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Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/mod.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/mod.rs | 863 |
1 files changed, 863 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs new file mode 100644 index 000000000..9c6bb0731 --- /dev/null +++ b/compiler/rustc_trait_selection/src/traits/mod.rs @@ -0,0 +1,863 @@ +//! Trait Resolution. See the [rustc dev guide] for more information on how this works. +//! +//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html + +pub mod auto_trait; +mod chalk_fulfill; +pub mod codegen; +mod coherence; +pub mod const_evaluatable; +mod engine; +pub mod error_reporting; +mod fulfill; +pub mod misc; +mod object_safety; +mod on_unimplemented; +mod project; +pub mod query; +pub(crate) mod relationships; +mod select; +mod specialize; +mod structural_match; +mod util; +pub mod wf; + +use crate::infer::outlives::env::OutlivesEnvironment; +use crate::infer::{InferCtxt, TyCtxtInferExt}; +use crate::traits::error_reporting::InferCtxtExt as _; +use crate::traits::query::evaluate_obligation::InferCtxtExt as _; +use rustc_errors::ErrorGuaranteed; +use rustc_hir as hir; +use rustc_hir::def_id::DefId; +use rustc_hir::lang_items::LangItem; +use rustc_middle::ty::fold::TypeFoldable; +use rustc_middle::ty::subst::{InternalSubsts, SubstsRef}; +use rustc_middle::ty::visit::TypeVisitable; +use rustc_middle::ty::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry}; +use rustc_span::{sym, Span}; +use smallvec::SmallVec; + +use std::fmt::Debug; +use std::ops::ControlFlow; + +pub use self::FulfillmentErrorCode::*; +pub use self::ImplSource::*; +pub use self::ObligationCauseCode::*; +pub use self::SelectionError::*; + +pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls}; +pub use self::coherence::{OrphanCheckErr, OverlapResult}; +pub use self::engine::{ObligationCtxt, TraitEngineExt}; +pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation}; +pub use self::object_safety::astconv_object_safety_violations; +pub use self::object_safety::is_vtable_safe_method; +pub use self::object_safety::MethodViolationCode; +pub use self::object_safety::ObjectSafetyViolation; +pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote}; +pub use self::project::{normalize, normalize_projection_type, normalize_to}; +pub use self::select::{EvaluationCache, SelectionCache, SelectionContext}; +pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError}; +pub use self::specialize::specialization_graph::FutureCompatOverlapError; +pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind; +pub use self::specialize::{specialization_graph, translate_substs, OverlapError}; +pub use self::structural_match::{ + search_for_adt_const_param_violation, search_for_structural_match_violation, +}; +pub use self::util::{ + elaborate_obligations, elaborate_predicates, elaborate_predicates_with_span, + elaborate_trait_ref, elaborate_trait_refs, +}; +pub use self::util::{expand_trait_aliases, TraitAliasExpander}; +pub use self::util::{ + get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices, +}; +pub use self::util::{ + supertrait_def_ids, supertraits, transitive_bounds, transitive_bounds_that_define_assoc_type, + SupertraitDefIds, Supertraits, +}; + +pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext; + +pub use rustc_infer::traits::*; + +/// Whether to skip the leak check, as part of a future compatibility warning step. +/// +/// The "default" for skip-leak-check corresponds to the current +/// behavior (do not skip the leak check) -- not the behavior we are +/// transitioning into. +#[derive(Copy, Clone, PartialEq, Eq, Debug, Default)] +pub enum SkipLeakCheck { + Yes, + #[default] + No, +} + +impl SkipLeakCheck { + fn is_yes(self) -> bool { + self == SkipLeakCheck::Yes + } +} + +/// The mode that trait queries run in. +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +pub enum TraitQueryMode { + /// Standard/un-canonicalized queries get accurate + /// spans etc. passed in and hence can do reasonable + /// error reporting on their own. + Standard, + /// Canonicalized queries get dummy spans and hence + /// must generally propagate errors to + /// pre-canonicalization