})
}
- fn take_opaque_types_for_query_response(&self) -> Vec<(Ty<'tcx>, Ty<'tcx>)> {
+ /// FIXME: This method should only be used for canonical queries and therefore be private.
+ ///
+ /// As the new solver does canonicalization slightly differently, this is also used there
+ /// for now. This should hopefully change fairly soon.
+ pub fn take_opaque_types_for_query_response(&self) -> Vec<(Ty<'tcx>, Ty<'tcx>)> {
self.inner
.borrow_mut()
.opaque_type_storage
let Canonical { max_universe, variables, value } = self;
Canonical { max_universe, variables, value: map_op(value) }
}
+
+ /// Allows you to map the `value` of a canonical while keeping the same set of
+ /// bound variables.
+ ///
+ /// **WARNING:** This function is very easy to mis-use, hence the name! See
+ /// the comment of [Canonical::unchecked_map] for more details.
+ pub fn unchecked_rebind<W>(self, value: W) -> Canonical<'tcx, W> {
+ let Canonical { max_universe, variables, value: _ } = self;
+ Canonical { max_universe, variables, value }
+ }
}
pub type QueryOutlivesConstraint<'tcx> = (
pub type CanonicalTypeOpNormalizeGoal<'tcx, T> =
Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::Normalize<T>>>;
-#[derive(Copy, Clone, Debug, HashStable)]
+#[derive(Copy, Clone, Debug, HashStable, PartialEq, Eq)]
pub struct NoSolution;
pub type Fallible<T> = Result<T, NoSolution>;
}
/// Information about the most specialized definition of an associated item.
+#[derive(Debug)]
pub struct LeafDef {
/// The associated item described by this `LeafDef`.
pub item: ty::AssocItem,
self
}
+ #[instrument(level = "debug", skip(tcx), ret)]
+ pub fn is_coinductive(self, tcx: TyCtxt<'tcx>) -> bool {
+ match self.kind().skip_binder() {
+ ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
+ tcx.trait_is_coinductive(data.def_id())
+ }
+ ty::PredicateKind::WellFormed(_) => true,
+ _ => false,
+ }
+ }
+
/// Whether this projection can be soundly normalized.
///
/// Wf predicates must not be normalized, as normalization
pub term: Term<'tcx>,
}
+impl<'tcx> ProjectionPredicate<'tcx> {
+ pub fn self_ty(self) -> Ty<'tcx> {
+ self.projection_ty.self_ty()
+ }
+
+ pub fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ProjectionPredicate<'tcx> {
+ Self { projection_ty: self.projection_ty.with_self_ty(tcx, self_ty), ..self }
+ }
+
+ pub fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId {
+ self.projection_ty.trait_def_id(tcx)
+ }
+
+ pub fn def_id(self) -> DefId {
+ self.projection_ty.def_id
+ }
+}
+
pub type PolyProjectionPredicate<'tcx> = Binder<'tcx, ProjectionPredicate<'tcx>>;
impl<'tcx> PolyProjectionPredicate<'tcx> {
}
}
-impl<'tcx> ProjectionPredicate<'tcx> {
- pub fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
- Self {
- projection_ty: tcx.mk_alias_ty(
- self.projection_ty.def_id,
- [self_ty.into()].into_iter().chain(self.projection_ty.substs.iter().skip(1)),
- ),
- ..self
- }
- }
-}
-
pub trait ToPolyTraitRef<'tcx> {
fn to_poly_trait_ref(&self) -> PolyTraitRef<'tcx>;
}
}
impl<'tcx> AliasTy<'tcx> {
- pub fn trait_def_id(&self, tcx: TyCtxt<'tcx>) -> DefId {
+ pub fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId {
match tcx.def_kind(self.def_id) {
DefKind::AssocTy | DefKind::AssocConst => tcx.parent(self.def_id),
DefKind::ImplTraitPlaceholder => {
/// For example, if this is a projection of `<T as StreamingIterator>::Item<'a>`,
/// then this function would return a `T: Iterator` trait reference and `['a]` as the own substs
pub fn trait_ref_and_own_substs(
- &self,
+ self,
tcx: TyCtxt<'tcx>,
) -> (ty::TraitRef<'tcx>, &'tcx [ty::GenericArg<'tcx>]) {
debug_assert!(matches!(tcx.def_kind(self.def_id), DefKind::AssocTy | DefKind::AssocConst));
/// WARNING: This will drop the substs for generic associated types
/// consider calling [Self::trait_ref_and_own_substs] to get those
/// as well.
- pub fn trait_ref(&self, tcx: TyCtxt<'tcx>) -> ty::TraitRef<'tcx> {
+ pub fn trait_ref(self, tcx: TyCtxt<'tcx>) -> ty::TraitRef<'tcx> {
let def_id = self.trait_def_id(tcx);
tcx.mk_trait_ref(def_id, self.substs.truncate_to(tcx, tcx.generics_of(def_id)))
}
- pub fn self_ty(&self) -> Ty<'tcx> {
+ pub fn self_ty(self) -> Ty<'tcx> {
self.substs.type_at(0)
}
+
+ pub fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
+ tcx.mk_alias_ty(self.def_id, [self_ty.into()].into_iter().chain(self.substs.iter().skip(1)))
+ }
}
#[derive(Copy, Clone, Debug, TypeFoldable, TypeVisitable, Lift)]
pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
EarlyBinder(value)
}
+
+ pub fn skip_binder(self) -> T {
+ self.0
+ }
}
impl<T> EarlyBinder<Option<T>> {
#![feature(let_chains)]
#![feature(if_let_guard)]
#![feature(never_type)]
+#![feature(result_option_inspect)]
#![feature(type_alias_impl_trait)]
#![recursion_limit = "512"] // For rustdoc
pub mod autoderef;
pub mod errors;
pub mod infer;
+pub mod solve;
pub mod traits;
--- /dev/null
+//! This module both handles the global cache which stores "finished" goals,
+//! and the provisional cache which contains partially computed goals.
+//!
+//! The provisional cache is necessary when dealing with coinductive cycles.
+//!
+//! For more information about the provisional cache and coinduction in general,
+//! check out the relevant section of the rustc-dev-guide.
+//!
+//! FIXME(@lcnr): Write that section, feel free to ping me if you need help here
+//! before then or if I still haven't done that before January 2023.
+use super::overflow::OverflowData;
+use super::CanonicalGoal;
+use super::{EvalCtxt, QueryResult};
+
+use rustc_data_structures::fx::FxHashMap;
+use rustc_middle::ty::TyCtxt;
+use std::{cmp::Ordering, collections::hash_map::Entry};
+
+#[derive(Debug, Clone)]
+struct ProvisionalEntry<'tcx> {
+ // In case we have a coinductive cycle, this is the
+ // the currently least restrictive result of this goal.
+ response: QueryResult<'tcx>,
+ // The lowest element on the stack on which this result
+ // relies on. Starts out as just being the depth at which
+ // we've proven this obligation, but gets lowered to the
+ // depth of another goal if we rely on it in a cycle.
+ depth: usize,
+}
+
+struct StackElem<'tcx> {
+ goal: CanonicalGoal<'tcx>,
+ has_been_used: bool,
+}
+
+/// The cache used for goals which are currently in progress or which depend
+/// on in progress results.
