773 lines
30 KiB
Rust
773 lines
30 KiB
Rust
//! "Object safety" refers to the ability for a trait to be converted
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//! to an object. In general, traits may only be converted to an
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//! object if all of their methods meet certain criteria. In particular,
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//! they must:
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//!
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//! - have a suitable receiver from which we can extract a vtable and coerce to a "thin" version
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//! that doesn't contain the vtable;
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//! - not reference the erased type `Self` except for in this receiver;
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//! - not have generic type parameters.
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use super::elaborate_predicates;
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use crate::infer::TyCtxtInferExt;
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use crate::traits::query::evaluate_obligation::InferCtxtExt;
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use crate::traits::{self, Obligation, ObligationCause};
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use rustc_errors::{Applicability, 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::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst};
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use rustc_middle::ty::{self, Predicate, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
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use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
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use rustc_span::symbol::Symbol;
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use rustc_span::Span;
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use smallvec::SmallVec;
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use std::iter;
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pub use crate::traits::{MethodViolationCode, ObjectSafetyViolation};
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/// Returns the object safety violations that affect
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/// astconv -- currently, `Self` in supertraits. This is needed
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/// because `object_safety_violations` can't be used during
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/// type collection.
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pub fn astconv_object_safety_violations(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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) -> Vec<ObjectSafetyViolation> {
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debug_assert!(tcx.generics_of(trait_def_id).has_self);
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let violations = traits::supertrait_def_ids(tcx, 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(ObjectSafetyViolation::SupertraitSelf)
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.collect();
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debug!("astconv_object_safety_violations(trait_def_id={:?}) = {:?}", trait_def_id, violations);
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violations
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}
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fn object_safety_violations(tcx: TyCtxt<'_>, trait_def_id: DefId) -> Vec<ObjectSafetyViolation> {
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debug_assert!(tcx.generics_of(trait_def_id).has_self);
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debug!("object_safety_violations: {:?}", trait_def_id);
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traits::supertrait_def_ids(tcx, trait_def_id)
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.flat_map(|def_id| object_safety_violations_for_trait(tcx, def_id))
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.collect()
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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 generics_require_sized_self(tcx, method.def_id) {
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return false;
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}
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match virtual_call_violation_for_method(tcx, trait_def_id, method) {
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None | Some(MethodViolationCode::WhereClauseReferencesSelf) => true,
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Some(_) => false,
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}
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}
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fn object_safety_violations_for_trait(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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) -> Vec<ObjectSafetyViolation> {
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// Check methods 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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.filter(|item| item.kind == ty::AssocKind::Method)
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.filter_map(|item| {
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object_safety_violation_for_method(tcx, trait_def_id, &item)
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.map(|(code, span)| ObjectSafetyViolation::Method(item.ident.name, code, span))
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})
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.filter(|violation| {
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if let ObjectSafetyViolation::Method(
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_,
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MethodViolationCode::WhereClauseReferencesSelf,
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span,
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) = violation
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{
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// Using `CRATE_NODE_ID` is wrong, but it's hard to get a more precise id.
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// It's also hard to get a use site span, so we use the method definition span.
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tcx.struct_span_lint_hir(
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WHERE_CLAUSES_OBJECT_SAFETY,
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hir::CRATE_HIR_ID,
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*span,
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|lint| {
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let mut err = lint.build(&format!(
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"the trait `{}` cannot be made into an object",
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tcx.def_path_str(trait_def_id)
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));
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let node = tcx.hir().get_if_local(trait_def_id);
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let msg = if let Some(hir::Node::Item(item)) = node {
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err.span_label(
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item.ident.span,
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"this trait cannot be made into an object...",
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);
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format!("...because {}", violation.error_msg())
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} else {
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format!(
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"the trait cannot be made into an object because {}",
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violation.error_msg()
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)
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};
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err.span_label(*span, &msg);
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match (node, violation.solution()) {
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(Some(_), Some((note, None))) => {
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err.help(¬e);
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}
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(Some(_), Some((note, Some((sugg, span))))) => {
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err.span_suggestion(
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span,
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¬e,
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sugg,
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Applicability::MachineApplicable,
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);
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}
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// Only provide the help if its a local trait, otherwise it's not actionable.