callsites. + Canonical, +} + +/// Creates predicate obligations from the generic bounds. +pub fn predicates_for_generics<'tcx>( + cause: ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + generic_bounds: ty::InstantiatedPredicates<'tcx>, +) -> impl Iterator<Item = PredicateObligation<'tcx>> { + util::predicates_for_generics(cause, 0, param_env, generic_bounds) +} + +/// Determines whether the type `ty` is known to meet `bound` and +/// returns true if so. Returns false if `ty` either does not meet +/// `bound` or is not known to meet bound (note that this is +/// conservative towards *no impl*, which is the opposite of the +/// `evaluate` methods). +pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>( + infcx: &InferCtxt<'a, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + ty: Ty<'tcx>, + def_id: DefId, + span: Span, +) -> bool { + debug!( + "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})", + ty, + infcx.tcx.def_path_str(def_id) + ); + + let trait_ref = + ty::Binder::dummy(ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) }); + let obligation = Obligation { + param_env, + cause: ObligationCause::misc(span, hir::CRATE_HIR_ID), + recursion_depth: 0, + predicate: trait_ref.without_const().to_predicate(infcx.tcx), + }; + + let result = infcx.predicate_must_hold_modulo_regions(&obligation); + debug!( + "type_known_to_meet_ty={:?} bound={} => {:?}", + ty, + infcx.tcx.def_path_str(def_id), + result + ); + + if result && ty.has_infer_types_or_consts() { + // Because of inference "guessing", selection can sometimes claim + // to succeed while the success requires a guess. To ensure + // this function's result remains infallible, we must confirm + // that guess. While imperfect, I believe this is sound. + + // The handling of regions in this area of the code is terrible, + // see issue #29149. We should be able to improve on this with + // NLL. + let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx); + + // We can use a dummy node-id here because we won't pay any mind + // to region obligations that arise (there shouldn't really be any + // anyhow). + let cause = ObligationCause::misc(span, hir::CRATE_HIR_ID); + + fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause); + + // Note: we only assume something is `Copy` if we can + // *definitively* show that it implements `Copy`. Otherwise, + // assume it is move; linear is always ok. + match fulfill_cx.select_all_or_error(infcx).as_slice() { + [] => { + debug!( + "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success", + ty, + infcx.tcx.def_path_str(def_id) + ); + true + } + errors => { + debug!( + ?ty, + bound = %infcx.tcx.def_path_str(def_id), + ?errors, + "type_known_to_meet_bound_modulo_regions" + ); + false + } + } + } else { + result + } +} + +#[instrument(level = "debug", skip(tcx, elaborated_env))] +fn do_normalize_predicates<'tcx>( + tcx: TyCtxt<'tcx>, + cause: ObligationCause<'tcx>, + elaborated_env: ty::ParamEnv<'tcx>, + predicates: Vec<ty::Predicate<'tcx>>, +) -> Result<Vec<ty::Predicate<'tcx>>, ErrorGuaranteed> { + let span = cause.span; + // FIXME. We should really... do something with these region + // obligations. But this call just continues the older + // behavior (i.e., doesn't cause any new bugs), and it would + // take some further refactoring to actually solve them. In + // particular, we would have to handle implied bounds + // properly, and that code is currently largely confined to + // regionck (though I made some efforts to extract it + // out). -nmatsakis + // + // @arielby: In any case, these obligations are checked + // by wfcheck anyway, so I'm not sure we have to check + // them here too, and we will remove this function when + // we move over to lazy normalization *anyway*. + tcx.infer_ctxt().ignoring_regions().enter(|infcx| { + let fulfill_cx = FulfillmentContext::new(); + let predicates = + match fully_normalize(&infcx, fulfill_cx, cause, elaborated_env, predicates) { + Ok(predicates) => predicates, + Err(errors) => { + let reported = infcx.report_fulfillment_errors(&errors, None, false); + return Err(reported); + } + }; + + debug!("do_normalize_predictes: normalized predicates = {:?