+///
+/// Once we're done with a goal we can store it in the global trait solver
+/// cache of the `TyCtxt`. For goals which we're currently proving, or which
+/// have only been proven via a coinductive cycle using a goal still on our stack
+/// we have to use this separate data structure.
+///
+/// The current data structure is not perfect, so there may still be room for
+/// improvement here. We have the following requirements:
+///
+/// ## Is there is a provisional entry for the given goal:
+///
+/// ```ignore (for syntax highlighting)
+/// self.entries.get(goal)
+/// ```
+///
+/// ## Get all goals on the stack involved in a cycle:
+///
+/// ```ignore (for syntax highlighting)
+/// let entry = self.entries.get(goal).unwrap();
+/// let involved_goals = self.stack.iter().skip(entry.depth);
+/// ```
+///
+/// ## Capping the depth of all entries
+///
+/// Needed whenever we encounter a cycle. The current implementation always
+/// iterates over all entries instead of only the ones with a larger depth.
+/// Changing this may result in notable performance improvements.
+///
+/// ```ignore (for syntax highlighting)
+/// let cycle_depth = self.entries.get(goal).unwrap().depth;
+/// for e in &mut self.entries {
+/// e.depth = e.depth.min(cycle_depth);
+/// }
+/// ```
+///
+/// ## Checking whether we have to rerun the current goal
+///
+/// A goal has to be rerun if its provisional result was used in a cycle
+/// and that result is different from its final result. We update
+/// [StackElem::has_been_used] for the deepest stack element involved in a cycle.
+///
+/// ## Moving all finished goals into the global cache
+///
+/// If `stack_elem.has_been_used` is true, iterate over all entries, moving the ones
+/// with equal depth. If not, simply move this single entry.
+pub(super) struct ProvisionalCache<'tcx> {
+ stack: Vec<StackElem<'tcx>>,
+ entries: FxHashMap<CanonicalGoal<'tcx>, ProvisionalEntry<'tcx>>,
+}
+
+impl<'tcx> ProvisionalCache<'tcx> {
+ pub(super) fn empty() -> ProvisionalCache<'tcx> {
+ ProvisionalCache { stack: Vec::new(), entries: Default::default() }
+ }
+
+ pub(super) fn current_depth(&self) -> usize {
+ self.stack.len()
+ }
+}
+
+impl<'tcx> EvalCtxt<'tcx> {
+ /// Tries putting the new goal on the stack, returning an error if it is already cached.
+ ///
+ /// This correctly updates the provisional cache if there is a cycle.
+ pub(super) fn try_push_stack(
+ &mut self,
+ goal: CanonicalGoal<'tcx>,
+ ) -> Result<(), QueryResult<'tcx>> {
+ // FIXME: start by checking the global cache
+
+ // Look at the provisional cache to check for cycles.
+ let cache = &mut self.provisional_cache;
+ match cache.entries.entry(goal) {
+ // No entry, simply push this goal on the stack after dealing with overflow.
+ Entry::Vacant(v) => {
+ if self.overflow_data.has_overflow(cache.stack.len()) {
+ return Err(self.deal_with_overflow());
+ }
+
+ v.insert(ProvisionalEntry {
+ response: fixme_response_yes_no_constraints(),
+ depth: cache.stack.len(),
+ });
+ cache.stack.push(StackElem { goal, has_been_used: false });
+ Ok(())
+ }
+ // We have a nested goal which relies on a goal `root` deeper in the stack.
+ //
+ // We first store that we may have to rerun `evaluate_goal` for `root` in case the
+ // provisional response is not equal to the final response. We also update the depth
+ // of all goals which recursively depend on our current goal to depend on `root`
+ // instead.
+ //
+ // Finally we can return either the provisional response for that goal if we have a
+ // coinductive cycle or an ambiguous result if the cycle is inductive.
+ Entry::Occupied(entry) => {
+ // FIXME: `ProvisionalEntry` should be `Copy`.
+ let entry = entry.get().clone();
+ cache.stack[entry.depth].has_been_used = true;
+ for provisional_entry in cache.entries.values_mut() {
+ provisional_entry.depth = provisional_entry.depth.min(entry.depth);
+ }
+
+ // NOTE: The goals on the stack aren't the only goals involved in this cycle.
+ // We can also depend on goals which aren't part of the stack but coinductively
+ // depend on the stack themselves. We already checked whether all the goals
+ // between these goals and their root on the stack. This means that as long as
+ // each goal in a cycle is checked for coinductivity by itself simply checking
+ // the stack is enough.
+ if cache.stack[entry.depth..]
+ .iter()
+ .all(|g| g.goal.value.predicate.is_coinductive(self.tcx))
+ {
+ Err(entry.response)
+ } else {
+ Err(fixme_response_maybe_no_constraints())
+ }
+ }
+ }
+ }
+
+ /// We cannot simply store the result of [EvalCtxt::compute_goal] as we have to deal with
+ /// coinductive cycles.
+ ///
+ /// When we encounter a coinductive cycle, we have to prove the final result of that cycle
+ /// while we are still computing that result. Because of this we continously recompute the
+ /// cycle until the result of the previous iteration is equal to the final result, at which
+ /// point we are done.
+ ///
+ /// This function returns `true` if we were able to finalize the goal and `false` if it has
+ /// updated the provisional cache and we have to recompute the current goal.
+ ///
+ /// FIXME: Refer to the rustc-dev-guide entry once it exists.
+ pub(super) fn try_finalize_goal(
+ &mut self,
+ actual_goal: CanonicalGoal<'tcx>,
+ response: QueryResult<'tcx>,
+ ) -> bool {
+ let cache = &mut self.provisional_cache;
+ let StackElem { goal, has_been_used } = cache.stack.pop().unwrap();
+ assert_eq!(goal, actual_goal);
+
+ let provisional_entry = cache.entries.get_mut(&goal).unwrap();
+ // Check whether the current stack entry is the root of a cycle.
+ //
+ // If so, we either move all participants of that cycle to the global cache
+ // or, in case the provisional response used in the cycle is not equal to the
+ // final response, have to recompute the goal after updating the provisional
+ // response to the final response of this iteration.
+ if has_been_used {
+ if provisional_entry.response == response {
+ // We simply drop all entries according to an immutable condition, so
+ // query instability is not a concern here.
+ #[allow(rustc::potential_query_instability)]
+ cache.entries.retain(|goal, entry| match entry.depth.cmp(&cache.stack.len()) {
+ Ordering::Less => true,
+ Ordering::Equal => {
+ Self::try_move_finished_goal_to_global_cache(
+ self.tcx,
+ &mut self.overflow_data,
+ &cache.stack,
+ // FIXME: these should be `Copy` :(
+ goal.clone(),
+ entry.response.clone(),
+ );
+ false
+ }
+ Ordering::Greater => bug!("entry with greater depth than the current leaf"),
+ });
+
+ true
+ } else {
+ provisional_entry.response = response;
+ cache.stack.push(StackElem { goal, has_been_used: false });
+ false
+ }
+ } else {
+ Self::try_move_finished_goal_to_global_cache(
+ self.tcx,
+ &mut self.overflow_data,
+ &cache.stack,
+ goal,
+ response,
+ );
+ cache.entries.remove(&goal);
+ true
+ }
+ }
+
+ fn try_move_finished_goal_to_global_cache(
+ tcx: TyCtxt<'tcx>,
+ overflow_data: &mut OverflowData,
+ stack: &[StackElem<'tcx>],
+ goal: CanonicalGoal<'tcx>,
+ response: QueryResult<'tcx>,
+ ) {
+ // We move goals to the global cache if we either did not hit an overflow or if it's
+ // the root goal as that will now always hit the same overflow limit.