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_ => {}
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}
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err.emit();
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},
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);
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false
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} else {
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true
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}
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})
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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(ObjectSafetyViolation::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(ObjectSafetyViolation::SupertraitSelf(spans));
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}
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violations.extend(
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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::Const)
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.map(|item| ObjectSafetyViolation::AssocConst(item.ident.name, item.ident.span)),
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);
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debug!(
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"object_safety_violations_for_trait(trait_def_id={:?}) = {:?}",
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trait_def_id, violations
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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, hir::TraitBoundModifier::None)
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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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.where_clause
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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.super_predicates_of(trait_def_id)
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} else {
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tcx.predicates_of(trait_def_id)
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};
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let self_ty = tcx.types.self_param;
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let has_self_ty = |arg: &GenericArg<'_>| arg.walk().any(|arg| arg == self_ty.into());
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predicates
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.predicates
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.iter()
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.map(|(predicate, sp)| (predicate.subst_supertrait(tcx, &trait_ref), sp))
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.filter_map(|(predicate, &sp)| {
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match predicate {
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ty::Predicate::Trait(ref data, _) => {
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// In the case of a trait predicate, we can skip the "self" type.
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if data.skip_binder().trait_ref.substs[1..].iter().any(has_self_ty) {
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Some(sp)
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} else {
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None
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}
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}
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ty::Predicate::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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// 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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if data.skip_binder().projection_ty.trait_ref(tcx).substs[1..]
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.iter()
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.any(has_self_ty)
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{
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Some(sp)
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} else {
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None
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}
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}
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ty::Predicate::WellFormed(..)
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| ty::Predicate::ObjectSafe(..)
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| ty::Predicate::TypeOutlives(..)
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| ty::Predicate::RegionOutlives(..)
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| ty::Predicate::ClosureKind(..)
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| ty::Predicate::Subtype(..)
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| ty::Predicate::ConstEvaluatable(..) => None,
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}
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})
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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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generics_require_sized_self(tcx, 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 sized_def_id = match tcx.lang_items().sized_trait() {
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Some(def_id) => def_id,
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None => {
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return false; /* No Sized trait, can't require it! */
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}
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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_predicates(tcx, predicates).any(|predicate| match predicate {
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ty::Predicate::Trait(ref trait_pred, _) => {
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trait_pred.def_id() == sized_def_id && trait_pred.skip_binder().self_ty().is_param(0)
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}
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ty::Predicate::Projection(..)
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| ty::Predicate::Subtype(..)
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| ty::Predicate::RegionOutlives(..)
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| ty::Predicate::WellFormed(..)
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| ty::Predicate::ObjectSafe(..)
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| ty::Predicate::ClosureKind(..)
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| ty::Predicate::TypeOutlives(..)
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| ty::Predicate::ConstEvaluatable(..) => false,
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})
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}
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/// Returns `Some(_)` if this method makes the containing trait not object safe.
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fn object_safety_violation_for_method(
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tcx: TyCtxt<'_>,
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trait_def_id: DefId,
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method: &ty::AssocItem,
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) -> Option<(MethodViolationCode, Span)> {
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debug!("object_safety_violation_for_method({:?}, {:?})", trait_def_id, method);
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// Any method that has a `Self : Sized` requisite is otherwise
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// exempt from the regulations.
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if generics_require_sized_self(tcx, method.def_id) {
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return None;
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}
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let violation = virtual_call_violation_for_method(tcx, trait_def_id, method);
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// Get an accurate span depending on the violation.
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violation.map(|v| {
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let node = tcx.hir().get_if_local(method.def_id);
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let span = match (v, node) {
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(MethodViolationCode::ReferencesSelfInput(arg), Some(node)) => node
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.fn_decl()
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.and_then(|decl| decl.inputs.get(arg + 1))
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.map_or(method.ident.span, |arg| arg.span),
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(MethodViolationCode::UndispatchableReceiver, Some(node)) => node
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.fn_decl()
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.and_then(|decl| decl.inputs.get(0))
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.map_or(method.ident.span, |arg| arg.span),
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(MethodViolationCode::ReferencesSelfOutput, Some(node)) => {
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node.fn_decl().map_or(method.ident.span, |decl| decl.output.span())
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}
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_ => method.ident.span,
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};
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(v, span)
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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 not object safe, because the method might have a where clause
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/// `Self:Sized`.