}", predicates); + + // We can use the `elaborated_env` here; the region code only + // cares about declarations like `'a: 'b`. + let outlives_env = OutlivesEnvironment::new(elaborated_env); + + // FIXME: It's very weird that we ignore region obligations but apparently + // still need to use `resolve_regions` as we need the resolved regions in + // the normalized predicates. + let errors = infcx.resolve_regions(&outlives_env); + if !errors.is_empty() { + tcx.sess.delay_span_bug( + span, + format!( + "failed region resolution while normalizing {elaborated_env:?}: {errors:?}" + ), + ); + } + + match infcx.fully_resolve(predicates) { + Ok(predicates) => Ok(predicates), + Err(fixup_err) => { + // If we encounter a fixup error, it means that some type + // variable wound up unconstrained. I actually don't know + // if this can happen, and I certainly don't expect it to + // happen often, but if it did happen it probably + // represents a legitimate failure due to some kind of + // unconstrained variable. + // + // @lcnr: Let's still ICE here for now. I want a test case + // for that. + span_bug!( + span, + "inference variables in normalized parameter environment: {}", + fixup_err + ); + } + } + }) +} + +// FIXME: this is gonna need to be removed ... +/// Normalizes the parameter environment, reporting errors if they occur. +#[instrument(level = "debug", skip(tcx))] +pub fn normalize_param_env_or_error<'tcx>( + tcx: TyCtxt<'tcx>, + unnormalized_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, +) -> ty::ParamEnv<'tcx> { + // I'm not wild about reporting errors here; I'd prefer to + // have the errors get reported at a defined place (e.g., + // during typeck). Instead I have all parameter + // environments, in effect, going through this function + // and hence potentially reporting errors. This ensures of + // course that we never forget to normalize (the + // alternative seemed like it would involve a lot of + // manual invocations of this fn -- and then we'd have to + // deal with the errors at each of those sites). + // + // In any case, in practice, typeck constructs all the + // parameter environments once for every fn as it goes, + // and errors will get reported then; so outside of type inference we + // can be sure that no errors should occur. + let mut predicates: Vec<_> = + util::elaborate_predicates(tcx, unnormalized_env.caller_bounds().into_iter()) + .map(|obligation| obligation.predicate) + .collect(); + + debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates); + + let elaborated_env = ty::ParamEnv::new( + tcx.intern_predicates(&predicates), + unnormalized_env.reveal(), + unnormalized_env.constness(), + ); + + // HACK: we are trying to normalize the param-env inside *itself*. The problem is that + // normalization expects its param-env to be already normalized, which means we have + // a circularity. + // + // The way we handle this is by normalizing the param-env inside an unnormalized version + // of the param-env, which means that if the param-env contains unnormalized projections, + // we'll have some normalization failures. This is unfortunate. + // + // Lazy normalization would basically handle this by treating just the + // normalizing-a-trait-ref-requires-itself cycles as evaluation failures. + // + // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated + // types, so to make the situation less bad, we normalize all the predicates *but* + // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and + // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment. + // + // This works fairly well because trait matching does not actually care about param-env + // TypeOutlives predicates - these are normally used by regionck. + let outlives_predicates: Vec<_> = predicates + .drain_filter(|predicate| { + matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..)) + }) + .collect(); + + debug!( + "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})", + predicates, outlives_predicates + ); + let Ok(non_outlives_predicates) = do_normalize_predicates( + tcx, + cause.clone(), + elaborated_env, + predicates, + ) else { + // An unnormalized env is better than nothing. + debug!