bjoernager/rust
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Remove unnecessary layout assertions for object-safe receivers

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This commit is contained in:
Michael Goulet 2025-02-04 01:50:31 +00:00
parent f2c4ccd852
commit 0b26dc0b51
6 changed files with 42 additions and 173 deletions
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107
compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
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@ -4,19 +4,16 @@
//!
//! [^1]: Formerly known as "object safety".
use std::iter;
use std::ops::ControlFlow;
use rustc_abi::BackendRepr;
use rustc_errors::FatalError;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_middle::bug;
use rustc_middle::query::Providers;
use rustc_middle::ty::{
self, EarlyBinder, ExistentialPredicateStableCmpExt as _, GenericArgs, Ty, TyCtxt,
TypeFoldable, TypeFolder, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable,
TypeVisitableExt, TypeVisitor, TypingMode, Upcast,
self, EarlyBinder, GenericArgs, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, TypingMode, Upcast,
};
use rustc_span::Span;
use rustc_type_ir::elaborate;
@ -109,14 +106,6 @@ fn dyn_compatibility_violations_for_trait(
violations.push(DynCompatibilityViolation::SupertraitNonLifetimeBinder(spans));
}
if violations.is_empty() {
for item in tcx.associated_items(trait_def_id).in_definition_order() {
if let ty::AssocKind::Fn = item.kind {
check_receiver_correct(tcx, trait_def_id, *item);
}
}
}
violations
}
@ -499,55 +488,6 @@ fn virtual_call_violations_for_method<'tcx>(
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 typing_env = ty::TypingEnv::non_body_analysis(tcx, 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(typing_env.as_query_input(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(typing_env.as_query_input(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>(
@ -569,49 +509,6 @@ fn receiver_for_self_ty<'tcx>(
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: