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7086dd83cc
The initial naming of "Abi" was an awful mistake, conveying wrong ideas about how psABIs worked and even more about what the enum meant. It was only meant to represent the way the value would be described to a codegen backend as it was lowered to that intermediate representation. It was never meant to mean anything about the actual psABI handling! The conflation is because LLVM typically will associate a certain form with a certain ABI, but even that does not hold when the special cases that actually exist arise, plus the IR annotations that modify the ABI. Reframe `rustc_abi::Abi` as the `BackendRepr` of the type, and rename `BackendRepr::Aggregate` as `BackendRepr::Memory`. Unfortunately, due to the persistent misunderstandings, this too is now incorrect: - Scattered ABI-relevant code is entangled with BackendRepr - We do not always pre-compute a correct BackendRepr that reflects how we "actually" want this value to be handled, so we leave the backend interface to also inject various special-cases here - In some cases `BackendRepr::Memory` is a "real" aggregate, but in others it is in fact using memory, and in some cases it is a scalar! Our rustc-to-backend lowering code handles this sort of thing right now. That will eventually be addressed by lifting duplicated lowering code to either rustc_codegen_ssa or rustc_target as appropriate.
935 lines
36 KiB
Rust
935 lines
36 KiB
Rust
//! "Dyn-compatibility"[^1] refers to the ability for a trait to be converted
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//! to a trait object. In general, traits may only be converted to a trait
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//! object if certain criteria are met.
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//!
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//! [^1]: Formerly known as "object safety".
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use std::iter;
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use std::ops::ControlFlow;
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use rustc_errors::FatalError;
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use rustc_hir as hir;
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use rustc_hir::def_id::DefId;
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use rustc_middle::query::Providers;
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use rustc_middle::ty::{
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self, EarlyBinder, ExistentialPredicateStableCmpExt as _, GenericArgs, Ty, TyCtxt,
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TypeFoldable, TypeFolder, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable,
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TypeVisitableExt, TypeVisitor, Upcast,
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};
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use rustc_span::Span;
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use rustc_span::symbol::Symbol;
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use rustc_target::abi::BackendRepr;
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use smallvec::SmallVec;
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use tracing::{debug, instrument};
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use super::elaborate;
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use crate::infer::TyCtxtInferExt;
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pub use crate::traits::DynCompatibilityViolation;
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use crate::traits::query::evaluate_obligation::InferCtxtExt;
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use crate::traits::{MethodViolationCode, Obligation, ObligationCause, util};
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/// Returns the dyn-compatibility violations that affect HIR ty lowering.
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///
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/// Currently that is `Self` in supertraits. This is needed
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/// because `dyn_compatibility_violations` can't be used during
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/// type collection.
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#[instrument(level = "debug", skip(tcx), ret)]
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pub fn hir_ty_lowering_dyn_compatibility_violations(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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) -> Vec<DynCompatibilityViolation> {
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debug_assert!(tcx.generics_of(trait_def_id).has_self);
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tcx.supertrait_def_ids(trait_def_id)
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.map(|def_id| predicates_reference_self(tcx, def_id, true))
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.filter(|spans| !spans.is_empty())
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.map(DynCompatibilityViolation::SupertraitSelf)
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.collect()
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}
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fn dyn_compatibility_violations(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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) -> &'_ [DynCompatibilityViolation] {
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debug_assert!(tcx.generics_of(trait_def_id).has_self);
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debug!("dyn_compatibility_violations: {:?}", trait_def_id);
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tcx.arena.alloc_from_iter(
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tcx.supertrait_def_ids(trait_def_id)
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.flat_map(|def_id| dyn_compatibility_violations_for_trait(tcx, def_id)),
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)
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}
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fn is_dyn_compatible(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
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tcx.dyn_compatibility_violations(trait_def_id).is_empty()
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}
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/// We say a method is *vtable safe* if it can be invoked on a trait
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/// object. Note that object-safe traits can have some
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/// non-vtable-safe methods, so long as they require `Self: Sized` or
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/// otherwise ensure that they cannot be used when `Self = Trait`.
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pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: ty::AssocItem) -> bool {
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debug_assert!(tcx.generics_of(trait_def_id).has_self);
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debug!("is_vtable_safe_method({:?}, {:?})", trait_def_id, method);
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// Any method that has a `Self: Sized` bound cannot be called.
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if tcx.generics_require_sized_self(method.def_id) {
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return false;
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}
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virtual_call_violations_for_method(tcx, trait_def_id, method).is_empty()
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}
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#[instrument(level = "debug", skip(tcx), ret)]
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fn dyn_compatibility_violations_for_trait(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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) -> Vec<DynCompatibilityViolation> {
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// Check assoc items for violations.
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let mut violations: Vec<_> = tcx
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.associated_items(trait_def_id)
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.in_definition_order()
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.flat_map(|&item| dyn_compatibility_violations_for_assoc_item(tcx, trait_def_id, item))
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.collect();
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// Check the trait itself.
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if trait_has_sized_self(tcx, trait_def_id) {
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// We don't want to include the requirement from `Sized` itself to be `Sized` in the list.