+ //
+ // NOTE: We cannot move any non-root goals to the global cache even if their final result
+ // isn't impacted by the overflow as that goal still has unstable query dependencies
+ // because it didn't go its full depth.
+ //
+ // FIXME(@lcnr): We could still cache subtrees which are not impacted by overflow though.
+ // Tracking that info correctly isn't trivial, so I haven't implemented it for now.
+ let should_cache_globally = !overflow_data.did_overflow() || stack.is_empty();
+ if should_cache_globally {
+ // FIXME: move the provisional entry to the global cache.
+ let _ = (tcx, goal, response);
+ }
+ }
+}
+
+fn fixme_response_yes_no_constraints<'tcx>() -> QueryResult<'tcx> {
+ unimplemented!()
+}
+
+fn fixme_response_maybe_no_constraints<'tcx>() -> QueryResult<'tcx> {
+ unimplemented!()
+}
--- /dev/null
+use std::mem;
+
+use rustc_data_structures::fx::FxHashMap;
+use rustc_infer::{
+ infer::InferCtxt,
+ traits::{query::NoSolution, FulfillmentError, PredicateObligation, TraitEngine},
+};
+use rustc_middle::ty;
+
+use super::{Certainty, EvalCtxt};
+
+/// A trait engine using the new trait solver.
+///
+/// This is mostly identical to how `evaluate_all` works inside of the
+/// solver, except that the requirements are slightly different.
+///
+/// Unlike `evaluate_all` it is possible to add new obligations later on
+/// and we also have to track diagnostics information by using `Obligation`
+/// instead of `Goal`.
+///
+/// It is also likely that we want to use slightly different datastructures
+/// here as this will have to deal with far more root goals than `evaluate_all`.
+pub struct FulfillmentCtxt<'tcx> {
+ obligations: Vec<PredicateObligation<'tcx>>,
+}
+
+impl<'tcx> FulfillmentCtxt<'tcx> {
+ pub fn new() -> FulfillmentCtxt<'tcx> {
+ FulfillmentCtxt { obligations: Vec::new() }
+ }
+}
+
+impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
+ fn register_predicate_obligation(
+ &mut self,
+ _infcx: &InferCtxt<'tcx>,
+ obligation: PredicateObligation<'tcx>,
+ ) {
+ self.obligations.push(obligation);
+ }
+
+ fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
+ let errors = self.select_where_possible(infcx);
+ if !errors.is_empty() {
+ return errors;
+ }
+
+ if self.obligations.is_empty() {
+ Vec::new()
+ } else {
+ unimplemented!("ambiguous obligations")
+ }
+ }
+
+ fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
+ let errors = Vec::new();
+ for i in 0.. {
+ if !infcx.tcx.recursion_limit().value_within_limit(i) {
+ unimplemented!("overflow")
+ }
+
+ let mut has_changed = false;
+ for o in mem::take(&mut self.obligations) {
+ let mut cx = EvalCtxt::new(infcx.tcx);
+ let (changed, certainty) = match cx.evaluate_goal(infcx, o.clone().into()) {
+ Ok(result) => result,
+ Err(NoSolution) => unimplemented!("error"),
+ };
+
+ has_changed |= changed;
+ match certainty {
+ Certainty::Yes => {}
+ Certainty::Maybe(_) => self.obligations.push(o),
+ }
+ }
+
+ if !has_changed {
+ break;
+ }
+ }
+
+ errors
+ }
+
+ fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
+ self.obligations.clone()
+ }
+
+ fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> {
+ unimplemented!("Should be moved out of `TraitEngine`")
+ }
+}
--- /dev/null
+use rustc_infer::infer::canonical::CanonicalVarValues;
+use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc_infer::infer::InferCtxt;
+use rustc_infer::traits::query::NoSolution;
+use rustc_middle::ty::Ty;
+use rustc_span::DUMMY_SP;
+
+use crate::solve::ExternalConstraints;
+
+use super::{Certainty, QueryResult, Response};
+
+/// Methods used inside of the canonical queries of the solver.
+pub(super) trait InferCtxtExt<'tcx> {
+ fn next_ty_infer(&self) -> Ty<'tcx>;
+
+ fn make_canonical_response(
+ &self,
+ var_values: CanonicalVarValues<'tcx>,
+ certainty: Certainty,
+ ) -> QueryResult<'tcx>;
+}
+
+impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
+ fn next_ty_infer(&self) -> Ty<'tcx> {
+ self.next_ty_var(TypeVariableOrigin {
+ kind: TypeVariableOriginKind::MiscVariable,
+ span: DUMMY_SP,
+ })
+ }
+
+ fn make_canonical_response(
+ &self,
+ var_values: CanonicalVarValues<'tcx>,
+ certainty: Certainty,
+ ) -> QueryResult<'tcx> {
+ let external_constraints = take_external_constraints(self)?;
+
+ Ok(self.canonicalize_response(Response { var_values, external_constraints, certainty }))
+ }
+}
+
+#[instrument(level = "debug", skip(infcx), ret)]
+fn take_external_constraints<'tcx>(
+ infcx: &InferCtxt<'tcx>,
+) -> Result<ExternalConstraints<'tcx>, NoSolution> {
+ let region_obligations = infcx.take_registered_region_obligations();
+ let opaque_types = infcx.take_opaque_types_for_query_response();
+ Ok(ExternalConstraints {
+ // FIXME: Now that's definitely wrong :)
+ //
+ // Should also do the leak check here I think
+ regions: drop(region_obligations),
+ opaque_types,
+ })
+}
--- /dev/null
+//! The new trait solver, currently still WIP.
+//!
+//! As a user of the trait system, you can use `TyCtxt::evaluate_goal` to
+//! interact with this solver.
+//!
+//! For a high-level overview of how this solver works, check out the relevant
+//! section of the rustc-dev-guide.
+//!
+//! FIXME(@lcnr): Write that section. If you read this before then ask me
+//! about it on zulip.
+
+// FIXME: Instead of using `infcx.canonicalize_query` we have to add a new routine which
+// preserves universes and creates a unique var (in the highest universe) for each
+// appearance of a region.
+
+// FIXME: `CanonicalVarValues` should be interned and `Copy`.
+
+// FIXME: uses of `infcx.at` need to enable deferred projection equality once that's implemented.
+
+use std::mem;
+
+use rustc_infer::infer::canonical::OriginalQueryValues;
+use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::Obligation;
+use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
+use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{RegionOutlivesPredicate, ToPredicate, TypeOutlivesPredicate};
+use rustc_span::DUMMY_SP;
+
+use self::infcx_ext::InferCtxtExt;
+
+mod cache;
+mod fulfill;
+mod infcx_ext;
+mod overflow;
+mod project_goals;
+mod trait_goals;
+
+pub use fulfill::FulfillmentCtxt;
+
+/// A goal is a statement, i.e. `predicate`, we want to prove
+/// given some assumptions, i.e. `param_env`.
