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Auto merge of #88135 - crlf0710:trait_upcasting_part_3, r=nikomatsakis 

Trait upcasting coercion (part 3)

By using separate candidates for each possible choice, this fixes type-checking issues in previous commits.

r? `@nikomatsakis`
This commit is contained in:
bors 2021-08-21 21:14:07 +00:00
parent b1928aa3b4 c22dfab215
commit d3e2578c31
19 changed files with 324 additions and 239 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
compiler/rustc_codegen_cranelift/src/unsize.rs
View File

@ -31,21 +31,10 @@ pub(crate) fn unsized_info<'tcx>(
if data_a.principal_def_id() == data_b.principal_def_id() {
return old_info;
}
// trait upcasting coercion
// if both of the two `principal`s are `None`, this function would have returned early above.
// and if one of the two `principal`s is `None`, typechecking would have rejected this case.
let principal_a = data_a
.principal()
.expect("unsized_info: missing principal trait for trait upcasting coercion");
let principal_b = data_b
.principal()
.expect("unsized_info: missing principal trait for trait upcasting coercion");
let vptr_entry_idx = fx.tcx.vtable_trait_upcasting_coercion_new_vptr_slot((
principal_a.with_self_ty(fx.tcx, source),
principal_b.with_self_ty(fx.tcx, source),
));
let vptr_entry_idx =
fx.tcx.vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
if let Some(entry_idx) = vptr_entry_idx {
let entry_idx = u32::try_from(entry_idx).unwrap();

15
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -150,19 +150,8 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
// trait upcasting coercion
// if both of the two `principal`s are `None`, this function would have returned early above.
// and if one of the two `principal`s is `None`, typechecking would have rejected this case.
let principal_a = data_a
.principal()
.expect("unsized_info: missing principal trait for trait upcasting coercion");
let principal_b = data_b
.principal()
.expect("unsized_info: missing principal trait for trait upcasting coercion");
let vptr_entry_idx = cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((
principal_a.with_self_ty(cx.tcx(), source),
principal_b.with_self_ty(cx.tcx(), source),
));
let vptr_entry_idx =
cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
if let Some(entry_idx) = vptr_entry_idx {
let ptr_ty = cx.type_i8p();

6
compiler/rustc_middle/src/query/mod.rs
View File

@ -987,9 +987,9 @@ rustc_queries! {
desc { |tcx| "finding all vtable entries for trait {}", tcx.def_path_str(key.def_id()) }
}
query vtable_trait_upcasting_coercion_new_vptr_slot(key: (ty::PolyTraitRef<'tcx>, ty::PolyTraitRef<'tcx>)) -> Option<usize> {
desc { |tcx| "finding the slot within vtable for trait {} vtable ptr during trait upcasting coercion from {} vtable",
tcx.def_path_str(key.1.def_id()), tcx.def_path_str(key.0.def_id()) }
query vtable_trait_upcasting_coercion_new_vptr_slot(key: (ty::Ty<'tcx>, ty::Ty<'tcx>)) -> Option<usize> {
desc { |tcx| "finding the slot within vtable for trait object {} vtable ptr during trait upcasting coercion from {} vtable",
key.1, key.0 }
}
query codegen_fulfill_obligation(