("normalize_param_env_or_error: errored resolving non-outlives predicates"); + return elaborated_env; + }; + + debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates); + + // Not sure whether it is better to include the unnormalized TypeOutlives predicates + // here. I believe they should not matter, because we are ignoring TypeOutlives param-env + // predicates here anyway. Keeping them here anyway because it seems safer. + let outlives_env: Vec<_> = + non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect(); + let outlives_env = ty::ParamEnv::new( + tcx.intern_predicates(&outlives_env), + unnormalized_env.reveal(), + unnormalized_env.constness(), + ); + let Ok(outlives_predicates) = do_normalize_predicates( + tcx, + cause, + outlives_env, + outlives_predicates, + ) else { + // An unnormalized env is better than nothing. + debug!("normalize_param_env_or_error: errored resolving outlives predicates"); + return elaborated_env; + }; + debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates); + + let mut predicates = non_outlives_predicates; + predicates.extend(outlives_predicates); + debug!("normalize_param_env_or_error: final predicates={:?}", predicates); + ty::ParamEnv::new( + tcx.intern_predicates(&predicates), + unnormalized_env.reveal(), + unnormalized_env.constness(), + ) +} + +pub fn fully_normalize<'a, 'tcx, T>( + infcx: &InferCtxt<'a, 'tcx>, + mut fulfill_cx: FulfillmentContext<'tcx>, + cause: ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + value: T, +) -> Result<T, Vec<FulfillmentError<'tcx>>> +where + T: TypeFoldable<'tcx>, +{ + debug!("fully_normalize_with_fulfillcx(value={:?})", value); + let selcx = &mut SelectionContext::new(infcx); + let Normalized { value: normalized_value, obligations } = + project::normalize(selcx, param_env, cause, value); + debug!( + "fully_normalize: normalized_value={:?} obligations={:?}", + normalized_value, obligations + ); + for obligation in obligations { + fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation); + } + + debug!("fully_normalize: select_all_or_error start"); + let errors = fulfill_cx.select_all_or_error(infcx); + if !errors.is_empty() { + return Err(errors); + } + debug!("fully_normalize: select_all_or_error complete"); + let resolved_value = infcx.resolve_vars_if_possible(normalized_value); + debug!("fully_normalize: resolved_value={:?}", resolved_value); + Ok(resolved_value) +} + +/// Normalizes the predicates and checks whether they hold in an empty environment. If this +/// returns true, then either normalize encountered an error or one of the predicates did not +/// hold. Used when creating vtables to check for unsatisfiable methods. +pub fn impossible_predicates<'tcx>( + tcx: TyCtxt<'tcx>, + predicates: Vec<ty::Predicate<'tcx>>, +) -> bool { + debug!("impossible_predicates(predicates={:?})", predicates); + + let result = tcx.infer_ctxt().enter(|infcx| { + // HACK: Set tainted by errors to gracefully exit in case of overflow. + infcx.set_tainted_by_errors(); + + let param_env = ty::ParamEnv::reveal_all(); + let mut selcx = SelectionContext::new(&infcx); + let mut fulfill_cx = FulfillmentContext::new(); + let cause = ObligationCause::dummy(); + let Normalized { value: predicates, obligations } = + normalize(&mut selcx, param_env, cause.clone(), predicates); + for obligation in obligations { + fulfill_cx.register_predicate_obligation(&infcx, obligation); + } + for predicate in predicates { + let obligation = Obligation::new(cause.clone(), param_env, predicate); + fulfill_cx.register_predicate_obligation(&infcx, obligation); + } + + let errors = fulfill_cx.select_all_or_error(&infcx); + + // Clean up after ourselves + let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types(); + + !errors.is_empty() + }); + debug!("impossible_predicates = {:?}", result); + result +} + +fn subst_and_check_impossible_predicates<'tcx>( + tcx: TyCtxt<'tcx>, + key: (DefId, SubstsRef<'tcx>), +) -> bool { + debug!("subst_and_check_impossible_predicates(key={:?})", key); + + let mut predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates; + + // Specifically check trait fulfillment to avoid an error when trying to resolve + // associated items. + if let Some(trait_def_id) = tcx.trait_of_item(key.0) { + let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, key.1); + predicates.push(ty::Binder::dummy(trait_ref).to_poly_trait_predicate().to_predicate(tcx)); + } + + predicates.retain(|predicate| !predicate.needs_subst()); + let result = impossible_predicates(tcx, predicates); + + debug!