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Rollup merge of #136205 - compiler-errors:len-3, r=BoxyUwU

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Properly check that array length is valid type during built-in unsizing in index

This results in duplicated errors, but this class of errors is not new; in general, we aren't really equipped to detect cases where a WF error due to a field type would be shadowed by the parent struct of that field also not being WF.

This also adds a note for these types of mismatches to make it clear that this is due to an array type.

Fixes #134352

r? boxyuwu
This commit is contained in:
Matthias Krüger 2025-01-29 15:29:41 +01:00 • committed by GitHub
commit e8289d801c
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13 changed files with 63 additions and 9 deletions
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3
compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
View file

@ -2769,6 +2769,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
ObligationCauseCode::SliceOrArrayElem => {
err.note("slice and array elements must have `Sized` type");
}
ObligationCauseCode::ArrayLen(array_ty) => {
err.note(format!("the length of array `{array_ty}` must be type `usize`"));
}
ObligationCauseCode::TupleElem => {
err.note("only the last element of a tuple may have a dynamically sized type");
}

2
compiler/rustc_trait_selection/src/traits/wf.rs
View file

@ -689,7 +689,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
self.require_sized(subty, ObligationCauseCode::SliceOrArrayElem);
// Note that the len being WF is implicitly checked while visiting.
// Here we just check that it's of type usize.
let cause = self.cause(ObligationCauseCode::Misc);
let cause = self.cause(ObligationCauseCode::ArrayLen(t));
self.out.push(traits::Obligation::with_depth(
tcx,
cause,