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fn virtual_call_violation_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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) -> Option<MethodViolationCode> {
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// The method's first parameter must be named `self`
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if !method.method_has_self_argument {
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// We'll attempt to provide a structured suggestion for `Self: Sized`.
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let sugg =
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tcx.hir().get_if_local(method.def_id).as_ref().and_then(|node| node.generics()).map(
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|generics| match generics.where_clause.predicates {
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[] => (" where Self: Sized", generics.where_clause.span),
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[.., pred] => (", Self: Sized", pred.span().shrink_to_hi()),
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},
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);
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return Some(MethodViolationCode::StaticMethod(sugg));
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}
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let sig = tcx.fn_sig(method.def_id);
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for (i, input_ty) in sig.skip_binder().inputs()[1..].iter().enumerate() {
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if contains_illegal_self_type_reference(tcx, trait_def_id, input_ty) {
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return Some(MethodViolationCode::ReferencesSelfInput(i));
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}
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}
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if contains_illegal_self_type_reference(tcx, trait_def_id, sig.output().skip_binder()) {
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return Some(MethodViolationCode::ReferencesSelfOutput);
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}
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// We can't monomorphize things like `fn foo<A>(...)`.
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let own_counts = tcx.generics_of(method.def_id).own_counts();
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if own_counts.types + own_counts.consts != 0 {
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return Some(MethodViolationCode::Generic);
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}
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if tcx
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.predicates_of(method.def_id)
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.predicates
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.iter()
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// A trait object can't claim to live more than the concrete type,
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// so outlives predicates will always hold.
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.cloned()
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.filter(|(p, _)| p.to_opt_type_outlives().is_none())
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.collect::<Vec<_>>()
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// Do a shallow visit so that `contains_illegal_self_type_reference`
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// may apply it's custom visiting.
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.visit_tys_shallow(|t| contains_illegal_self_type_reference(tcx, trait_def_id, t))
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{
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return Some(MethodViolationCode::WhereClauseReferencesSelf);
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}
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let receiver_ty =
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tcx.liberate_late_bound_regions(method.def_id, &sig.map_bound(|sig| sig.inputs()[0]));
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// Until `unsized_locals` is fully implemented, `self: Self` can't be dispatched on.
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// However, this is already considered object-safe. We allow it as a special case here.
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// FIXME(mikeyhew) get rid of this `if` statement once `receiver_is_dispatchable` allows
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// `Receiver: Unsize<Receiver[Self => dyn Trait]>`.
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if receiver_ty != tcx.types.self_param {
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if !receiver_is_dispatchable(tcx, method, receiver_ty) {
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return Some(MethodViolationCode::UndispatchableReceiver);
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} else {
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// Do sanity check to make sure the receiver actually has the layout of a pointer.