("subst_and_check_impossible_predicates(key={:?}) = {:?}", key, result); + result +} + +#[derive(Clone, Debug)] +enum VtblSegment<'tcx> { + MetadataDSA, + TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool }, +} + +/// Prepare the segments for a vtable +fn prepare_vtable_segments<'tcx, T>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::PolyTraitRef<'tcx>, + mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>, +) -> Option<T> { + // The following constraints holds for the final arrangement. + // 1. The whole virtual table of the first direct super trait is included as the + // the prefix. If this trait doesn't have any super traits, then this step + // consists of the dsa metadata. + // 2. Then comes the proper pointer metadata(vptr) and all own methods for all + // other super traits except those already included as part of the first + // direct super trait virtual table. + // 3. finally, the own methods of this trait. + + // This has the advantage that trait upcasting to the first direct super trait on each level + // is zero cost, and to another trait includes only replacing the pointer with one level indirection, + // while not using too much extra memory. + + // For a single inheritance relationship like this, + // D --> C --> B --> A + // The resulting vtable will consists of these segments: + // DSA, A, B, C, D + + // For a multiple inheritance relationship like this, + // D --> C --> A + // \-> B + // The resulting vtable will consists of these segments: + // DSA, A, B, B-vptr, C, D + + // For a diamond inheritance relationship like this, + // D --> B --> A + // \-> C -/ + // The resulting vtable will consists of these segments: + // DSA, A, B, C, C-vptr, D + + // For a more complex inheritance relationship like this: + // O --> G --> C --> A + // \ \ \-> B + // | |-> F --> D + // | \-> E + // |-> N --> J --> H + // \ \-> I + // |-> M --> K + // \-> L + // The resulting vtable will consists of these segments: + // DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G, + // H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr, + // N, N-vptr, O + + // emit dsa segment first. + if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) { + return Some(v); + } + + let mut emit_vptr_on_new_entry = false; + let mut visited = util::PredicateSet::new(tcx); + let predicate = trait_ref.without_const().to_predicate(tcx); + let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> = + smallvec![(trait_ref, emit_vptr_on_new_entry, None)]; + visited.insert(predicate); + + // the main traversal loop: + // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes + // that each node is emitted after all its descendents have been emitted. + // so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set. + // this is done on the fly. + // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it + // stops after it finds a node that has a next-sibling node. + // This next-sibling node will used as the starting point of next slice. + + // Example: + // For a diamond inheritance relationship like this, + // D#1 --> B#0 --> A#0 + // \-> C#1 -/ + + // Starting point 0 stack [D] + // Loop run #0: Stack after diving in is [D B A], A is "childless" + // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one. + // Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here. + // Loop run #0: Stack after exiting out is [D C], C is the next starting point. + // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted). + // Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node. + // Loop run #1: Stack after exiting out is []. Now the function exits. + + loop { + // dive deeper into the stack, recording the path + 'diving_in: loop { + if let Some((inner_most_trait_ref, _, _)) = stack.last() { + let inner_most_trait_ref = *inner_most_trait_ref; + let mut direct_super_traits_iter = tcx + .super_predicates_of(inner_most_trait_ref.def_id()) + .predicates + .into_iter() + .filter_map(move |(pred, _)| { + pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred() + }); + + 