31
compiler/rustc_middle/src/traits/mod.rs
View File

@ -505,6 +505,9 @@ pub enum ImplSource<'tcx, N> {
/// Successful resolution for a builtin trait.
Builtin(ImplSourceBuiltinData<N>),
/// ImplSource for trait upcasting coercion
TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
/// ImplSource automatically generated for a closure. The `DefId` is the ID
/// of the closure expression. This is a `ImplSource::UserDefined` in spirit, but the
/// impl is generated by the compiler and does not appear in the source.
@ -540,6 +543,7 @@ impl<'tcx, N> ImplSource<'tcx, N> {
ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
| ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
ImplSource::TraitAlias(d) => d.nested,
ImplSource::TraitUpcasting(d) => d.nested,
}
}
@ -556,6 +560,7 @@ impl<'tcx, N> ImplSource<'tcx, N> {
ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
| ImplSource::Pointee(ImplSourcePointeeData) => &[],
ImplSource::TraitAlias(d) => &d.nested[..],
ImplSource::TraitUpcasting(d) => &d.nested[..],
}
}
@ -607,6 +612,13 @@ impl<'tcx, N> ImplSource<'tcx, N> {
substs: d.substs,
nested: d.nested.into_iter().map(f).collect(),
}),
ImplSource::TraitUpcasting(d) => {
ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
upcast_trait_ref: d.upcast_trait_ref,
vtable_vptr_slot: d.vtable_vptr_slot,
nested: d.nested.into_iter().map(f).collect(),
})
}
}
}
}
@ -652,6 +664,20 @@ pub struct ImplSourceAutoImplData<N> {
pub nested: Vec<N>,
}
#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
pub struct ImplSourceTraitUpcastingData<'tcx, N> {
/// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits, pointers to supertrait vtable will
/// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
/// within that vtable.
pub vtable_vptr_slot: Option<usize>,
pub nested: Vec<N>,
}
#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
pub struct ImplSourceBuiltinData<N> {
pub nested: Vec<N>,
@ -663,8 +689,9 @@ pub struct ImplSourceObjectData<'tcx, N> {
pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits; this is the start of
/// `upcast_trait_ref`'s methods in that vtable.
/// the base object trait and all supertraits, pointers to supertrait vtable will
/// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
/// in that vtable.
pub vtable_base: usize,
pub nested: Vec<N>,

5
compiler/rustc_middle/src/traits/select.rs
View File

@ -135,6 +135,11 @@ pub enum SelectionCandidate<'tcx> {
/// `rustc_infer::traits::util::supertraits`.
ObjectCandidate(usize),
/// Perform trait upcasting coercion of `dyn Trait` to a supertrait of `Trait`.
/// The index is the position in the iterator returned by
/// `rustc_infer::traits::util::supertraits`.
TraitUpcastingUnsizeCandidate(usize),
BuiltinObjectCandidate,
BuiltinUnsizeCandidate,

12
compiler/rustc_middle/src/traits/structural_impls.rs
View File

@ -30,6 +30,8 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSource<'tcx, N> {
super::ImplSource::Builtin(ref d) => write!(f, "{:?}", d),
super::ImplSource::TraitAlias(ref d) => write!(f, "{:?}", d),
super::ImplSource::TraitUpcasting(ref d) => write!(f, "{:?}", d),
}
}
}
@ -70,6 +72,16 @@ impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceBuiltinData<N> {
}
}
impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceTraitUpcastingData<'tcx, N> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(
f,
"ImplSourceTraitUpcastingData(upcast={:?}, vtable_vptr_slot={:?}, nested={:?})",
self.upcast_trait_ref, self.vtable_vptr_slot, self.nested
)
}
}
impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceAutoImplData<N> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(

11
compiler/rustc_mir/src/interpret/cast.rs
View File

@ -275,16 +275,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
return self.write_immediate(*val, dest);
}
// trait upcasting coercion
let principal_a = data_a.principal().expect(
"unsize_into_ptr: missing principal trait for trait upcasting coercion",
);
let principal_b = data_b.principal().expect(
"unsize_into_ptr: missing principal trait for trait upcasting coercion",
);
let vptr_entry_idx = self.tcx.vtable_trait_upcasting_coercion_new_vptr_slot((
principal_a.with_self_ty(*self.tcx, src_pointee_ty),
principal_b.with_self_ty(*self.tcx, src_pointee_ty),
src_pointee_ty,
dest_pointee_ty,
));
if let Some(entry_idx) = vptr_entry_idx {