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let spans = get_sized_bounds(tcx, trait_def_id);
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violations.push(DynCompatibilityViolation::SizedSelf(spans));
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}
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let spans = predicates_reference_self(tcx, trait_def_id, false);
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if !spans.is_empty() {
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violations.push(DynCompatibilityViolation::SupertraitSelf(spans));
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}
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let spans = bounds_reference_self(tcx, trait_def_id);
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if !spans.is_empty() {
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violations.push(DynCompatibilityViolation::SupertraitSelf(spans));
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}
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let spans = super_predicates_have_non_lifetime_binders(tcx, trait_def_id);
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if !spans.is_empty() {
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violations.push(DynCompatibilityViolation::SupertraitNonLifetimeBinder(spans));
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}
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if violations.is_empty() {
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for item in tcx.associated_items(trait_def_id).in_definition_order() {
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if let ty::AssocKind::Fn = item.kind {
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check_receiver_correct(tcx, trait_def_id, *item);
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}
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}
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}
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violations
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}
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fn sized_trait_bound_spans<'tcx>(
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tcx: TyCtxt<'tcx>,
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bounds: hir::GenericBounds<'tcx>,
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) -> impl 'tcx + Iterator<Item = Span> {
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bounds.iter().filter_map(move |b| match b {
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hir::GenericBound::Trait(trait_ref)
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if trait_has_sized_self(
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tcx,
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trait_ref.trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
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) =>
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{
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// Fetch spans for supertraits that are `Sized`: `trait T: Super`
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Some(trait_ref.span)
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}
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_ => None,
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})
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}
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fn get_sized_bounds(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span; 1]> {
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tcx.hir()
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.get_if_local(trait_def_id)
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.and_then(|node| match node {
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hir::Node::Item(hir::Item {
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kind: hir::ItemKind::Trait(.., generics, bounds, _),
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..
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}) => Some(
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generics
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.predicates
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.iter()
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.filter_map(|pred| {
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match pred {
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hir::WherePredicate::BoundPredicate(pred)
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if pred.bounded_ty.hir_id.owner.to_def_id() == trait_def_id =>
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{
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// Fetch spans for trait bounds that are Sized:
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// `trait T where Self: Pred`
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Some(sized_trait_bound_spans(tcx, pred.bounds))
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}
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_ => None,
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}
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})
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.flatten()
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// Fetch spans for supertraits that are `Sized`: `trait T: Super`.
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.chain(sized_trait_bound_spans(tcx, bounds))
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.collect::<SmallVec<[Span; 1]>>(),
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),
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_ => None,
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})
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.unwrap_or_else(SmallVec::new)
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}
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fn predicates_reference_self(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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supertraits_only: bool,
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) -> SmallVec<[Span; 1]> {
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let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_def_id));
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let predicates = if supertraits_only {
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tcx.explicit_super_predicates_of(trait_def_id).skip_binder()
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} else {
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tcx.predicates_of(trait_def_id).predicates
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};
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predicates
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.iter()
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.map(|&(predicate, sp)| (predicate.instantiate_supertrait(tcx, trait_ref), sp))
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.filter_map(|(clause, sp)| {
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// Super predicates cannot allow self projections, since they're
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// impossible to make into existential bounds without eager resolution
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// or something.
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// e.g. `trait A: B<Item = Self::Assoc>`.
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predicate_references_self(tcx, trait_def_id, clause, sp, AllowSelfProjections::No)
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})
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.collect()
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}
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fn bounds_reference_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span; 1]> {
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tcx.associated_items(trait_def_id)
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.in_definition_order()
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.filter(|item| item.kind == ty::AssocKind::Type)
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.flat_map(|item| tcx.explicit_item_bounds(item.def_id).iter_identity_copied())
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.filter_map(|(clause, sp)| {
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// Item bounds *can* have self projections, since they never get
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// their self type erased.
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predicate_references_self(tcx, trait_def_id, clause, sp, AllowSelfProjections::Yes)
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})
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.collect()
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}
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fn predicate_references_self<'tcx>(
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tcx: TyCtxt<'tcx>,
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trait_def_id: DefId,
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predicate: ty::Clause<'tcx>,
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sp: Span,
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allow_self_projections: AllowSelfProjections,
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) -> Option<Span> {
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match predicate.kind().skip_binder() {
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ty::ClauseKind::Trait(ref data) => {
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// In the case of a trait predicate, we can skip the "self" type.
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data.trait_ref.args[1..].iter().any(|&arg| contains_illegal_self_type_reference(tcx, trait_def_id, arg, allow_self_projections)).then_some(sp)
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}
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ty::ClauseKind::Projection(ref data) => {
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// And similarly for projections. This should be redundant with
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// the previous check because any projection should have a
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// matching `Trait` predicate with the same inputs, but we do
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// the check to be safe.
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//
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// It's also won't be redundant if we allow type-generic associated
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// types for trait objects.
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//
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// Note that we *do* allow projection *outputs* to contain
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// `self` (i.e., `trait Foo: Bar<Output=Self::Result> { type Result; }`),
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// we just require the user to specify *both* outputs
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// in the object type (i.e., `dyn Foo<Output=(), Result=()>`).
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//
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// This is ALT2 in issue #56288, see that for discussion of the
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// possible alternatives.