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use rustc_target::abi::Abi;
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let param_env = tcx.param_env(method.def_id);
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let abi_of_ty = |ty: Ty<'tcx>| -> &Abi {
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match tcx.layout_of(param_env.and(ty)) {
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Ok(layout) => &layout.abi,
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Err(err) => bug!("error: {}\n while computing layout for type {:?}", err, ty),
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}
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};
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// e.g., `Rc<()>`
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let unit_receiver_ty =
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receiver_for_self_ty(tcx, receiver_ty, tcx.mk_unit(), method.def_id);
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match abi_of_ty(unit_receiver_ty) {
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&Abi::Scalar(..) => (),
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abi => {
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tcx.sess.delay_span_bug(
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tcx.def_span(method.def_id),
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&format!(
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"receiver when `Self = ()` should have a Scalar ABI; found {:?}",
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abi
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),
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);
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}
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}
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let trait_object_ty =
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object_ty_for_trait(tcx, trait_def_id, tcx.mk_region(ty::ReStatic));
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|
|
// e.g., `Rc<dyn Trait>`
|
|
let trait_object_receiver =
|
|
receiver_for_self_ty(tcx, receiver_ty, trait_object_ty, method.def_id);
|
|
|
|
match abi_of_ty(trait_object_receiver) {
|
|
&Abi::ScalarPair(..) => (),
|
|
abi => {
|
|
tcx.sess.delay_span_bug(
|
|
tcx.def_span(method.def_id),
|
|
&format!(
|
|
"receiver when `Self = {}` should have a ScalarPair ABI; \
|
|
found {:?}",
|
|
trait_object_ty, abi
|
|
),
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
None
|
|
}
|
|
|
|
/// Performs a type substitution 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 substs = InternalSubsts::for_item(tcx, method_def_id, |param, _| {
|
|
if param.index == 0 { self_ty.into() } else { tcx.mk_param_from_def(param) }
|
|
});
|
|
|
|
let result = receiver_ty.subst(tcx, substs);
|
|
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`.
|
|
fn object_ty_for_trait<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
trait_def_id: DefId,
|
|
lifetime: ty::Region<'tcx>,
|
|
) -> Ty<'tcx> {
|
|
debug!("object_ty_for_trait: trait_def_id={:?}", trait_def_id);
|
|
|
|
let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
|
|
|
|
let trait_predicate =
|
|
ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
|
|
|
|
let mut associated_types = traits::supertraits(tcx, ty::Binder::dummy(trait_ref))
|
|
.flat_map(|super_trait_ref| {
|
|
tcx.associated_items(super_trait_ref.def_id())
|
|
.in_definition_order()
|
|
.map(move |item| (super_trait_ref, item))
|
|
})
|
|
.filter(|(_, item)| item.kind == ty::AssocKind::Type)
|
|
.collect::<Vec<_>>();
|
|
|
|
// existential predicates need to be in a specific order
|
|
associated_types.sort_by_cached_key(|(_, item)| tcx.def_path_hash(item.def_id));
|
|
|
|
let projection_predicates = associated_types.into_iter().map(|(super_trait_ref, item)| {
|
|
// We *can* get bound lifetimes here in cases like
|
|
// `trait MyTrait: for<'s> OtherTrait<&'s T, Output=bool>`.
|
|
//
|
|
// binder moved to (*)...
|
|
let super_trait_ref = super_trait_ref.skip_binder();
|
|
ty::ExistentialPredicate::Projection(ty::ExistentialProjection {
|
|
ty: tcx.mk_projection(item.def_id, super_trait_ref.substs),
|
|
item_def_id: item.def_id,
|
|
substs: super_trait_ref.substs,
|
|
})
|
|
});
|
|
|
|
let existential_predicates =
|
|
tcx.mk_existential_predicates(iter::once(trait_predicate).chain(projection_predicates));
|
|
|
|
let object_ty = tcx.mk_dynamic(
|
|
// (*) ... binder re-introduced here
|
|
ty::Binder::bind(existential_predicates),
|
|
lifetime,
|
|
);
|
|
|
|
debug!("object_ty_for_trait: object_ty=`{}`", object_ty);
|
|
|
|
object_ty
|
|
}
|
|
|
|
/// 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:
|
|
///
|
|
/// ```
|
|
/// Receiver[Self => T]: DispatchFromDyn<Receiver[Self => dyn Trait]>
|
|
/// ```
|
|
///
|
|
/// where `Foo[X => Y]` means "the same type as `Foo`, but with `X` replaced with `Y`"
|
|
/// (substitution 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 object safe, creating a cycle (until object_safe_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:
|
|
///
|
|
/// 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>`.
