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Rollup merge of #136311 - compiler-errors:vtable-fixes-2, r=lcnr

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Ensure that we never try to monomorphize the upcasting or vtable calls of impossible dyn types

Check for impossible obligations in the `dyn Trait` type we're trying to compute its the vtable upcasting and method call slots.

r? lcnr
This commit is contained in:
Matthias Krüger 2025-02-06 13:09:58 +01:00 • committed by GitHub
commit b62f318a3b
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2 changed files with 47 additions and 5 deletions
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26
compiler/rustc_trait_selection/src/traits/vtable.rs
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@ -318,9 +318,17 @@ pub(crate) fn first_method_vtable_slot<'tcx>(tcx: TyCtxt<'tcx>, key: ty::TraitRe
bug!();
};
let source_principal = tcx.instantiate_bound_regions_with_erased(
source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self),
source.principal().unwrap().with_self_ty(tcx, key.self_ty()),
);
// We're monomorphizing a call to a dyn trait object that can never be constructed.
if tcx.instantiate_and_check_impossible_predicates((
source_principal.def_id,
source_principal.args,
)) {
return 0;
}
let target_principal = ty::ExistentialTraitRef::erase_self_ty(tcx, key);
let vtable_segment_callback = {
@ -373,19 +381,27 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
let (source, target) = key;
// If the target principal is `None`, we can just return `None`.
let ty::Dynamic(target, _, _) = *target.kind() else {
let ty::Dynamic(target_data, _, _) = *target.kind() else {
bug!();
};
let target_principal = tcx.instantiate_bound_regions_with_erased(target.principal()?);
let target_principal = tcx.instantiate_bound_regions_with_erased(target_data.principal()?);
// Given that we have a target principal, it is a bug for there not to be a source principal.
let ty::Dynamic(source, _, _) = *source.kind() else {
let ty::Dynamic(source_data, _, _) = *source.kind() else {
bug!();
};
let source_principal = tcx.instantiate_bound_regions_with_erased(
source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self),
source_data.principal().unwrap().with_self_ty(tcx, source),
);
// We're monomorphizing a dyn trait object upcast that can never be constructed.
if tcx.instantiate_and_check_impossible_predicates((
source_principal.def_id,
source_principal.args,
)) {
return None;
}
let vtable_segment_callback = {
let mut vptr_offset = 0;
move |segment| {