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data.projection_term.args[1..].iter().any(|&arg| contains_illegal_self_type_reference(tcx, trait_def_id, arg, allow_self_projections)).then_some(sp)
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}
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ty::ClauseKind::ConstArgHasType(_ct, ty) => contains_illegal_self_type_reference(tcx, trait_def_id, ty, allow_self_projections).then_some(sp),
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ty::ClauseKind::WellFormed(..)
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| ty::ClauseKind::TypeOutlives(..)
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| ty::ClauseKind::RegionOutlives(..)
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// FIXME(generic_const_exprs): this can mention `Self`
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| ty::ClauseKind::ConstEvaluatable(..)
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| ty::ClauseKind::HostEffect(..)
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=> None,
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}
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}
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fn super_predicates_have_non_lifetime_binders(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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) -> SmallVec<[Span; 1]> {
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// If non_lifetime_binders is disabled, then exit early
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if !tcx.features().non_lifetime_binders() {
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return SmallVec::new();
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}
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tcx.explicit_super_predicates_of(trait_def_id)
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.iter_identity_copied()
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.filter_map(|(pred, span)| pred.has_non_region_bound_vars().then_some(span))
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.collect()
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}
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fn trait_has_sized_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
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tcx.generics_require_sized_self(trait_def_id)
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}
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fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
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let Some(sized_def_id) = tcx.lang_items().sized_trait() else {
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return false; /* No Sized trait, can't require it! */
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};
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// Search for a predicate like `Self : Sized` amongst the trait bounds.
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let predicates = tcx.predicates_of(def_id);
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let predicates = predicates.instantiate_identity(tcx).predicates;
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elaborate(tcx, predicates).any(|pred| match pred.kind().skip_binder() {
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ty::ClauseKind::Trait(ref trait_pred) => {
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trait_pred.def_id() == sized_def_id && trait_pred.self_ty().is_param(0)
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}
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ty::ClauseKind::RegionOutlives(_)
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| ty::ClauseKind::TypeOutlives(_)
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| ty::ClauseKind::Projection(_)
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| ty::ClauseKind::ConstArgHasType(_, _)
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| ty::ClauseKind::WellFormed(_)
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| ty::ClauseKind::ConstEvaluatable(_)
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| ty::ClauseKind::HostEffect(..) => false,
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})
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}
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/// Returns `Some(_)` if this item makes the containing trait dyn-incompatible.
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#[instrument(level = "debug", skip(tcx), ret)]
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pub fn dyn_compatibility_violations_for_assoc_item(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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item: ty::AssocItem,
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) -> Vec<DynCompatibilityViolation> {
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// Any item that has a `Self : Sized` requisite is otherwise
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// exempt from the regulations.
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if tcx.generics_require_sized_self(item.def_id) {
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return Vec::new();
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}
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match item.kind {
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// Associated consts are never dyn-compatible, as they can't have `where` bounds yet at all,
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// and associated const bounds in trait objects aren't a thing yet either.
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ty::AssocKind::Const => {
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vec![DynCompatibilityViolation::AssocConst(item.name, item.ident(tcx).span)]
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}
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ty::AssocKind::Fn => virtual_call_violations_for_method(tcx, trait_def_id, item)
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.into_iter()
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.map(|v| {
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let node = tcx.hir().get_if_local(item.def_id);
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// Get an accurate span depending on the violation.
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let span = match (&v, node) {
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(MethodViolationCode::ReferencesSelfInput(Some(span)), _) => *span,
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(MethodViolationCode::UndispatchableReceiver(Some(span)), _) => *span,
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(MethodViolationCode::ReferencesImplTraitInTrait(span), _) => *span,
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(MethodViolationCode::ReferencesSelfOutput, Some(node)) => {
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node.fn_decl().map_or(item.ident(tcx).span, |decl| decl.output.span())
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}
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_ => item.ident(tcx).span,
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};
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DynCompatibilityViolation::Method(item.name, v, span)
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})
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.collect(),
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// Associated types can only be dyn-compatible if they have `Self: Sized` bounds.
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ty::AssocKind::Type => {
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if !tcx.features().generic_associated_types_extended()
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&& !tcx.generics_of(item.def_id).is_own_empty()
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&& !item.is_impl_trait_in_trait()
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{
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vec![DynCompatibilityViolation::GAT(item.name, item.ident(tcx).span)]
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} else {
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// We will permit associated types if they are explicitly mentioned in the trait object.
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// We can't check this here, as here we only check if it is guaranteed to not be possible.
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Vec::new()
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}
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}
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}
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}
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/// Returns `Some(_)` if this method cannot be called on a trait
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/// object; this does not necessarily imply that the enclosing trait
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/// is dyn-incompatible, because the method might have a where clause
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/// `Self: Sized`.
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fn virtual_call_violations_for_method<'tcx>(
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tcx: TyCtxt<'tcx>,
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trait_def_id: DefId,
|
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method: ty::AssocItem,
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) -> Vec<MethodViolationCode> {
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let sig = tcx.fn_sig(method.def_id).instantiate_identity();
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|
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// The method's first parameter must be named `self`
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if !method.fn_has_self_parameter {
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let sugg = if let Some(hir::Node::TraitItem(hir::TraitItem {
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generics,
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kind: hir::TraitItemKind::Fn(sig, _),
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..