10
compiler/rustc_query_impl/src/keys.rs
View File

@ -332,6 +332,16 @@ impl<'tcx> Key for Ty<'tcx> {
}
}
impl<'tcx> Key for (Ty<'tcx>, Ty<'tcx>) {
#[inline(always)]
fn query_crate_is_local(&self) -> bool {
true
}
fn default_span(&self, _: TyCtxt<'_>) -> Span {
DUMMY_SP
}
}
impl<'tcx> Key for &'tcx ty::List<ty::Predicate<'tcx>> {
#[inline(always)]
fn query_crate_is_local(&self) -> bool {

63
compiler/rustc_trait_selection/src/traits/mod.rs
View File

@ -28,6 +28,7 @@ use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_errors::ErrorReported;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
use rustc_middle::ty::{
@ -759,48 +760,38 @@ fn vtable_trait_first_method_offset<'tcx>(
pub fn vtable_trait_upcasting_coercion_new_vptr_slot(
tcx: TyCtxt<'tcx>,
key: (
ty::PolyTraitRef<'tcx>, // trait owning vtable
ty::PolyTraitRef<'tcx>, // super trait ref
Ty<'tcx>, // trait object type whose trait owning vtable
Ty<'tcx>, // trait object for supertrait
),
) -> Option<usize> {
let (trait_owning_vtable, super_trait_ref) = key;
let super_trait_did = super_trait_ref.def_id();
// FIXME: take substsref part into account here after upcasting coercion allows the same def_id occur
// multiple times.
let (source, target) = key;
assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
let vtable_segment_callback = {
let mut vptr_offset = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vptr_offset += COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
vptr_offset += util::count_own_vtable_entries(tcx, trait_ref);
if trait_ref.def_id() == super_trait_did {
if emit_vptr {
return ControlFlow::Break(Some(vptr_offset));
} else {
return ControlFlow::Break(None);
}
}
// this has been typecked-before, so diagnostics is not really needed.
let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
if emit_vptr {
vptr_offset += 1;
}
}
}
ControlFlow::Continue(())
}
let trait_ref = ty::TraitRef {
def_id: unsize_trait_did,
substs: tcx.mk_substs_trait(source, &[target.into()]),
};
let obligation = Obligation::new(
ObligationCause::dummy(),
ty::ParamEnv::reveal_all(),
ty::Binder::dummy(ty::TraitPredicate { trait_ref, constness: hir::Constness::NotConst }),
);
let implsrc = tcx.infer_ctxt().enter(|infcx| {
let mut selcx = SelectionContext::new(&infcx);
selcx.select(&obligation).unwrap()
});
let implsrc_traitcasting = match implsrc {
Some(ImplSource::TraitUpcasting(data)) => data,
_ => bug!(),
};
if let Some(vptr_offset) =
prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
{
vptr_offset
} else {
bug!("Failed to find info for expected trait in vtable");
}
implsrc_traitcasting.vtable_vptr_slot
}
pub fn provide(providers: &mut ty::query::Providers) {

5
compiler/rustc_trait_selection/src/traits/project.rs
View File

@ -1483,7 +1483,9 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
// why we special case object types.
false
}
super::ImplSource::AutoImpl(..) | super::ImplSource::Builtin(..) => {
super::ImplSource::AutoImpl(..)
| super::ImplSource::Builtin(..)
| super::ImplSource::TraitUpcasting(_) => {
// These traits have no associated types.
selcx.tcx().sess.delay_span_bug(
obligation.cause.span,
@ -1554,6 +1556,7 @@ fn confirm_select_candidate<'cx, 'tcx>(
| super::ImplSource::AutoImpl(..)
| super::ImplSource::Param(..)
| super::ImplSource::Builtin(..)
| super::ImplSource::TraitUpcasting(_)
| super::ImplSource::TraitAlias(..) => {
// we don't create Select candidates with this kind of resolution
span_bug!(