+///
+/// Most of the time the `param_env` contains the `where`-bounds of the function
+/// we're currently typechecking while the `predicate` is some trait bound.
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
+pub struct Goal<'tcx, P> {
+ param_env: ty::ParamEnv<'tcx>,
+ predicate: P,
+}
+
+impl<'tcx, P> Goal<'tcx, P> {
+ pub fn new(
+ tcx: TyCtxt<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
+ predicate: impl ToPredicate<'tcx, P>,
+ ) -> Goal<'tcx, P> {
+ Goal { param_env, predicate: predicate.to_predicate(tcx) }
+ }
+
+ /// Updates the goal to one with a different `predicate` but the same `param_env`.
+ fn with<Q>(self, tcx: TyCtxt<'tcx>, predicate: impl ToPredicate<'tcx, Q>) -> Goal<'tcx, Q> {
+ Goal { param_env: self.param_env, predicate: predicate.to_predicate(tcx) }
+ }
+}
+
+impl<'tcx, P> From<Obligation<'tcx, P>> for Goal<'tcx, P> {
+ fn from(obligation: Obligation<'tcx, P>) -> Goal<'tcx, P> {
+ Goal { param_env: obligation.param_env, predicate: obligation.predicate }
+ }
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Hash, TypeFoldable, TypeVisitable)]
+pub struct Response<'tcx> {
+ pub var_values: CanonicalVarValues<'tcx>,
+ /// Additional constraints returned by this query.
+ pub external_constraints: ExternalConstraints<'tcx>,
+ pub certainty: Certainty,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
+pub enum Certainty {
+ Yes,
+ Maybe(MaybeCause),
+}
+
+impl Certainty {
+ /// When proving multiple goals using **AND**, e.g. nested obligations for an impl,
+ /// use this function to unify the certainty of these goals
+ pub fn unify_and(self, other: Certainty) -> Certainty {
+ match (self, other) {
+ (Certainty::Yes, Certainty::Yes) => Certainty::Yes,
+ (Certainty::Yes, Certainty::Maybe(_)) => other,
+ (Certainty::Maybe(_), Certainty::Yes) => self,
+ (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Overflow)) => {
+ Certainty::Maybe(MaybeCause::Overflow)
+ }
+ // If at least one of the goals is ambiguous, hide the overflow as the ambiguous goal
+ // may still result in failure.
+ (Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(_))
+ | (Certainty::Maybe(_), Certainty::Maybe(MaybeCause::Ambiguity)) => {
+ Certainty::Maybe(MaybeCause::Ambiguity)
+ }
+ }
+ }
+}
+
+/// Why we failed to evaluate a goal.
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
+pub enum MaybeCause {
+ /// We failed due to ambiguity. This ambiguity can either
+ /// be a true ambiguity, i.e. there are multiple different answers,
+ /// or we hit a case where we just don't bother, e.g. `?x: Trait` goals.
+ Ambiguity,
+ /// We gave up due to an overflow, most often by hitting the recursion limit.
+ Overflow,
+}
+
+/// Additional constraints returned on success.
+#[derive(Debug, PartialEq, Eq, Clone, Hash, TypeFoldable, TypeVisitable)]
+pub struct ExternalConstraints<'tcx> {
+ // FIXME: implement this.
+ regions: (),
+ opaque_types: Vec<(Ty<'tcx>, Ty<'tcx>)>,
+}
+
+type CanonicalGoal<'tcx, T = ty::Predicate<'tcx>> = Canonical<'tcx, Goal<'tcx, T>>;
+type CanonicalResponse<'tcx> = Canonical<'tcx, Response<'tcx>>;
+/// The result of evaluating a canonical query.
+///
+/// FIXME: We use a different type than the existing canonical queries. This is because
+/// we need to add a `Certainty` for `overflow` and may want to restructure this code without
+/// having to worry about changes to currently used code. Once we've made progress on this
+/// solver, merge the two responses again.
+pub type QueryResult<'tcx> = Result<CanonicalResponse<'tcx>, NoSolution>;
+
+pub trait TyCtxtExt<'tcx> {
+ fn evaluate_goal(self, goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx>;
+}
+
+impl<'tcx> TyCtxtExt<'tcx> for TyCtxt<'tcx> {
+ fn evaluate_goal(self, goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx> {
+ let mut cx = EvalCtxt::new(self);
+ cx.evaluate_canonical_goal(goal)
+ }
+}
+
+struct EvalCtxt<'tcx> {
+ tcx: TyCtxt<'tcx>,
+
+ provisional_cache: cache::ProvisionalCache<'tcx>,
+ overflow_data: overflow::OverflowData,
+}
+
+impl<'tcx> EvalCtxt<'tcx> {
+ fn new(tcx: TyCtxt<'tcx>) -> EvalCtxt<'tcx> {
+ EvalCtxt {
+ tcx,
+ provisional_cache: cache::ProvisionalCache::empty(),
+ overflow_data: overflow::OverflowData::new(tcx),
+ }
+ }
+
+ /// Recursively evaluates `goal`, returning whether any inference vars have
+ /// been constrained and the certainty of the result.
+ fn evaluate_goal(
+ &mut self,
+ infcx: &InferCtxt<'tcx>,
+ goal: Goal<'tcx, ty::Predicate<'tcx>>,
+ ) -> Result<(bool, Certainty), NoSolution> {
+ let mut orig_values = OriginalQueryValues::default();
+ let canonical_goal = infcx.canonicalize_query(goal, &mut orig_values);
+ let canonical_response = self.evaluate_canonical_goal(canonical_goal)?;
+ Ok((
+ true, // FIXME: check whether `var_values` are an identity substitution.
+ fixme_instantiate_canonical_query_response(infcx, &orig_values, canonical_response),
+ ))
+ }
+
+ fn evaluate_canonical_goal(&mut self, goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx> {
+ match self.try_push_stack(goal) {
+ Ok(()) => {}
+ // Our goal is already on the stack, eager return.
+ Err(response) => return response,
+ }
+
+ // We may have to repeatedly recompute the goal in case of coinductive cycles,
+ // check out the `cache` module for more information.
+ //
+ // FIXME: Similar to `evaluate_all`, this has to check for overflow.
+ loop {
+ let result = self.compute_goal(goal);
+
+ // FIXME: `Response` should be `Copy`
+ if self.try_finalize_goal(goal, result.clone()) {
+ return result;
+ }
+ }
+ }
+
+ fn compute_goal(&mut self, canonical_goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx> {
+ // WARNING: We're looking at a canonical value without instantiating it here.
+ //
+ // We have to be incredibly careful to not change the order of bound variables or
+ // remove any. As we go from `Goal<'tcx, Predicate>` to `Goal` with the variants
+ // of `PredicateKind` this is the case and it is and faster than instantiating and
+ // recanonicalizing.