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})) = tcx.hir().get_if_local(method.def_id).as_ref()
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{
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let sm = tcx.sess.source_map();
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Some((
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(
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format!("&self{}", if sig.decl.inputs.is_empty() { "" } else { ", " }),
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sm.span_through_char(sig.span, '(').shrink_to_hi(),
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),
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(
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format!("{} Self: Sized", generics.add_where_or_trailing_comma()),
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generics.tail_span_for_predicate_suggestion(),
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),
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))
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} else {
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None
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};
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|
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// Not having `self` parameter messes up the later checks,
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// so we need to return instead of pushing
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return vec![MethodViolationCode::StaticMethod(sugg)];
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}
|
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|
|
let mut errors = Vec::new();
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|
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for (i, &input_ty) in sig.skip_binder().inputs().iter().enumerate().skip(1) {
|
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if contains_illegal_self_type_reference(
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tcx,
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trait_def_id,
|
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sig.rebind(input_ty),
|
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AllowSelfProjections::Yes,
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) {
|
|
let span = if let Some(hir::Node::TraitItem(hir::TraitItem {
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|
kind: hir::TraitItemKind::Fn(sig, _),
|
|
..
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|
})) = tcx.hir().get_if_local(method.def_id).as_ref()
|
|
{
|
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Some(sig.decl.inputs[i].span)
|
|
} else {
|
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None
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|
};
|
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errors.push(MethodViolationCode::ReferencesSelfInput(span));
|
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}
|
|
}
|
|
if contains_illegal_self_type_reference(
|
|
tcx,
|
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trait_def_id,
|
|
sig.output(),
|
|
AllowSelfProjections::Yes,
|
|
) {
|
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errors.push(MethodViolationCode::ReferencesSelfOutput);
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|
}
|
|
if let Some(code) = contains_illegal_impl_trait_in_trait(tcx, method.def_id, sig.output()) {
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|
errors.push(code);
|
|
}
|
|
|
|
// We can't monomorphize things like `fn foo<A>(...)`.
|
|
let own_counts = tcx.generics_of(method.def_id).own_counts();
|
|
if own_counts.types > 0 || own_counts.consts > 0 {
|
|
errors.push(MethodViolationCode::Generic);
|
|
}
|
|
|
|
let receiver_ty = tcx.liberate_late_bound_regions(method.def_id, sig.input(0));
|
|
|
|
// Until `unsized_locals` is fully implemented, `self: Self` can't be dispatched on.
|
|
// However, this is already considered object-safe. We allow it as a special case here.
|
|
// FIXME(mikeyhew) get rid of this `if` statement once `receiver_is_dispatchable` allows
|
|
// `Receiver: Unsize<Receiver[Self => dyn Trait]>`.
|
|
if receiver_ty != tcx.types.self_param {
|
|
if !receiver_is_dispatchable(tcx, method, receiver_ty) {
|
|
let span = if let Some(hir::Node::TraitItem(hir::TraitItem {
|
|
kind: hir::TraitItemKind::Fn(sig, _),
|
|
..
|
|
})) = tcx.hir().get_if_local(method.def_id).as_ref()
|
|
{
|
|
Some(sig.decl.inputs[0].span)
|
|
} else {
|
|
None
|
|
};
|
|
errors.push(MethodViolationCode::UndispatchableReceiver(span));
|
|
} else {
|
|
// We confirm that the `receiver_is_dispatchable` is accurate later,
|
|
// see `check_receiver_correct`. It should be kept in sync with this code.
|
|
}
|
|
}
|
|
|
|
// NOTE: This check happens last, because it results in a lint, and not a
|
|
// hard error.
|
|
if tcx.predicates_of(method.def_id).predicates.iter().any(|&(pred, _span)| {
|
|
// dyn Trait is okay:
|
|
//
|
|
// trait Trait {
|
|
// fn f(&self) where Self: 'static;
|
|
// }
|
|
//
|
|
// because a trait object can't claim to live longer than the concrete
|
|
// type. If the lifetime bound holds on dyn Trait then it's guaranteed
|
|
// to hold as well on the concrete type.
|
|
if pred.as_type_outlives_clause().is_some() {
|
|
return false;
|
|
}
|
|
|
|
// dyn Trait is okay:
|
|
//
|
|
// auto trait AutoTrait {}
|
|
//
|
|
// trait Trait {
|
|
// fn f(&self) where Self: AutoTrait;
|
|
// }
|
|
//
|
|
// because `impl AutoTrait for dyn Trait` is disallowed by coherence.
|
|
// Traits with a default impl are implemented for a trait object if and
|
|
// only if the autotrait is one of the trait object's trait bounds, like
|
|
// in `dyn Trait + AutoTrait`. This guarantees that trait objects only
|
|
// implement auto traits if the underlying type does as well.
|
|
if let ty::ClauseKind::Trait(ty::TraitPredicate {
|
|
trait_ref: pred_trait_ref,
|
|
polarity: ty::PredicatePolarity::Positive,
|
|
}) = pred.kind().skip_binder()
|
|
&& pred_trait_ref.self_ty() == tcx.types.self_param
|
|
&& tcx.trait_is_auto(pred_trait_ref.def_id)
|
|
{
|
|
// Consider bounds like `Self: Bound<Self>`. Auto traits are not
|
|
// allowed to have generic parameters so `auto trait Bound<T> {}`
|
|
// would already have reported an error at the definition of the
|
|
// auto trait.