60
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
View File

@ -690,19 +690,50 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
debug!(?source, ?target, "assemble_candidates_for_unsizing");
let may_apply = match (source.kind(), target.kind()) {
match (source.kind(), target.kind()) {
// Trait+Kx+'a -> Trait+Ky+'b (upcasts).
(&ty::Dynamic(ref data_a, ..), &ty::Dynamic(ref data_b, ..)) => {
// See `confirm_builtin_unsize_candidate` for more info.
// Upcast coercions permit several things:
//
// 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`
// 2. Tightening the region bound, e.g., `Foo + 'a` to `Foo + 'b` if `'a: 'b`
// 3. Tightening trait to its super traits, eg. `Foo` to `Bar` if `Foo: Bar`
//
// Note that neither of the first two of these changes requires any
// change at runtime. The third needs to change pointer metadata at runtime.
//
// We always perform upcasting coercions when we can because of reason
// #2 (region bounds).
let auto_traits_compatible = data_b
.auto_traits()
// All of a's auto traits need to be in b's auto traits.
.all(|b| data_a.auto_traits().any(|a| a == b));
auto_traits_compatible
if auto_traits_compatible {
let principal_def_id_a = data_a.principal_def_id();
let principal_def_id_b = data_b.principal_def_id();
if principal_def_id_a == principal_def_id_b {
// no cyclic
candidates.vec.push(BuiltinUnsizeCandidate);
} else if principal_def_id_a.is_some() && principal_def_id_b.is_some() {
// not casual unsizing, now check whether this is trait upcasting coercion.
let principal_a = data_a.principal().unwrap();
let target_trait_did = principal_def_id_b.unwrap();
let source_trait_ref = principal_a.with_self_ty(self.tcx(), source);
for (idx, upcast_trait_ref) in
util::supertraits(self.tcx(), source_trait_ref).enumerate()
{
if upcast_trait_ref.def_id() == target_trait_did {
candidates.vec.push(TraitUpcastingUnsizeCandidate(idx));
}
}
}
}
}
// `T` -> `Trait`
(_, &ty::Dynamic(..)) => true,
(_, &ty::Dynamic(..)) => {
candidates.vec.push(BuiltinUnsizeCandidate);
}
// Ambiguous handling is below `T` -> `Trait`, because inference
// variables can still implement `Unsize<Trait>` and nested
@ -710,26 +741,29 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
(&ty::Infer(ty::TyVar(_)), _) | (_, &ty::Infer(ty::TyVar(_))) => {
debug!("assemble_candidates_for_unsizing: ambiguous");
candidates.ambiguous = true;
false
}
// `[T; n]` -> `[T]`
(&ty::Array(..), &ty::Slice(_)) => true,
(&ty::Array(..), &ty::Slice(_)) => {
candidates.vec.push(BuiltinUnsizeCandidate);
}
// `Struct<T>` -> `Struct<U>`
(&ty::Adt(def_id_a, _), &ty::Adt(def_id_b, _)) if def_id_a.is_struct() => {
def_id_a == def_id_b
if def_id_a == def_id_b {
candidates.vec.push(BuiltinUnsizeCandidate);
}
}
// `(.., T)` -> `(.., U)`
(&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => tys_a.len() == tys_b.len(),
(&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => {
if tys_a.len() == tys_b.len() {
candidates.vec.push(BuiltinUnsizeCandidate);
}
}
_ => false,
_ => {}
};
if may_apply {
candidates.vec.push(BuiltinUnsizeCandidate);
}
}
fn assemble_candidates_for_trait_alias(