+ let Goal { param_env, predicate } = canonical_goal.value;
+ if let Some(kind) = predicate.kind().no_bound_vars() {
+ match kind {
+ ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => self.compute_trait_goal(
+ canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
+ ),
+ ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => self
+ .compute_projection_goal(
+ canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
+ ),
+ ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => self
+ .compute_type_outlives_goal(
+ canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
+ ),
+ ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => self
+ .compute_region_outlives_goal(
+ canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
+ ),
+ // FIXME: implement these predicates :)
+ ty::PredicateKind::WellFormed(_)
+ | ty::PredicateKind::ObjectSafe(_)
+ | ty::PredicateKind::ClosureKind(_, _, _)
+ | ty::PredicateKind::Subtype(_)
+ | ty::PredicateKind::Coerce(_)
+ | ty::PredicateKind::ConstEvaluatable(_)
+ | ty::PredicateKind::ConstEquate(_, _)
+ | ty::PredicateKind::TypeWellFormedFromEnv(_)
+ | ty::PredicateKind::Ambiguous => unimplemented!(),
+ }
+ } else {
+ let (infcx, goal, var_values) =
+ self.tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical_goal);
+ let kind = infcx.replace_bound_vars_with_placeholders(goal.predicate.kind());
+ let goal = goal.with(self.tcx, ty::Binder::dummy(kind));
+ let (_, certainty) = self.evaluate_goal(&infcx, goal)?;
+ infcx.make_canonical_response(var_values, certainty)
+ }
+ }
+
+ fn compute_type_outlives_goal(
+ &mut self,
+ _goal: CanonicalGoal<'tcx, TypeOutlivesPredicate<'tcx>>,
+ ) -> QueryResult<'tcx> {
+ todo!()
+ }
+
+ fn compute_region_outlives_goal(
+ &mut self,
+ _goal: CanonicalGoal<'tcx, RegionOutlivesPredicate<'tcx>>,
+ ) -> QueryResult<'tcx> {
+ todo!()
+ }
+}
+
+impl<'tcx> EvalCtxt<'tcx> {
+ fn evaluate_all(
+ &mut self,
+ infcx: &InferCtxt<'tcx>,
+ mut goals: Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
+ ) -> Result<Certainty, NoSolution> {
+ let mut new_goals = Vec::new();
+ self.repeat_while_none(|this| {
+ let mut has_changed = Err(Certainty::Yes);
+ for goal in goals.drain(..) {
+ let (changed, certainty) = match this.evaluate_goal(infcx, goal) {
+ Ok(result) => result,
+ Err(NoSolution) => return Some(Err(NoSolution)),
+ };
+
+ if changed {
+ has_changed = Ok(());
+ }
+
+ match certainty {
+ Certainty::Yes => {}
+ Certainty::Maybe(_) => {
+ new_goals.push(goal);
+ has_changed = has_changed.map_err(|c| c.unify_and(certainty));
+ }
+ }
+ }
+
+ match has_changed {
+ Ok(()) => {
+ mem::swap(&mut new_goals, &mut goals);
+ None
+ }
+ Err(certainty) => Some(Ok(certainty)),
+ }
+ })
+ }
+}
+
+fn fixme_instantiate_canonical_query_response<'tcx>(
+ _: &InferCtxt<'tcx>,
+ _: &OriginalQueryValues<'tcx>,
+ _: CanonicalResponse<'tcx>,
+) -> Certainty {
+ unimplemented!()
+}
--- /dev/null
+use rustc_infer::traits::query::NoSolution;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::Limit;
+
+use super::{Certainty, EvalCtxt, MaybeCause, QueryResult};
+
+/// When detecting a solver overflow, we return ambiguity. Overflow can be
+/// *hidden* by either a fatal error in an **AND** or a trivial success in an **OR**.
+///
+/// This is in issue in case of exponential blowup, e.g. if each goal on the stack
+/// has multiple nested (overflowing) candidates. To deal with this, we reduce the limit
+/// used by the solver when hitting the default limit for the first time.
+///
+/// FIXME: Get tests where always using the `default_limit` results in a hang and refer
+/// to them here. We can also improve the overflow strategy if necessary.
+pub(super) struct OverflowData {
+ default_limit: Limit,
+ current_limit: Limit,
+ /// When proving an **AND** we have to repeatedly iterate over the yet unproven goals.
+ ///
+ /// Because of this each iteration also increases the depth in addition to the stack
+ /// depth.
+ additional_depth: usize,
+}
+
+impl OverflowData {
+ pub(super) fn new(tcx: TyCtxt<'_>) -> OverflowData {
+ let default_limit = tcx.recursion_limit();
+ OverflowData { default_limit, current_limit: default_limit, additional_depth: 0 }
+ }
+
+ #[inline]
+ pub(super) fn did_overflow(&self) -> bool {
+ self.default_limit.0 != self.current_limit.0
+ }
+
+ #[inline]
+ pub(super) fn has_overflow(&self, depth: usize) -> bool {
+ self.current_limit.value_within_limit(depth + self.additional_depth)
+ }
+
+ /// Updating the current limit when hitting overflow.
+ fn deal_with_overflow(&mut self) {
+ // When first hitting overflow we reduce the overflow limit
+ // for all future goals to prevent hangs if there's an exponental
+ // blowup.
+ self.current_limit.0 = self.default_limit.0 / 8;
+ }
+}
+
+impl<'tcx> EvalCtxt<'tcx> {
+ pub(super) fn deal_with_overflow(&mut self) -> QueryResult<'tcx> {
+ self.overflow_data.deal_with_overflow();
+ fixme_response_overflow_no_constraints()
+ }
+
+ /// A `while`-loop which tracks overflow.
+ pub(super) fn repeat_while_none(
+ &mut self,
+ mut loop_body: impl FnMut(&mut Self) -> Option<Result<Certainty, NoSolution>>,
+ ) -> Result<Certainty, NoSolution> {
+ let start_depth = self.overflow_data.additional_depth;
+ let depth = self.provisional_cache.current_depth();
+ while !self.overflow_data.has_overflow(depth) {
+ if let Some(result) = loop_body(self) {
+ self.overflow_data.additional_depth = start_depth;
+ return result;
+ }
+
+ self.overflow_data.additional_depth += 1;
+ }
+ self.overflow_data.additional_depth = start_depth;
+ self.overflow_data.deal_with_overflow();
+ Ok(Certainty::Maybe(MaybeCause::Overflow))
+ }
+}
+
+fn fixme_response_overflow_no_constraints<'tcx>() -> QueryResult<'tcx> {
+ unimplemented!()
+}
--- /dev/null
+use crate::traits::{specialization_graph, translate_substs};
+
+use super::infcx_ext::InferCtxtExt;
+use super::{
+ fixme_instantiate_canonical_query_response, CanonicalGoal, CanonicalResponse, Certainty,
+ EvalCtxt, Goal, QueryResult,
+};
+use rustc_errors::ErrorGuaranteed;
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::DefId;
+use rustc_infer::infer::canonical::{CanonicalVarValues, OriginalQueryValues};
+use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
+use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::specialization_graph::LeafDef;
+use rustc_infer::traits::{ObligationCause, Reveal};
+use rustc_middle::ty;
+use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
+use rustc_middle::ty::ProjectionPredicate;
+use rustc_middle::ty::TypeVisitable;
+use rustc_span::DUMMY_SP;
+use std::iter;
+
+// FIXME: Deduplicate the candidate code between projection and trait goal.