|
|
if pred_trait_ref.args.len() != 1 {
|
|
assert!(
|
|
tcx.dcx().has_errors().is_some(),
|
|
"auto traits cannot have generic parameters"
|
|
);
|
|
}
|
|
return false;
|
|
}
|
|
|
|
contains_illegal_self_type_reference(tcx, trait_def_id, pred, AllowSelfProjections::Yes)
|
|
}) {
|
|
errors.push(MethodViolationCode::WhereClauseReferencesSelf);
|
|
}
|
|
|
|
errors
|
|
}
|
|
|
|
/// This code checks that `receiver_is_dispatchable` is correctly implemented.
|
|
///
|
|
/// This check is outlined from the dyn-compatibility check to avoid cycles with
|
|
/// layout computation, which relies on knowing whether methods are dyn-compatible.
|
|
fn check_receiver_correct<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId, method: ty::AssocItem) {
|
|
if !is_vtable_safe_method(tcx, trait_def_id, method) {
|
|
return;
|
|
}
|
|
|
|
let method_def_id = method.def_id;
|
|
let sig = tcx.fn_sig(method_def_id).instantiate_identity();
|
|
let param_env = tcx.param_env(method_def_id);
|
|
let receiver_ty = tcx.liberate_late_bound_regions(method_def_id, sig.input(0));
|
|
|
|
if receiver_ty == tcx.types.self_param {
|
|
// Assumed OK, may change later if unsized_locals permits `self: Self` as dispatchable.
|
|
return;
|
|
}
|
|
|
|
// e.g., `Rc<()>`
|
|
let unit_receiver_ty = receiver_for_self_ty(tcx, receiver_ty, tcx.types.unit, method_def_id);
|
|
match tcx.layout_of(param_env.and(unit_receiver_ty)).map(|l| l.backend_repr) {
|
|
Ok(BackendRepr::Scalar(..)) => (),
|
|
abi => {
|
|
tcx.dcx().span_delayed_bug(
|
|
tcx.def_span(method_def_id),
|
|
format!("receiver {unit_receiver_ty:?} when `Self = ()` should have a Scalar ABI; found {abi:?}"),
|
|
);
|
|
}
|
|
}
|
|
|
|
let trait_object_ty = object_ty_for_trait(tcx, trait_def_id, tcx.lifetimes.re_static);
|
|
|
|
// e.g., `Rc<dyn Trait>`
|
|
let trait_object_receiver =
|
|
receiver_for_self_ty(tcx, receiver_ty, trait_object_ty, method_def_id);
|
|
match tcx.layout_of(param_env.and(trait_object_receiver)).map(|l| l.backend_repr) {
|
|
Ok(BackendRepr::ScalarPair(..)) => (),
|
|
abi => {
|
|
tcx.dcx().span_delayed_bug(
|
|
tcx.def_span(method_def_id),
|
|
format!(
|
|
"receiver {trait_object_receiver:?} when `Self = {trait_object_ty}` should have a ScalarPair ABI; found {abi:?}"
|
|
),
|
|
);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Performs a type instantiation to produce the version of `receiver_ty` when `Self = self_ty`.
|
|
/// For example, for `receiver_ty = Rc<Self>` and `self_ty = Foo`, returns `Rc<Foo>`.
|
|
fn receiver_for_self_ty<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
receiver_ty: Ty<'tcx>,
|
|
self_ty: Ty<'tcx>,
|
|
method_def_id: DefId,
|
|
) -> Ty<'tcx> {
|
|
debug!("receiver_for_self_ty({:?}, {:?}, {:?})", receiver_ty, self_ty, method_def_id);
|
|
let args = GenericArgs::for_item(tcx, method_def_id, |param, _| {
|
|
if param.index == 0 { self_ty.into() } else { tcx.mk_param_from_def(param) }
|
|
});
|
|
|
|
let result = EarlyBinder::bind(receiver_ty).instantiate(tcx, args);
|
|
debug!(
|
|
"receiver_for_self_ty({:?}, {:?}, {:?}) = {:?}",
|
|
receiver_ty, self_ty, method_def_id, result
|
|
);
|
|
result
|
|
}
|
|
|
|
/// Creates the object type for the current trait. For example,
|
|
/// if the current trait is `Deref`, then this will be
|
|
/// `dyn Deref<Target = Self::Target> + 'static`.
