;
| ^^^^^^^^^^
|
note: there are multiple fields from this union
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Suggested change
note: there are multiple fields from this union
note: multiple fields from this union are matched but the union can only be one at a time

Something a bit more verbose like this might be better.

@@ -50,6 +50,11 @@ pub struct TypeckResults<'tcx> {
/// `_(2).field`.
nested_fields: ItemLocalMap<Vec<(Ty<'tcx>, FieldIdx)>>,
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Can field_maps replace this?

return self.collect_unmentioned(
variant.fields.iter().skip(idx.index()).take(usize::MAX),
collect_unmentioned,
) || has_mentioned;
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I think the implementation of this check is a bit more complex than it needs to be I'm not sure why you need to go into collect_unmentioned here rather than just add to unmentioned_fields from this loop.

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Or rather, if there are unmentioned fields in one call to this function, then we could just queue up a UnionPatUnmentioned like you do for the other errors.

// In case of the multiple fields from the union are used,
// we do not collect those fields to report unmentioned errors.
self.check_struct_variant(nested_adt_def.non_enum_variant(), false)
.then_some((idx, /* need_recheck */ true))
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Similarly, I'm not sure that it's that big of a deal if we report an error for unmentioned fields from two unnamed struct types of an unnamed union (instead of just one of them). It may not be worth the additional complexity this adds.

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bors commented Mar 6, 2024

☔ The latest upstream changes (presumably #122041) made this pull request unmergeable. Please resolve the merge conflicts.

@Dylan-DPC
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@frank-king any updates on this? thanks

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I'm sorry that I haven't got some time to work on this. I'm going to close it.

@frank-king frank-king closed this Aug 9, 2024
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6 participants