+
+/// Similar to [super::trait_goals::Candidate] but for `Projection` goals.
+#[derive(Debug, Clone)]
+struct Candidate<'tcx> {
+ source: CandidateSource,
+ result: CanonicalResponse<'tcx>,
+}
+
+#[allow(dead_code)] // FIXME: implement and use all variants.
+#[derive(Debug, Clone, Copy)]
+enum CandidateSource {
+ Impl(DefId),
+ ParamEnv(usize),
+ Builtin,
+}
+
+impl<'tcx> EvalCtxt<'tcx> {
+ pub(super) fn compute_projection_goal(
+ &mut self,
+ goal: CanonicalGoal<'tcx, ProjectionPredicate<'tcx>>,
+ ) -> QueryResult<'tcx> {
+ let candidates = self.assemble_and_evaluate_project_candidates(goal);
+ self.merge_project_candidates(candidates)
+ }
+
+ fn assemble_and_evaluate_project_candidates(
+ &mut self,
+ goal: CanonicalGoal<'tcx, ProjectionPredicate<'tcx>>,
+ ) -> Vec<Candidate<'tcx>> {
+ let (ref infcx, goal, var_values) =
+ self.tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
+ let mut acx = AssemblyCtxt { cx: self, infcx, var_values, candidates: Vec::new() };
+
+ acx.assemble_candidates_after_normalizing_self_ty(goal);
+ acx.assemble_impl_candidates(goal);
+ acx.candidates
+ }
+
+ fn merge_project_candidates(
+ &mut self,
+ mut candidates: Vec<Candidate<'tcx>>,
+ ) -> QueryResult<'tcx> {
+ match candidates.len() {
+ 0 => return Err(NoSolution),
+ 1 => return Ok(candidates.pop().unwrap().result),
+ _ => {}
+ }
+
+ if candidates.len() > 1 {
+ let mut i = 0;
+ 'outer: while i < candidates.len() {
+ for j in (0..candidates.len()).filter(|&j| i != j) {
+ if self.project_candidate_should_be_dropped_in_favor_of(
+ &candidates[i],
+ &candidates[j],
+ ) {
+ debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
+ candidates.swap_remove(i);
+ continue 'outer;
+ }
+ }
+
+ debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
+ // If there are *STILL* multiple candidates, give up
+ // and report ambiguity.
+ i += 1;
+ if i > 1 {
+ debug!("multiple matches, ambig");
+ // FIXME: return overflow if all candidates overflow, otherwise return ambiguity.
+ unimplemented!();
+ }
+ }
+ }
+
+ Ok(candidates.pop().unwrap().result)
+ }
+
+ fn project_candidate_should_be_dropped_in_favor_of(
+ &self,
+ candidate: &Candidate<'tcx>,
+ other: &Candidate<'tcx>,
+ ) -> bool {
+ // FIXME: implement this
+ match (candidate.source, other.source) {
+ (CandidateSource::Impl(_), _)
+ | (CandidateSource::ParamEnv(_), _)
+ | (CandidateSource::Builtin, _) => unimplemented!(),
+ }
+ }
+}
+
+/// Similar to [super::trait_goals::AssemblyCtxt] but for `Projection` goals.
+struct AssemblyCtxt<'a, 'tcx> {
+ cx: &'a mut EvalCtxt<'tcx>,
+ infcx: &'a InferCtxt<'tcx>,
+ var_values: CanonicalVarValues<'tcx>,
+ candidates: Vec<Candidate<'tcx>>,
+}
+
+impl<'tcx> AssemblyCtxt<'_, 'tcx> {
+ fn try_insert_candidate(&mut self, source: CandidateSource, certainty: Certainty) {
+ match self.infcx.make_canonical_response(self.var_values.clone(), certainty) {
+ Ok(result) => self.candidates.push(Candidate { source, result }),
+ Err(NoSolution) => debug!(?source, ?certainty, "failed leakcheck"),
+ }
+ }
+
+ fn assemble_candidates_after_normalizing_self_ty(
+ &mut self,
+ goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
+ ) {
+ let tcx = self.cx.tcx;
+ let &ty::Alias(ty::Projection, projection_ty) = goal.predicate.projection_ty.self_ty().kind() else {
+ return
+ };
+ self.infcx.probe(|_| {
+ let normalized_ty = self.infcx.next_ty_infer();
+ let normalizes_to_goal = goal.with(
+ tcx,
+ ty::Binder::dummy(ty::ProjectionPredicate {
+ projection_ty,
+ term: normalized_ty.into(),
+ }),
+ );
+ let normalization_certainty =
+ match self.cx.evaluate_goal(&self.infcx, normalizes_to_goal) {
+ Ok((_, certainty)) => certainty,
+ Err(NoSolution) => return,
+ };
+
+ // NOTE: Alternatively we could call `evaluate_goal` here and only have a `Normalized` candidate.
+ // This doesn't work as long as we use `CandidateSource` in both winnowing and to resolve associated items.
+ let goal = goal.with(tcx, goal.predicate.with_self_ty(tcx, normalized_ty));
+ let mut orig_values = OriginalQueryValues::default();
+ let goal = self.infcx.canonicalize_query(goal, &mut orig_values);
+ let normalized_candidates = self.cx.assemble_and_evaluate_project_candidates(goal);
+ // Map each candidate from being canonical wrt the current inference context to being
+ // canonical wrt the caller.
+ for Candidate { source, result } in normalized_candidates {
+ self.infcx.probe(|_| {
+ let candidate_certainty = fixme_instantiate_canonical_query_response(
+ self.infcx,
+ &orig_values,
+ result,
+ );
+ self.try_insert_candidate(
+ source,
+ normalization_certainty.unify_and(candidate_certainty),
+ )
+ })
+ }
+ })
+ }
+
+ fn assemble_impl_candidates(&mut self, goal: Goal<'tcx, ProjectionPredicate<'tcx>>) {
+ self.cx.tcx.for_each_relevant_impl(
+ goal.predicate.trait_def_id(self.cx.tcx),
+ goal.predicate.self_ty(),
+ |impl_def_id| self.consider_impl_candidate(goal, impl_def_id),
+ );
+ }
+
+ fn consider_impl_candidate(
+ &mut self,
+ goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
+ impl_def_id: DefId,
+ ) {
+ let tcx = self.cx.tcx;
+ let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
+ let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap();
+ let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
+ if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
+ .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
+ {
+ return;
+ }
+
+ self.infcx.probe(|_| {
+ let impl_substs = self.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
+ let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
+
+ let Ok(InferOk { obligations, .. }) = self
+ .infcx
+ .at(&ObligationCause::dummy(), goal.param_env)
+ .define_opaque_types(false)
+ .eq(goal_trait_ref, impl_trait_ref)
+ .map_err(|e| debug!("failed to equate trait refs: {e:?}"))
+ else {
+ return
+ };
+
+ let nested_goals = obligations.into_iter().map(|o| o.into()).collect();
+ let Ok(trait_ref_certainty) = self.cx.evaluate_all(self.infcx, nested_goals) else { return };
+
+ let Some(assoc_def) = self.fetch_eligible_assoc_item_def(
+ goal.param_env,
+ goal_trait_ref,
+ goal.predicate.def_id(),
+ impl_def_id
+ ) else {
+ return
+ };
+
+ if !assoc_def.item.defaultness(tcx).has_value() {
+ tcx.sess.delay_span_bug(
+ tcx.def_span(assoc_def.item.def_id),
+ "missing value for assoc item in impl",
+ );
+ }
+
+ // Getting the right substitutions here is complex, e.g. given:
+ // - a goal `<Vec<u32> as Trait<i32>>::Assoc<u64>`
+ // - the applicable impl `impl<T> Trait<i32> for Vec<T>`
+ // - and the impl which defines `Assoc` being `impl<T, U> Trait<U> for Vec<T>`
+ //
+ // We first rebase the goal substs onto the impl, going from `[Vec<u32>, i32, u64]`
+ // to `[u32, u64]`.