172
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View File

@ -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))]
@ -118,6 +120,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let data = self.confirm_builtin_unsize_candidate(obligation)?;
Ok(ImplSource::Builtin(data))
}
TraitUpcastingUnsizeCandidate(idx) => {
let data = self.confirm_trait_upcasting_unsize_candidate(obligation, idx)?;
Ok(ImplSource::TraitUpcasting(data))
}
}
}
@ -685,6 +692,114 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
.map_err(|e| OutputTypeParameterMismatch(expected_trait_ref, obligation_trait_ref, e))
}
fn confirm_trait_upcasting_unsize_candidate(
&mut self,
obligation: &TraitObligation<'tcx>,
idx: usize,
) -> Result<ImplSourceTraitUpcastingData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>>
{
let tcx = self.tcx();
// `assemble_candidates_for_unsizing` should ensure there are no late-bound
// regions here. See the comment there for more details.
let source = self.infcx.shallow_resolve(obligation.self_ty().no_bound_vars().unwrap());
let target = obligation.predicate.skip_binder().trait_ref.substs.type_at(1);
let target = self.infcx.shallow_resolve(target);
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();
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,
))
});
let iter = Some(existential_predicate)
.into_iter()
.chain(
data_a
.projection_bounds()
.map(|b| b.map_bound(ty::ExistentialPredicate::Projection)),
)
.chain(
data_b
.auto_traits()
.map(ty::ExistentialPredicate::AutoTrait)
.map(ty::Binder::dummy),
);
let existential_predicates = tcx.mk_poly_existential_predicates(iter);
let source_trait = tcx.mk_dynamic(existential_predicates, r_b);
// Require that the traits involved in this upcast are **equal**;
// only the **lifetime bound** is changed.
let InferOk { obligations, .. } = self
.infcx
.at(&obligation.cause, obligation.param_env)
.sup(target, source_trait)
.map_err(|_| Unimplemented)?;
nested.extend(obligations);
// Register one obligation for 'a: 'b.
let cause = ObligationCause::new(
obligation.cause.span,
obligation.cause.body_id,
ObjectCastObligation(target),
);
let outlives = ty::OutlivesPredicate(r_a, r_b);
nested.push(Obligation::with_depth(
cause,
obligation.recursion_depth + 1,
obligation.param_env,
obligation.predicate.rebind(outlives).to_predicate(tcx),
));
}
_ => bug!(),
};
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(
&mut self,
obligation: &TraitObligation<'tcx>,
@ -701,58 +816,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let mut nested = vec![];
match (source.kind(), target.kind()) {
// Trait+Kx+'a -> Trait+Ky+'b (upcasts).
// Trait+Kx+'a -> Trait+Ky+'b (auto traits and lifetime subtyping).
(&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => {
// Upcast coercions permit several things:
//
// 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`
// 2. Tightening the region bound, e.g., `Foo + 'a` to `Foo + 'b` if `'a: 'b`
// 3. Tightening trait to its super traits, eg. `Foo` to `Bar` if `Foo: Bar`
//
// Note that neither of the first two of these changes requires any
// change at runtime. The third needs to change pointer metadata at runtime.
//
// We always perform upcasting coercions when we can because of reason
// #2 (region bounds).
// 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();
let principal_def_id_b = data_b.principal_def_id();
let existential_predicate = if let Some(principal_a) = principal_a {
let source_trait_ref = principal_a.with_self_ty(tcx, source);
let target_trait_did = principal_def_id_b.ok_or_else(|| Unimplemented)?;
let upcast_idx = util::supertraits(tcx, source_trait_ref)
.position(|upcast_trait_ref| upcast_trait_ref.def_id() == target_trait_did)
.ok_or_else(|| Unimplemented)?;
// FIXME(crlf0710): This is less than ideal, for example,
// if the trait is defined as `trait Foo: Bar<u32> + Bar<i32>`,
// the coercion from Box<Foo> to Box<dyn Bar<_>> is actually ambiguous.
// We currently make this coercion fail for now.
//
// see #65991 for more information.
if util::supertraits(tcx, source_trait_ref)
.skip(upcast_idx + 1)
.any(|upcast_trait_ref| upcast_trait_ref.def_id() == target_trait_did)
{
return Err(Unimplemented);
}
let target_trait_ref =
util::supertraits(tcx, source_trait_ref).nth(upcast_idx).unwrap();
let existential_predicate = target_trait_ref.map_bound(|trait_ref| {
ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(
tcx, trait_ref,
))
});
Some(existential_predicate)
} else if principal_def_id_b.is_none() {
None
} else {
return Err(Unimplemented);
};
let iter = existential_predicate
let iter = data_a
.principal()
.map(|b| b.map_bound(ty::ExistentialPredicate::Trait))
.into_iter()
.chain(
data_a