|
|
#[instrument(level = "trace", skip(tcx), ret)]
|
|
fn object_ty_for_trait<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
trait_def_id: DefId,
|
|
lifetime: ty::Region<'tcx>,
|
|
) -> Ty<'tcx> {
|
|
let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
|
|
debug!(?trait_ref);
|
|
|
|
let trait_predicate = ty::Binder::dummy(ty::ExistentialPredicate::Trait(
|
|
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref),
|
|
));
|
|
debug!(?trait_predicate);
|
|
|
|
let pred: ty::Predicate<'tcx> = trait_ref.upcast(tcx);
|
|
let mut elaborated_predicates: Vec<_> = elaborate(tcx, [pred])
|
|
.filter_map(|pred| {
|
|
debug!(?pred);
|
|
let pred = pred.as_projection_clause()?;
|
|
Some(pred.map_bound(|p| {
|
|
ty::ExistentialPredicate::Projection(ty::ExistentialProjection::erase_self_ty(
|
|
tcx, p,
|
|
))
|
|
}))
|
|
})
|
|
.collect();
|
|
// NOTE: Since #37965, the existential predicates list has depended on the
|
|
// list of predicates to be sorted. This is mostly to enforce that the primary
|
|
// predicate comes first.
|
|
elaborated_predicates.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
|
|
elaborated_predicates.dedup();
|
|
|
|
let existential_predicates = tcx.mk_poly_existential_predicates_from_iter(
|
|
iter::once(trait_predicate).chain(elaborated_predicates),
|
|
);
|
|
debug!(?existential_predicates);
|
|
|
|
Ty::new_dynamic(tcx, existential_predicates, lifetime, ty::Dyn)
|
|
}
|
|
|
|
/// Checks the method's receiver (the `self` argument) can be dispatched on when `Self` is a
|
|
/// trait object. We require that `DispatchableFromDyn` be implemented for the receiver type
|
|
/// in the following way:
|
|
/// - let `Receiver` be the type of the `self` argument, i.e `Self`, `&Self`, `Rc<Self>`,
|
|
/// - require the following bound:
|
|
///
|
|
/// ```ignore (not-rust)
|
|
/// Receiver[Self => T]: DispatchFromDyn<Receiver[Self => dyn Trait]>
|
|
/// ```
|
|
///
|
|
/// where `Foo[X => Y]` means "the same type as `Foo`, but with `X` replaced with `Y`"
|
|
/// (instantiation notation).
|
|
///
|
|
/// Some examples of receiver types and their required obligation:
|
|
/// - `&'a mut self` requires `&'a mut Self: DispatchFromDyn<&'a mut dyn Trait>`,
|
|
/// - `self: Rc<Self>` requires `Rc<Self>: DispatchFromDyn<Rc<dyn Trait>>`,
|
|
/// - `self: Pin<Box<Self>>` requires `Pin<Box<Self>>: DispatchFromDyn<Pin<Box<dyn Trait>>>`.
|
|
///
|
|
/// The only case where the receiver is not dispatchable, but is still a valid receiver
|
|
/// type (just not object-safe), is when there is more than one level of pointer indirection.
|
|
/// E.g., `self: &&Self`, `self: &Rc<Self>`, `self: Box<Box<Self>>`. In these cases, there
|
|
/// is no way, or at least no inexpensive way, to coerce the receiver from the version where
|
|
/// `Self = dyn Trait` to the version where `Self = T`, where `T` is the unknown erased type
|
|
/// contained by the trait object, because the object that needs to be coerced is behind
|
|
/// a pointer.
|
|
///
|
|
/// In practice, we cannot use `dyn Trait` explicitly in the obligation because it would result in
|
|
/// a new check that `Trait` is dyn-compatible, creating a cycle (until dyn_compatible_for_dispatch
|
|
/// is stabilized, see tracking issue <https://github.com/rust-lang/rust/issues/43561>).
|
|
/// Instead, we fudge a little by introducing a new type parameter `U` such that
|
|
/// `Self: Unsize<U>` and `U: Trait + ?Sized`, and use `U` in place of `dyn Trait`.
|
|
/// Written as a chalk-style query:
|
|
/// ```ignore (not-rust)
|
|
/// forall (U: Trait + ?Sized) {
|
|
/// if (Self: Unsize<U>) {
|
|
/// Receiver: DispatchFromDyn<Receiver[Self => U]>
|
|
/// }
|
|
/// }
|
|
/// ```
|
|
/// for `self: &'a mut Self`, this means `&'a mut Self: DispatchFromDyn<&'a mut U>`
|
|
/// for `self: Rc<Self>`, this means `Rc<Self>: DispatchFromDyn<Rc<U>>`
|
|
/// for `self: Pin<Box<Self>>`, this means `Pin<Box<Self>>: DispatchFromDyn<Pin<Box<U>>>`
|
|
//
|
|
// FIXME(mikeyhew) when unsized receivers are implemented as part of unsized rvalues, add this
|
|
// fallback query: `Receiver: Unsize<Receiver[Self => U]>` to support receivers like
|
|
// `self: Wrapper<Self>`.
|
|
fn receiver_is_dispatchable<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
method: ty::AssocItem,
|
|
receiver_ty: Ty<'tcx>,
|
|
) -> bool {
|
|
debug!("receiver_is_dispatchable: method = {:?}, receiver_ty = {:?}", method, receiver_ty);
|
|
|
|
let traits = (tcx.lang_items().unsize_trait(), tcx.lang_items().dispatch_from_dyn_trait());
|
|
let (Some(unsize_did), Some(dispatch_from_dyn_did)) = traits else {
|
|
debug!("receiver_is_dispatchable: Missing Unsize or DispatchFromDyn traits");
|
|
return false;
|
|
};
|
|
|
|
// the type `U` in the query
|
|
// use a bogus type parameter to mimic a forall(U) query using u32::MAX for now.
