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Rollup merge of #122123 - compiler-errors:object-trait-alias-bounds, r=oli-obk

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Don't require specifying unrelated assoc types when trait alias is in `dyn` type

Object types must specify the associated types for all of the principal trait ref's supertraits. However, we weren't doing elaboration properly, so we incorrectly errored with erroneous suggestions to specify associated types that were unrelated to that principal trait ref. To fix this, use proper supertrait elaboration when expanding trait aliases in `conv_object_ty_poly_trait_ref`.

**NOTE**: Please use the ignore-whitespace option when reviewing. This only touches a handful of lines.

r? oli-obk or please feel free to reassign.

Fixes #122118
This commit is contained in:
Guillaume Gomez 2024-03-07 15:07:09 +01:00 • committed by GitHub
commit bb582c6d0f
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4 changed files with 55 additions and 50 deletions
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80
compiler/rustc_hir_analysis/src/astconv/object_safety.rs
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@ -45,10 +45,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
dummy_self,
&mut bounds,
false,
// FIXME: This should be `true`, but we don't really handle
// associated type bounds or type aliases in objects in a way
// that makes this meaningful, I think.
OnlySelfBounds(false),
// True so we don't populate `bounds` with associated type bounds, even
// though they're disallowed from object types.
OnlySelfBounds(true),
) {
potential_assoc_types.extend(cur_potential_assoc_types);
}
@ -83,9 +82,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
let expanded_traits =
traits::expand_trait_aliases(tcx, trait_bounds.iter().map(|&(a, b)| (a, b)));
let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
.filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
if regular_traits.len() > 1 {
let first_trait = &regular_traits[0];
let additional_trait = &regular_traits[1];
@ -158,7 +156,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
for (base_trait_ref, span) in regular_traits_refs_spans {
let base_pred: ty::Predicate<'tcx> = base_trait_ref.to_predicate(tcx);
for pred in traits::elaborate(tcx, [base_pred]) {
for pred in traits::elaborate(tcx, [base_pred]).filter_only_self() {
debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", pred);
let bound_predicate = pred.kind();
@ -312,45 +310,39 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
})
});
let existential_projections = projection_bounds
.iter()
// We filter out traits that don't have `Self` as their self type above,
// we need to do the same for projections.
.filter(|(bound, _)| bound.skip_binder().self_ty() == dummy_self)
.map(|(bound, _)| {
bound.map_bound(|mut b| {
assert_eq!(b.projection_ty.self_ty(), dummy_self);
let existential_projections = projection_bounds.iter().map(|(bound, _)| {
bound.map_bound(|mut b| {
assert_eq!(b.projection_ty.self_ty(), dummy_self);
// Like for trait refs, verify that `dummy_self` did not leak inside default type
// parameters.
let references_self = b.projection_ty.args.iter().skip(1).any(|arg| {
if arg.walk().any(|arg| arg == dummy_self.into()) {
return true;
}
false
});
if references_self {
let guar = tcx.dcx().span_delayed_bug(
span,
"trait object projection bounds reference `Self`",
);
let args: Vec<_> = b
.projection_ty
.args
.iter()
.map(|arg| {
if arg.walk().any(|arg| arg == dummy_self.into()) {
return Ty::new_error(tcx, guar).into();
}
arg
})
.collect();
b.projection_ty.args = tcx.mk_args(&args);
// Like for trait refs, verify that `dummy_self` did not leak inside default type
// parameters.
let references_self = b.projection_ty.args.iter().skip(1).any(|arg| {
if arg.walk().any(|arg| arg == dummy_self.into()) {
return true;
}
false
});
if references_self {
let guar = tcx
.dcx()
.span_delayed_bug(span, "trait object projection bounds reference `Self`");
let args: Vec<_> = b
.projection_ty
.args
.iter()
.map(|arg| {
if arg.walk().any(|arg| arg == dummy_self.into()) {
return Ty::new_error(tcx, guar).into();
}
arg
})
.collect();
b.projection_ty.args = tcx.mk_args(&args);
}
ty::ExistentialProjection::erase_self_ty(tcx, b)
})
});
ty::ExistentialProjection::erase_self_ty(tcx, b)
})
});
let regular_trait_predicates = existential_trait_refs
.map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));