'diving_in_skip_visited_traits: loop { + if let Some(next_super_trait) = direct_super_traits_iter.next() { + if visited.insert(next_super_trait.to_predicate(tcx)) { + // We're throwing away potential constness of super traits here. + // FIXME: handle ~const super traits + let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref); + stack.push(( + next_super_trait, + emit_vptr_on_new_entry, + Some(direct_super_traits_iter), + )); + break 'diving_in_skip_visited_traits; + } else { + continue 'diving_in_skip_visited_traits; + } + } else { + break 'diving_in; + } + } + } + } + + // Other than the left-most path, vptr should be emitted for each trait. + emit_vptr_on_new_entry = true; + + // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level. + 'exiting_out: loop { + if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() { + if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries { + trait_ref: *inner_most_trait_ref, + emit_vptr: *emit_vptr, + }) { + return Some(v); + } + + 'exiting_out_skip_visited_traits: loop { + if let Some(siblings) = siblings_opt { + if let Some(next_inner_most_trait_ref) = siblings.next() { + if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) { + // We're throwing away potential constness of super traits here. + // FIXME: handle ~const super traits + let next_inner_most_trait_ref = + next_inner_most_trait_ref.map_bound(|t| t.trait_ref); + *inner_most_trait_ref = next_inner_most_trait_ref; + *emit_vptr = emit_vptr_on_new_entry; + break 'exiting_out; + } else { + continue 'exiting_out_skip_visited_traits; + } + } + } + stack.pop(); + continue 'exiting_out; + } + } + // all done + return None; + } + } +} + +fn dump_vtable_entries<'tcx>( + tcx: TyCtxt<'tcx>, + sp: Span, + trait_ref: ty::PolyTraitRef<'tcx>, + entries: &[VtblEntry<'tcx>], +) { + let msg = format!("vtable entries for `{}`: {:#?}", trait_ref, entries); + tcx.sess.struct_span_err(sp, &msg).emit(); +} + +fn own_existential_vtable_entries<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::PolyExistentialTraitRef<'tcx>, +) -> &'tcx [DefId] { + let trait_methods = tcx + .associated_items(trait_ref.def_id()) + .in_definition_order() + .filter(|item| item.kind == ty::AssocKind::Fn); + // Now list each method's DefId (for within its trait). + let own_entries = trait_methods.filter_map(move |trait_method| { + debug!("own_existential_vtable_entry: trait_method={:?}", trait_method); + let def_id = trait_method.def_id; + + // Some methods cannot be called on an object; skip those. + if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) { + debug!("own_existential_vtable_entry: not vtable safe"); + return None; + } + + Some(def_id) + }); + + tcx.arena.alloc_from_iter(own_entries.into_iter()) +} + +/// Given a trait `trait_ref`, iterates the vtable entries +/// that come from `trait_ref`, including its supertraits. +fn vtable_entries<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::PolyTraitRef<'tcx>, +) -> &'tcx [VtblEntry<'tcx>] { + debug!("vtable_entries({:?})", trait_ref); + + let mut entries = vec![]; + + let vtable_segment_callback = |segment| -> ControlFlow<()> { + match segment { + VtblSegment::MetadataDSA => { + entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES); + } + VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => { + let existential_trait_ref = trait_ref + .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)); + + // Lookup the shape of vtable for the trait. + let own_existential_entries = + tcx.own_existential_vtable_entries(existential_trait_ref); + + let own_entries = own_existential_entries.iter().copied().map(|def_id| { + debug!("vtable_entries: trait_method={:?}", def_id); + + // The method may have some early-bound lifetimes; add regions for those. + let substs = trait_ref.map_bound(|trait_ref| { + InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind { + GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(), + GenericParamDefKind::Type { .. } + | GenericParamDefKind::Const { .. } => { + trait_ref.substs[param.index as usize] + } + }) + }); + + // The trait type may have higher-ranked lifetimes in it; + // erase them if they appear, so that we get the type + // at some particular call site. + let substs = tcx + .