|
|
// FIXME(mikeyhew) this is a total hack. Once dyn_compatible_for_dispatch is stabilized, we can
|
|
// replace this with `dyn Trait`
|
|
let unsized_self_ty: Ty<'tcx> =
|
|
Ty::new_param(tcx, u32::MAX, Symbol::intern("RustaceansAreAwesome"));
|
|
|
|
// `Receiver[Self => U]`
|
|
let unsized_receiver_ty =
|
|
receiver_for_self_ty(tcx, receiver_ty, unsized_self_ty, method.def_id);
|
|
|
|
// create a modified param env, with `Self: Unsize<U>` and `U: Trait` added to caller bounds
|
|
// `U: ?Sized` is already implied here
|
|
let param_env = {
|
|
let param_env = tcx.param_env(method.def_id);
|
|
|
|
// Self: Unsize<U>
|
|
let unsize_predicate =
|
|
ty::TraitRef::new(tcx, unsize_did, [tcx.types.self_param, unsized_self_ty]).upcast(tcx);
|
|
|
|
// U: Trait<Arg1, ..., ArgN>
|
|
let trait_predicate = {
|
|
let trait_def_id = method.trait_container(tcx).unwrap();
|
|
let args = GenericArgs::for_item(tcx, trait_def_id, |param, _| {
|
|
if param.index == 0 { unsized_self_ty.into() } else { tcx.mk_param_from_def(param) }
|
|
});
|
|
|
|
ty::TraitRef::new_from_args(tcx, trait_def_id, args).upcast(tcx)
|
|
};
|
|
|
|
let caller_bounds =
|
|
param_env.caller_bounds().iter().chain([unsize_predicate, trait_predicate]);
|
|
|
|
ty::ParamEnv::new(tcx.mk_clauses_from_iter(caller_bounds), param_env.reveal())
|
|
};
|
|
|
|
// Receiver: DispatchFromDyn<Receiver[Self => U]>
|
|
let obligation = {
|
|
let predicate =
|
|
ty::TraitRef::new(tcx, dispatch_from_dyn_did, [receiver_ty, unsized_receiver_ty]);
|
|
|
|
Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate)
|
|
};
|
|
|
|
let infcx = tcx.infer_ctxt().build();
|
|
// the receiver is dispatchable iff the obligation holds
|
|
infcx.predicate_must_hold_modulo_regions(&obligation)
|
|
}
|
|
|
|
#[derive(Copy, Clone)]
|
|
enum AllowSelfProjections {
|
|
Yes,
|
|
No,
|
|
}
|
|
|
|
/// This is somewhat subtle. In general, we want to forbid
|
|
/// references to `Self` in the argument and return types,
|
|
/// since the value of `Self` is erased. However, there is one
|
|
/// exception: it is ok to reference `Self` in order to access
|
|
/// an associated type of the current trait, since we retain
|
|
/// the value of those associated types in the object type
|
|
/// itself.
|
|
///
|
|
/// ```rust,ignore (example)
|
|
/// trait SuperTrait {
|
|
/// type X;
|
|
/// }
|
|
///
|
|
/// trait Trait : SuperTrait {
|
|
/// type Y;
|
|
/// fn foo(&self, x: Self) // bad
|
|
/// fn foo(&self) -> Self // bad
|
|
/// fn foo(&self) -> Option<Self> // bad
|
|
/// fn foo(&self) -> Self::Y // OK, desugars to next example
|
|
/// fn foo(&self) -> <Self as Trait>::Y // OK
|
|
/// fn foo(&self) -> Self::X // OK, desugars to next example
|
|
/// fn foo(&self) -> <Self as SuperTrait>::X // OK
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// However, it is not as simple as allowing `Self` in a projected
|
|
/// type, because there are illegal ways to use `Self` as well:
|
|
///
|
|
/// ```rust,ignore (example)
|
|
/// trait Trait : SuperTrait {
|
|
/// ...
|
|
/// fn foo(&self) -> <Self as SomeOtherTrait>::X;
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Here we will not have the type of `X` recorded in the
|
|
/// object type, and we cannot resolve `Self as SomeOtherTrait`
|
|
/// without knowing what `Self` is.
|
|
fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<TyCtxt<'tcx>>>(
|
|
tcx: TyCtxt<'tcx>,
|
|
trait_def_id: DefId,
|
|
value: T,
|
|
allow_self_projections: AllowSelfProjections,
|
|
) -> bool {
|
|
value
|
|
.visit_with(&mut IllegalSelfTypeVisitor {
|
|
tcx,
|
|
trait_def_id,
|
|
supertraits: None,
|
|
allow_self_projections,
|
|
})
|
|
.is_break()
|
|
}
|
|
|
|
struct IllegalSelfTypeVisitor<'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
trait_def_id: DefId,
|
|
supertraits: Option<Vec<ty::TraitRef<'tcx>>>,
|
|
allow_self_projections: AllowSelfProjections,
|
|
}
|
|
|
|
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for IllegalSelfTypeVisitor<'tcx> {
|
|
type Result = ControlFlow<()>;
|
|
|
|
fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
|
|
match t.kind() {
|
|
ty::Param(_) => {
|
|
if t == self.tcx.types.self_param {
|
|
ControlFlow::Break(())
|
|
} else {
|
|
ControlFlow::Continue(())
|
|
}
|
|
}
|
|
ty::Alias(ty::Projection, ref data) if self.tcx.is_impl_trait_in_trait(data.def_id) => {
|
|
// We'll deny these later in their own pass
|
|
ControlFlow::Continue(())
|
|
}
|
|
ty::Alias(ty::Projection, ref data) => {
|
|
match self.allow_self_projections {
|
|
AllowSelfProjections::Yes => {
|
|
// This is a projected type `<Foo as SomeTrait>::X`.
