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Fold vtable_trait_upcasting_coercion_new_vptr_slot logic into obligation processing.

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This commit is contained in:
Charles Lew
2021-08-18 12:45:18 +08:00
parent 1e605023ec
commit 6b1c52ff25
11 changed files with 137 additions and 87 deletions
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51
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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@@ -26,12 +26,13 @@ use crate::traits::Normalized;
use crate::traits::OutputTypeParameterMismatch;
use crate::traits::Selection;
use crate::traits::TraitNotObjectSafe;
use crate::traits::VtblSegment;
use crate::traits::{BuiltinDerivedObligation, ImplDerivedObligation};
use crate::traits::{
ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
ImplSourceDiscriminantKindData, ImplSourceFnPointerData, ImplSourceGeneratorData,
ImplSourceObjectData, ImplSourcePointeeData, ImplSourceTraitAliasData,
ImplSourceUserDefinedData,
ImplSourceTraitUpcastingData, ImplSourceUserDefinedData,
};
use crate::traits::{ObjectCastObligation, PredicateObligation, TraitObligation};
use crate::traits::{Obligation, ObligationCause};
@@ -42,6 +43,7 @@ use super::SelectionCandidate::{self, *};
use super::SelectionContext;
use std::iter;
use std::ops::ControlFlow;
impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
#[instrument(level = "debug", skip(self))]
@@ -121,7 +123,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
TraitUpcastingUnsizeCandidate(idx) => {
let data = self.confirm_trait_upcasting_unsize_candidate(obligation, idx)?;
Ok(ImplSource::Builtin(data))
Ok(ImplSource::TraitUpcasting(data))
}
}
}
@@ -694,7 +696,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
&mut self,
obligation: &TraitObligation<'tcx>,
idx: usize,
) -> Result<ImplSourceBuiltinData<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
) -> Result<ImplSourceTraitUpcastingData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>>
{
let tcx = self.tcx();
// `assemble_candidates_for_unsizing` should ensure there are no late-bound
@@ -706,16 +709,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
debug!(?source, ?target, "confirm_trait_upcasting_unsize_candidate");
let mut nested = vec![];
let source_trait_ref;
let upcast_trait_ref;
match (source.kind(), target.kind()) {
// TraitA+Kx+'a -> TraitB+Ky+'b (trait upcasting coercion).
(&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => {
// See `assemble_candidates_for_unsizing` for more info.
// We already checked the compatiblity of auto traits within `assemble_candidates_for_unsizing`.
let principal_a = data_a.principal().unwrap();
let source_trait_ref = principal_a.with_self_ty(tcx, source);
let target_trait_ref = util::supertraits(tcx, source_trait_ref).nth(idx).unwrap();
assert_eq!(data_b.principal_def_id(), Some(target_trait_ref.def_id()));
let existential_predicate = target_trait_ref.map_bound(|trait_ref| {
source_trait_ref = principal_a.with_self_ty(tcx, source);
upcast_trait_ref = util::supertraits(tcx, source_trait_ref).nth(idx).unwrap();
assert_eq!(data_b.principal_def_id(), Some(upcast_trait_ref.def_id()));
let existential_predicate = upcast_trait_ref.map_bound(|trait_ref| {
ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(
tcx, trait_ref,
))
@@ -762,7 +767,37 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
_ => bug!(),
};
Ok(ImplSourceBuiltinData { nested })
let vtable_segment_callback = {
let mut vptr_offset = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vptr_offset += ty::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
vptr_offset += util::count_own_vtable_entries(tcx, trait_ref);
if trait_ref == upcast_trait_ref {
if emit_vptr {
return ControlFlow::Break(Some(vptr_offset));
} else {
return ControlFlow::Break(None);
}
}
if emit_vptr {
vptr_offset += 1;
}
}
}
ControlFlow::Continue(())
}
};
let vtable_vptr_slot =
super::super::prepare_vtable_segments(tcx, source_trait_ref, vtable_segment_callback)
.unwrap();
Ok(ImplSourceTraitUpcastingData { upcast_trait_ref, vtable_vptr_slot, nested })
}
fn confirm_builtin_unsize_candidate(