6
compiler/rustc_trait_selection/src/traits/select/mod.rs
View File

@ -1516,6 +1516,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| FnPointerCandidate
| BuiltinObjectCandidate
| BuiltinUnsizeCandidate
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { .. }
| TraitAliasCandidate(..)
| ObjectCandidate(_)
@ -1533,6 +1534,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| FnPointerCandidate
| BuiltinObjectCandidate
| BuiltinUnsizeCandidate
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { has_nested: true }
| TraitAliasCandidate(..),
ParamCandidate(ref cand),
@ -1562,6 +1564,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| FnPointerCandidate
| BuiltinObjectCandidate
| BuiltinUnsizeCandidate
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { .. }
| TraitAliasCandidate(..),
) => true,
@ -1573,6 +1576,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| FnPointerCandidate
| BuiltinObjectCandidate
| BuiltinUnsizeCandidate
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { .. }
| TraitAliasCandidate(..),
ObjectCandidate(_) | ProjectionCandidate(_),
@ -1646,6 +1650,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| FnPointerCandidate
| BuiltinObjectCandidate
| BuiltinUnsizeCandidate
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { has_nested: true }
| TraitAliasCandidate(..),
ImplCandidate(_)
@ -1654,6 +1659,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| FnPointerCandidate
| BuiltinObjectCandidate
| BuiltinUnsizeCandidate
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { has_nested: true }
| TraitAliasCandidate(..),
) => false,

3
compiler/rustc_ty_utils/src/instance.rs
View File

@ -381,7 +381,8 @@ fn resolve_associated_item<'tcx>(
| traits::ImplSource::Param(..)
| traits::ImplSource::TraitAlias(..)
| traits::ImplSource::DiscriminantKind(..)
| traits::ImplSource::Pointee(..) => None,
| traits::ImplSource::Pointee(..)
| traits::ImplSource::TraitUpcasting(_) => None,
})
}

39
src/test/ui/traits/trait-upcasting/correct-supertrait-substitution.rs Normal file
View File

@ -0,0 +1,39 @@
// run-pass
#![feature(trait_upcasting)]
#![allow(incomplete_features)]
trait Foo<T: Default + ToString>: Bar<i32> + Bar<T> {}
trait Bar<T: Default + ToString> {
fn bar(&self) -> String {
T::default().to_string()
}
}
struct S1;
impl Bar<i32> for S1 {}
impl Foo<i32> for S1 {}
struct S2;
impl Bar<i32> for S2 {}
impl Bar<bool> for S2 {}
impl Foo<bool> for S2 {}
fn test1(x: &dyn Foo<i32>) {
let s = x as &dyn Bar<i32>;
assert_eq!("0", &s.bar().to_string());
}
fn test2(x: &dyn Foo<bool>) {
let p = x as &dyn Bar<i32>;
assert_eq!("0", &p.bar().to_string());
let q = x as &dyn Bar<bool>;
assert_eq!("false", &q.bar().to_string());
}
fn main() {
let s1 = S1;
test1(&s1);
let s2 = S2;
test2(&s2);
}

12
src/test/ui/traits/trait-upcasting/type-checking-test-1.rs
View File

@ -9,12 +9,8 @@ trait Bar<T> {
}
fn test_specific(x: &dyn Foo) {
let _ = x as &dyn Bar<i32>; // FIXME: OK, eventually
//~^ ERROR non-primitive cast
//~^^ ERROR the trait bound `&dyn Foo: Bar<i32>` is not satisfied
let _ = x as &dyn Bar<u32>; // FIXME: OK, eventually
//~^ ERROR non-primitive cast
//~^^ ERROR the trait bound `&dyn Foo: Bar<u32>` is not satisfied
let _ = x as &dyn Bar<i32>; // OK
let _ = x as &dyn Bar<u32>; // OK
}
fn test_unknown_version(x: &dyn Foo) {
@ -24,9 +20,7 @@ fn test_unknown_version(x: &dyn Foo) {
}
fn test_infer_version(x: &dyn Foo) {
let a = x as &dyn Bar<_>; // FIXME: OK, eventually
//~^ ERROR non-primitive cast
//~^^ ERROR the trait bound `&dyn Foo: Bar<u32>` is not satisfied
let a = x as &dyn Bar<_>; // OK
let _: Option<u32> = a.bar();
}