|
|
|
|
// Compute supertraits of current trait lazily.
|
|
if self.supertraits.is_none() {
|
|
self.supertraits = Some(
|
|
util::supertraits(
|
|
self.tcx,
|
|
ty::Binder::dummy(ty::TraitRef::identity(
|
|
self.tcx,
|
|
self.trait_def_id,
|
|
)),
|
|
)
|
|
.map(|trait_ref| {
|
|
self.tcx.erase_regions(
|
|
self.tcx.instantiate_bound_regions_with_erased(trait_ref),
|
|
)
|
|
})
|
|
.collect(),
|
|
);
|
|
}
|
|
|
|
// Determine whether the trait reference `Foo as
|
|
// SomeTrait` is in fact a supertrait of the
|
|
// current trait. In that case, this type is
|
|
// legal, because the type `X` will be specified
|
|
// in the object type. Note that we can just use
|
|
// direct equality here because all of these types
|
|
// are part of the formal parameter listing, and
|
|
// hence there should be no inference variables.
|
|
let is_supertrait_of_current_trait =
|
|
self.supertraits.as_ref().unwrap().contains(
|
|
&data.trait_ref(self.tcx).fold_with(
|
|
&mut EraseEscapingBoundRegions {
|
|
tcx: self.tcx,
|
|
binder: ty::INNERMOST,
|
|
},
|
|
),
|
|
);
|
|
|
|
// only walk contained types if it's not a super trait
|
|
if is_supertrait_of_current_trait {
|
|
ControlFlow::Continue(())
|
|
} else {
|
|
t.super_visit_with(self) // POSSIBLY reporting an error
|
|
}
|
|
}
|
|
AllowSelfProjections::No => t.super_visit_with(self),
|
|
}
|
|
}
|
|
_ => t.super_visit_with(self),
|
|
}
|
|
}
|
|
|
|
fn visit_const(&mut self, ct: ty::Const<'tcx>) -> Self::Result {
|
|
// Constants can only influence dyn-compatibility if they are generic and reference `Self`.
|
|
// This is only possible for unevaluated constants, so we walk these here.
|
|
self.tcx.expand_abstract_consts(ct).super_visit_with(self)
|
|
}
|
|
}
|
|
|
|
struct EraseEscapingBoundRegions<'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
binder: ty::DebruijnIndex,
|
|
}
|
|
|
|
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseEscapingBoundRegions<'tcx> {
|
|
fn cx(&self) -> TyCtxt<'tcx> {
|
|
self.tcx
|
|
}
|
|
|
|
fn fold_binder<T>(&mut self, t: ty::Binder<'tcx, T>) -> ty::Binder<'tcx, T>
|
|
where
|
|
T: TypeFoldable<TyCtxt<'tcx>>,
|
|
{
|
|
self.binder.shift_in(1);
|
|
let result = t.super_fold_with(self);
|
|
self.binder.shift_out(1);
|
|
result
|
|
}
|
|
|
|
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
|
|
if let ty::ReBound(debruijn, _) = *r
|
|
&& debruijn < self.binder
|
|
{
|
|
r
|
|
} else {
|
|
self.tcx.lifetimes.re_erased
|
|
}
|
|
}
|
|
}
|
|
|
|
fn contains_illegal_impl_trait_in_trait<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
fn_def_id: DefId,
|
|
ty: ty::Binder<'tcx, Ty<'tcx>>,
|
|
) -> Option<MethodViolationCode> {
|
|
// This would be caught below, but rendering the error as a separate
|
|
// `async-specific` message is better.
|
|
if tcx.asyncness(fn_def_id).is_async() {
|
|
return Some(MethodViolationCode::AsyncFn);
|
|
}
|
|
|
|
// FIXME(RPITIT): Perhaps we should use a visitor here?
|
|
ty.skip_binder().walk().find_map(|arg| {
|
|
if let ty::GenericArgKind::Type(ty) = arg.unpack()
|
|
&& let ty::Alias(ty::Projection, proj) = ty.kind()
|
|
&& tcx.is_impl_trait_in_trait(proj.def_id)
|
|
{
|
|
Some(MethodViolationCode::ReferencesImplTraitInTrait(tcx.def_span(proj.def_id)))
|
|
} else {
|
|
None
|
|
}
|
|
})
|
|
}
|
|
|
|
pub(crate) fn provide(providers: &mut Providers) {
|
|
*providers = Providers {
|
|
dyn_compatibility_violations,
|
|
is_dyn_compatible,
|
|
generics_require_sized_self,
|
|
..*providers
|
|
};
|
|
}
|