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs); + + // It's possible that the method relies on where-clauses that + // do not hold for this particular set of type parameters. + // Note that this method could then never be called, so we + // do not want to try and codegen it, in that case (see #23435). + let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs); + if impossible_predicates(tcx, predicates.predicates) { + debug!("vtable_entries: predicates do not hold"); + return VtblEntry::Vacant; + } + + let instance = ty::Instance::resolve_for_vtable( + tcx, + ty::ParamEnv::reveal_all(), + def_id, + substs, + ) + .expect("resolution failed during building vtable representation"); + VtblEntry::Method(instance) + }); + + entries.extend(own_entries); + + if emit_vptr { + entries.push(VtblEntry::TraitVPtr(trait_ref)); + } + } + } + + ControlFlow::Continue(()) + }; + + let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback); + + if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) { + let sp = tcx.def_span(trait_ref.def_id()); + dump_vtable_entries(tcx, sp, trait_ref, &entries); + } + + tcx.arena.alloc_from_iter(entries.into_iter()) +} + +/// Find slot base for trait methods within vtable entries of another trait +fn vtable_trait_first_method_offset<'tcx>( + tcx: TyCtxt<'tcx>, + key: ( + ty::PolyTraitRef<'tcx>, // trait_to_be_found + ty::PolyTraitRef<'tcx>, // trait_owning_vtable + ), +) -> usize { + let (trait_to_be_found, trait_owning_vtable) = key; + + // #90177 + let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found); + + let vtable_segment_callback = { + let mut vtable_base = 0; + + move |segment| { + match segment { + VtblSegment::MetadataDSA => { + vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len(); + } + VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => { + if tcx.erase_regions(trait_ref) == trait_to_be_found_erased { + return ControlFlow::Break(vtable_base); + } + vtable_base += util::count_own_vtable_entries(tcx, trait_ref); + if emit_vptr { + vtable_base += 1; + } + } + } + ControlFlow::Continue(()) + } + }; + + if let Some(vtable_base) = + prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback) + { + vtable_base + } else { + bug!("Failed to find info for expected trait in vtable"); + } +} + +/// Find slot offset for trait vptr within vtable entries of another trait +pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>( + tcx: TyCtxt<'tcx>, + key: ( + Ty<'tcx>, // trait object type whose trait owning vtable + Ty<'tcx>, // trait object for supertrait + ), +) -> Option<usize> { + let (source, target) = key; + assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer()); + assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer()); + + // this has been typecked-before, so diagnostics is not really needed. + let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None); + + let trait_ref = ty::TraitRef { + def_id: unsize_trait_did, + substs: tcx.mk_substs_trait(source, &[target.into()]), + }; + let obligation = Obligation::new( + ObligationCause::dummy(), + ty::ParamEnv::reveal_all(), + ty::Binder::dummy(ty::TraitPredicate { + trait_ref, + constness: ty::BoundConstness::NotConst, + polarity: ty::ImplPolarity::Positive, + }), + ); + + let implsrc = tcx.infer_ctxt().enter(|infcx| { + let mut selcx = SelectionContext::new(&infcx); + selcx.select(&obligation).unwrap() + }); + + let Some(ImplSource::TraitUpcasting(implsrc_traitcasting)) = implsrc else { + bug!(); + }; + + implsrc_traitcasting.vtable_vptr_slot +} + +pub fn provide(providers: &mut ty::query::Providers) { + object_safety::provide(providers); + structural_match::provide(providers); + *providers = ty::query::Providers { + specialization_graph_of: specialize::specialization_graph_provider, + specializes: specialize::specializes, + codegen_fulfill_obligation: codegen::codegen_fulfill_obligation, + own_existential_vtable_entries, + vtable_entries, + vtable_trait_upcasting_coercion_new_vptr_slot, + subst_and_check_impossible_predicates, + try_unify_abstract_consts: |tcx, param_env_and| { + let (param_env, (a, b)) = param_env_and.into_parts(); + const_evaluatable::try_unify_abstract_consts(tcx, (a, b), param_env) + }, + ..*providers + }; +} |