63
src/test/ui/traits/trait-upcasting/type-checking-test-1.stderr
View File

@ -1,43 +1,5 @@
error[E0605]: non-primitive cast: `&dyn Foo` as `&dyn Bar<i32>`
--> $DIR/type-checking-test-1.rs:12:13
|
LL | let _ = x as &dyn Bar<i32>; // FIXME: OK, eventually
| ^^^^^^^^^^^^^^^^^^ invalid cast
|
help: consider borrowing the value
|
LL | let _ = &x as &dyn Bar<i32>; // FIXME: OK, eventually
| +
error[E0605]: non-primitive cast: `&dyn Foo` as `&dyn Bar<u32>`
--> $DIR/type-checking-test-1.rs:15:13
|
LL | let _ = x as &dyn Bar<u32>; // FIXME: OK, eventually
| ^^^^^^^^^^^^^^^^^^ invalid cast
|
help: consider borrowing the value
|
LL | let _ = &x as &dyn Bar<u32>; // FIXME: OK, eventually
| +
error[E0277]: the trait bound `&dyn Foo: Bar<i32>` is not satisfied
--> $DIR/type-checking-test-1.rs:12:13
|
LL | let _ = x as &dyn Bar<i32>; // FIXME: OK, eventually
| ^ the trait `Bar<i32>` is not implemented for `&dyn Foo`
|
= note: required for the cast to the object type `dyn Bar<i32>`
error[E0277]: the trait bound `&dyn Foo: Bar<u32>` is not satisfied
--> $DIR/type-checking-test-1.rs:15:13
|
LL | let _ = x as &dyn Bar<u32>; // FIXME: OK, eventually
| ^ the trait `Bar<u32>` is not implemented for `&dyn Foo`
|
= note: required for the cast to the object type `dyn Bar<u32>`
error[E0605]: non-primitive cast: `&dyn Foo` as `&dyn Bar<_>`
--> $DIR/type-checking-test-1.rs:21:13
--> $DIR/type-checking-test-1.rs:17:13
|
LL | let _ = x as &dyn Bar<_>; // Ambiguous
| ^^^^^^^^^^^^^^^^ invalid cast
@ -48,33 +10,14 @@ LL | let _ = &x as &dyn Bar<_>; // Ambiguous
| +
error[E0277]: the trait bound `&dyn Foo: Bar<_>` is not satisfied
--> $DIR/type-checking-test-1.rs:21:13
--> $DIR/type-checking-test-1.rs:17:13
|
LL | let _ = x as &dyn Bar<_>; // Ambiguous
| ^ the trait `Bar<_>` is not implemented for `&dyn Foo`
|
= note: required for the cast to the object type `dyn Bar<_>`
error[E0605]: non-primitive cast: `&dyn Foo` as `&dyn Bar<u32>`
--> $DIR/type-checking-test-1.rs:27:13
|
LL | let a = x as &dyn Bar<_>; // FIXME: OK, eventually
| ^^^^^^^^^^^^^^^^ invalid cast
|
help: consider borrowing the value
|
LL | let a = &x as &dyn Bar<_>; // FIXME: OK, eventually
| +
error[E0277]: the trait bound `&dyn Foo: Bar<u32>` is not satisfied
--> $DIR/type-checking-test-1.rs:27:13
|
LL | let a = x as &dyn Bar<_>; // FIXME: OK, eventually
| ^ the trait `Bar<u32>` is not implemented for `&dyn Foo`
|
= note: required for the cast to the object type `dyn Bar<u32>`
error: aborting due to 8 previous errors
error: aborting due to 2 previous errors
Some errors have detailed explanations: E0277, E0605.
For more information about an error, try `rustc --explain E0277`.

4
src/test/ui/traits/trait-upcasting/type-checking-test-2.rs
View File

@ -13,9 +13,7 @@ fn test_specific(x: &dyn Foo<i32>) {
}
fn test_specific2(x: &dyn Foo<u32>) {
let _ = x as &dyn Bar<i32>; // FIXME: OK, eventually
//~^ ERROR non-primitive cast
//~^^ ERROR the trait bound `&dyn Foo<u32>: Bar<i32>` is not satisfied
let _ = x as &dyn Bar<i32>; // OK
}
fn test_specific3(x: &dyn Foo<i32>) {

29
src/test/ui/traits/trait-upcasting/type-checking-test-2.stderr
View File

@ -1,24 +1,5 @@
error[E0605]: non-primitive cast: `&dyn Foo<u32>` as `&dyn Bar<i32>`
--> $DIR/type-checking-test-2.rs:16:13
|
LL | let _ = x as &dyn Bar<i32>; // FIXME: OK, eventually
| ^^^^^^^^^^^^^^^^^^ invalid cast
|
help: consider borrowing the value
|
LL | let _ = &x as &dyn Bar<i32>; // FIXME: OK, eventually
| +
error[E0277]: the trait bound `&dyn Foo<u32>: Bar<i32>` is not satisfied
--> $DIR/type-checking-test-2.rs:16:13
|
LL | let _ = x as &dyn Bar<i32>; // FIXME: OK, eventually
| ^ the trait `Bar<i32>` is not implemented for `&dyn Foo<u32>`
|
= note: required for the cast to the object type `dyn Bar<i32>`
error[E0605]: non-primitive cast: `&dyn Foo<i32>` as `&dyn Bar<u32>`
--> $DIR/type-checking-test-2.rs:22:13
--> $DIR/type-checking-test-2.rs:20:13
|
LL | let _ = x as &dyn Bar<u32>; // Error
| ^^^^^^^^^^^^^^^^^^ invalid cast
@ -29,7 +10,7 @@ LL | let _ = &x as &dyn Bar<u32>; // Error
| +
error[E0277]: the trait bound `&dyn Foo<i32>: Bar<u32>` is not satisfied
--> $DIR/type-checking-test-2.rs:22:13
--> $DIR/type-checking-test-2.rs:20:13
|
LL | let _ = x as &dyn Bar<u32>; // Error
| ^ the trait `Bar<u32>` is not implemented for `&dyn Foo<i32>`
@ -37,7 +18,7 @@ LL | let _ = x as &dyn Bar<u32>; // Error
= note: required for the cast to the object type `dyn Bar<u32>`
error[E0605]: non-primitive cast: `&dyn Foo<u32>` as `&dyn Bar<_>`
--> $DIR/type-checking-test-2.rs:28:13
--> $DIR/type-checking-test-2.rs:26:13
|
LL | let a = x as &dyn Bar<_>; // Ambiguous
| ^^^^^^^^^^^^^^^^ invalid cast
@ -48,14 +29,14 @@ LL | let a = &x as &dyn Bar<_>; // Ambiguous
| +
error[E0277]: the trait bound `&dyn Foo<u32>: Bar<_>` is not satisfied
--> $DIR/type-checking-test-2.rs:28:13
--> $DIR/type-checking-test-2.rs:26:13
|
LL | let a = x as &dyn Bar<_>; // Ambiguous
| ^ the trait `Bar<_>` is not implemented for `&dyn Foo<u32>`
|
= note: required for the cast to the object type `dyn Bar<_>`
error: aborting due to 6 previous errors
error: aborting due to 4 previous errors
Some errors have detailed explanations: E0277, E0605.
For more information about an error, try `rustc --explain E0277`.