|
|
#[allow(dead_code)]
|
|
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 (unsize_did, dispatch_from_dyn_did) = if let (Some(u), Some(cu)) = traits {
|
|
(u, cu)
|
|
} 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 object_safe_for_dispatch is stabilized, we can
|
|
// replace this with `dyn Trait`
|
|
let unsized_self_ty: Ty<'tcx> =
|
|
tcx.mk_ty_param(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 mut param_env = tcx.param_env(method.def_id);
|
|
|
|
// Self: Unsize<U>
|
|
let unsize_predicate = ty::TraitRef {
|
|
def_id: unsize_did,
|
|
substs: tcx.mk_substs_trait(tcx.types.self_param, &[unsized_self_ty.into()]),
|
|
}
|
|
.without_const()
|
|
.to_predicate();
|
|
|
|
// U: Trait<Arg1, ..., ArgN>
|
|
let trait_predicate = {
|
|
let substs =
|
|
InternalSubsts::for_item(tcx, method.container.assert_trait(), |param, _| {
|
|
if param.index == 0 {
|
|
unsized_self_ty.into()
|
|
} else {
|
|
tcx.mk_param_from_def(param)
|
|
}
|
|
});
|
|
|
|
ty::TraitRef { def_id: unsize_did, substs }.without_const().to_predicate()
|
|
};
|
|
|
|
let caller_bounds: Vec<Predicate<'tcx>> = param_env
|
|
.caller_bounds
|
|
.iter()
|
|
.cloned()
|
|
.chain(iter::once(unsize_predicate))
|
|
.chain(iter::once(trait_predicate))
|
|
.collect();
|
|
|
|
param_env.caller_bounds = tcx.intern_predicates(&caller_bounds);
|
|
|
|
param_env
|
|
};
|
|
|
|
// Receiver: DispatchFromDyn<Receiver[Self => U]>
|
|
let obligation = {
|
|
let predicate = ty::TraitRef {
|
|
def_id: dispatch_from_dyn_did,
|
|
substs: tcx.mk_substs_trait(receiver_ty, &[unsized_receiver_ty.into()]),
|
|
}
|
|
.without_const()
|
|
.to_predicate();
|
|
|
|
Obligation::new(ObligationCause::dummy(), param_env, predicate)
|
|
};
|
|
|
|
tcx.infer_ctxt().enter(|ref infcx| {
|
|
// the receiver is dispatchable iff the obligation holds
|
|
infcx.predicate_must_hold_modulo_regions(&obligation)
|
|
})
|
|
}
|
|
|
|
fn contains_illegal_self_type_reference<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
trait_def_id: DefId,
|
|
ty: Ty<'tcx>,
|
|
) -> bool {
|
|
// 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
|
|
// 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
|
|
// 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.
|
|
|
|
let mut supertraits: Option<Vec<ty::PolyTraitRef<'tcx>>> = None;
|
|
let self_ty = tcx.types.self_param;
|
|
|
|
let mut walker = ty.walk();
|
|
while let Some(arg) = walker.next() {
|
|
if arg == self_ty.into() {
|
|
return true;
|
|
}
|
|
|
|
// Special-case projections (everything else is walked normally).
|
|
if let GenericArgKind::Type(ty) = arg.unpack() {
|
|
if let ty::Projection(ref data) = ty.kind {
|
|
// This is a projected type `<Foo as SomeTrait>::X`.
|
|
|
|
// Compute supertraits of current trait lazily.
|
|
if supertraits.is_none() {
|
|
let trait_ref = ty::Binder::bind(ty::TraitRef::identity(tcx, trait_def_id));
|
|
supertraits = Some(traits::supertraits(tcx, 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 projection_trait_ref = ty::Binder::bind(data.trait_ref(tcx));
|
|
let is_supertrait_of_current_trait =
|
|
supertraits.as_ref().unwrap().contains(&projection_trait_ref);
|
|
|
|
if is_supertrait_of_current_trait {
|
|
// Do not walk contained types, do not report error, do collect $200.
|
|
walker.skip_current_subtree();
|
|
}
|
|
|
|
// DO walk contained types, POSSIBLY reporting an error.
|
|
}
|
|
}
|
|
|
|
// Walk contained types, if any.
|
|
}
|
|
|
|
false
|
|
}
|
|
|
|
pub fn provide(providers: &mut ty::query::Providers<'_>) {
|
|
*providers = ty::query::Providers { object_safety_violations, ..*providers };
|
|
}
|