+ //
+ // And then map these substs to the substs of the defining impl of `Assoc`, going
+ // from `[u32, u64]` to `[u32, i32, u64]`.
+ let impl_substs_with_gat = goal.predicate.projection_ty.substs.rebase_onto(
+ tcx,
+ goal_trait_ref.def_id,
+ impl_trait_ref.substs,
+ );
+ let substs = translate_substs(
+ self.infcx,
+ goal.param_env,
+ impl_def_id,
+ impl_substs_with_gat,
+ assoc_def.defining_node,
+ );
+
+ // Finally we construct the actual value of the associated type.
+ let is_const = matches!(tcx.def_kind(assoc_def.item.def_id), DefKind::AssocConst);
+ let ty = tcx.bound_type_of(assoc_def.item.def_id);
+ let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const {
+ let identity_substs = ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id);
+ let did = ty::WithOptConstParam::unknown(assoc_def.item.def_id);
+ let kind =
+ ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs));
+ ty.map_bound(|ty| tcx.mk_const(kind, ty).into())
+ } else {
+ ty.map_bound(|ty| ty.into())
+ };
+
+ let Ok(InferOk { obligations, .. }) = self
+ .infcx
+ .at(&ObligationCause::dummy(), goal.param_env)
+ .define_opaque_types(false)
+ .eq(goal.predicate.term, term.subst(tcx, substs))
+ .map_err(|e| debug!("failed to equate trait refs: {e:?}"))
+ else {
+ return
+ };
+
+ let nested_goals = obligations.into_iter().map(|o| o.into()).collect();
+ let Ok(rhs_certainty) = self.cx.evaluate_all(self.infcx, nested_goals) else { return };
+
+ let certainty = trait_ref_certainty.unify_and(rhs_certainty);
+ self.try_insert_candidate(CandidateSource::Impl(impl_def_id), certainty);
+ })
+ }
+
+ /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.
+ ///
+ /// FIXME: We should merge these 3 implementations as it's likely that they otherwise
+ /// diverge.
+ #[instrument(level = "debug", skip(self, param_env), ret)]
+ fn fetch_eligible_assoc_item_def(
+ &self,
+ param_env: ty::ParamEnv<'tcx>,
+ goal_trait_ref: ty::TraitRef<'tcx>,
+ trait_assoc_def_id: DefId,
+ impl_def_id: DefId,
+ ) -> Option<LeafDef> {
+ let node_item =
+ specialization_graph::assoc_def(self.cx.tcx, impl_def_id, trait_assoc_def_id)
+ .map_err(|ErrorGuaranteed { .. }| ())
+ .ok()?;
+
+ let eligible = if node_item.is_final() {
+ // Non-specializable items are always projectable.
+ true
+ } else {
+ // Only reveal a specializable default if we're past type-checking
+ // and the obligation is monomorphic, otherwise passes such as
+ // transmute checking and polymorphic MIR optimizations could
+ // get a result which isn't correct for all monomorphizations.
+ if param_env.reveal() == Reveal::All {
+ let poly_trait_ref = self.infcx.resolve_vars_if_possible(goal_trait_ref);
+ !poly_trait_ref.still_further_specializable()
+ } else {
+ debug!(?node_item.item.def_id, "not eligible due to default");
+ false
+ }
+ };
+
+ if eligible { Some(node_item) } else { None }
+ }
+}
--- /dev/null
+//! Dealing with trait goals, i.e. `T: Trait<'a, U>`.
+
+use std::iter;
+
+use super::infcx_ext::InferCtxtExt;
+use super::{
+ fixme_instantiate_canonical_query_response, CanonicalGoal, CanonicalResponse, Certainty,
+ EvalCtxt, Goal, QueryResult,
+};
+use rustc_hir::def_id::DefId;
+use rustc_infer::infer::canonical::{CanonicalVarValues, OriginalQueryValues};
+use rustc_infer::infer::TyCtxtInferExt;
+use rustc_infer::infer::{InferCtxt, InferOk};
+use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::ObligationCause;
+use rustc_middle::ty;
+use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
+use rustc_middle::ty::TraitPredicate;
+use rustc_span::DUMMY_SP;
+
+/// A candidate is a possible way to prove a goal.
+///
+/// It consists of both the `source`, which describes how that goal
+/// would be proven, and the `result` when using the given `source`.
+///
+/// For the list of possible candidates, please look at the documentation
+/// of [CandidateSource].
+#[derive(Debug, Clone)]
+pub(super) struct Candidate<'tcx> {
+ source: CandidateSource,
+ result: CanonicalResponse<'tcx>,
+}
+
+#[allow(dead_code)] // FIXME: implement and use all variants.
+#[derive(Debug, Clone, Copy)]
+pub(super) enum CandidateSource {
+ /// Some user-defined impl with the given `DefId`.
+ Impl(DefId),
+ /// The n-th caller bound in the `param_env` of our goal.
+ ///
+ /// This is pretty much always a bound from the `where`-clauses of the
+ /// currently checked item.
+ ParamEnv(usize),
+ /// A bound on the `self_ty` in case it is a projection or an opaque type.
+ ///
+ /// # Examples
+ ///
+ /// ```ignore (for syntax highlighting)
+ /// trait Trait {
+ /// type Assoc: OtherTrait;
+ /// }
+ /// ```
+ ///
+ /// We know that `<Whatever as Trait>::Assoc: OtherTrait` holds by looking at
+ /// the bounds on `Trait::Assoc`.
+ AliasBound(usize),
+ /// A builtin implementation for some specific traits, used in cases
+ /// where we cannot rely an ordinary library implementations.
+ ///
+ /// The most notable examples are `Sized`, `Copy` and `Clone`. This is also
+ /// used for the `DiscriminantKind` and `Pointee` trait, both of which have
+ /// an associated type.
+ Builtin,
+ /// An automatic impl for an auto trait, e.g. `Send`. These impls recursively look
+ /// at the constituent types of the `self_ty` to check whether the auto trait
+ /// is implemented for those.
+ AutoImpl,
+}
+
+struct AssemblyCtxt<'a, 'tcx> {
+ cx: &'a mut EvalCtxt<'tcx>,
+ infcx: &'a InferCtxt<'tcx>,
+ var_values: CanonicalVarValues<'tcx>,
+ candidates: Vec<Candidate<'tcx>>,
+}
+
+impl<'tcx> EvalCtxt<'tcx> {
+ pub(super) fn compute_trait_goal(
+ &mut self,
+ goal: CanonicalGoal<'tcx, TraitPredicate<'tcx>>,
+ ) -> QueryResult<'tcx> {
+ let candidates = self.assemble_and_evaluate_trait_candidates(goal);
+ self.merge_trait_candidates_discard_reservation_impls(candidates)
+ }
+
+ pub(super) fn assemble_and_evaluate_trait_candidates(
+ &mut self,
+ goal: CanonicalGoal<'tcx, TraitPredicate<'tcx>>,
+ ) -> Vec<Candidate<'tcx>> {
+ let (ref infcx, goal, var_values) =
+ self.tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
+ let mut acx = AssemblyCtxt { cx: self, infcx, var_values, candidates: Vec::new() };
+
+ acx.assemble_candidates_after_normalizing_self_ty(goal);
+ acx.assemble_impl_candidates(goal);
+
+ // FIXME: Remaining candidates
+ acx.candidates
+ }
+
+ #[instrument(level = "debug", skip(self), ret)]
+ pub(super) fn merge_trait_candidates_discard_reservation_impls(
+ &mut self,
+ mut candidates: Vec<Candidate<'tcx>>,
+ ) -> QueryResult<'tcx> {
+ match candidates.len() {
+ 0 => return Err(NoSolution),
+ 1 => return Ok(self.discard_reservation_impl(candidates.pop().unwrap()).result),
+ _ => {}
+ }
+
+ if candidates.len() > 1 {
+ let mut i = 0;
+ 'outer: while i < candidates.len() {
+ for j in (0..candidates.len()).filter(|&j| i != j) {
+ if self.trait_candidate_should_be_dropped_in_favor_of(
+ &candidates[i],
+ &candidates[j],
+ ) {
+ debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
+ candidates.swap_remove(i);
+ continue 'outer;
+ }
+ }
+
+ debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
+ // If there are *STILL* multiple candidates, give up
+ // and report ambiguity.
+ i += 1;
+ if i > 1 {
+ debug!("multiple matches, ambig");
+ // FIXME: return overflow if all candidates overflow, otherwise return ambiguity.
+ unimplemented!();
+ }
+ }
+ }
+
+ Ok(self.discard_reservation_impl(candidates.pop().unwrap()).result)
+ }
+
+ fn trait_candidate_should_be_dropped_in_favor_of(
+ &self,
+ candidate: &Candidate<'tcx>,
+ other: &Candidate<'tcx>,
+ ) -> bool {
+ // FIXME: implement this
+ match (candidate.source, other.source) {
+ (CandidateSource::Impl(_), _)
+ | (CandidateSource::ParamEnv(_), _)
+ | (CandidateSource::AliasBound(_), _)
+ | (CandidateSource::Builtin, _)
+ | (CandidateSource::AutoImpl, _) => unimplemented!(),
+ }
+ }
+
+ fn discard_reservation_impl(&self, candidate: Candidate<'tcx>) -> Candidate<'tcx> {
+ if let CandidateSource::Impl(def_id) = candidate.source {
+ if let ty::ImplPolarity::Reservation = self.tcx.impl_polarity(def_id) {
+ debug!("Selected reservation impl");
+ // FIXME: reduce candidate to ambiguous
+ // FIXME: replace `var_values` with identity, yeet external constraints.
+ unimplemented!()
+ }
+ }
+
+ candidate
+ }
+}
+
+impl<'tcx> AssemblyCtxt<'_, 'tcx> {
+ /// Adds a new candidate using the current state of the inference context.
+ ///
+ /// This does require each assembly method to correctly use `probe` to not taint
+ /// the results of other candidates.
+ fn try_insert_candidate(&mut self, source: CandidateSource, certainty: Certainty) {
+ match self.infcx.make_canonical_response(self.var_values.clone(), certainty) {
+ Ok(result) => self.candidates.push(Candidate { source, result }),
+ Err(NoSolution) => debug!(?source, ?certainty, "failed leakcheck"),
+ }
+ }
+
+ /// If the self type of a trait goal is a projection, computing the relevant candidates is difficult.
+ ///
+ /// To deal with this, we first try to normalize the self type and add the candidates for the normalized
+ /// self type to the list of candidates in case that succeeds. Note that we can't just eagerly return in
+ /// this case as projections as self types add `
+ fn assemble_candidates_after_normalizing_self_ty(
+ &mut self,
+ goal: Goal<'tcx, TraitPredicate<'tcx>>,
+ ) {
+ let tcx = self.cx.tcx;
+ // FIXME: We also have to normalize opaque types, not sure where to best fit that in.
+ let &ty::Alias(ty::Projection, projection_ty) = goal.predicate.self_ty().kind() else {
+ return
+ };
+ self.infcx.probe(|_| {
+ let normalized_ty = self.infcx.next_ty_infer();
+ let normalizes_to_goal = goal.with(
+ tcx,
+ ty::Binder::dummy(ty::ProjectionPredicate {
+ projection_ty,
+ term: normalized_ty.into(),
+ }),
+ );
+ let normalization_certainty =
+ match self.cx.evaluate_goal(&self.infcx, normalizes_to_goal) {
+ Ok((_, certainty)) => certainty,
+ Err(NoSolution) => return,
+ };
+
+ // NOTE: Alternatively we could call `evaluate_goal` here and only have a `Normalized` candidate.
+ // This doesn't work as long as we use `CandidateSource` in both winnowing and to resolve associated items.
+ let goal = goal.with(tcx, goal.predicate.with_self_type(tcx, normalized_ty));
+ let mut orig_values = OriginalQueryValues::default();
+ let goal = self.infcx.canonicalize_query(goal, &mut orig_values);
+ let normalized_candidates = self.cx.assemble_and_evaluate_trait_candidates(goal);
+
+ // Map each candidate from being canonical wrt the current inference context to being
+ // canonical wrt the caller.
+ for Candidate { source, result } in normalized_candidates {
+ self.infcx.probe(|_| {
+ let candidate_certainty = fixme_instantiate_canonical_query_response(
+ self.infcx,
+ &orig_values,
+ result,
+ );
+
+ // FIXME: This is a bit scary if the `normalizes_to_goal` overflows.
+ //
+ // If we have an ambiguous candidate it hides that normalization
+ // caused an overflow which may cause issues.
+ self.try_insert_candidate(
+ source,
+ normalization_certainty.unify_and(candidate_certainty),
+ )
+ })
+ }
+ })
+ }
+
+ fn assemble_impl_candidates(&mut self, goal: Goal<'tcx, TraitPredicate<'tcx>>) {
+ self.cx.tcx.for_each_relevant_impl(
+ goal.predicate.def_id(),
+ goal.predicate.self_ty(),
+ |impl_def_id| self.consider_impl_candidate(goal, impl_def_id),
+ );
+ }
+
+ fn consider_impl_candidate(
+ &mut self,
+ goal: Goal<'tcx, TraitPredicate<'tcx>>,
+ impl_def_id: DefId,
+ ) {
+ let impl_trait_ref = self.cx.tcx.bound_impl_trait_ref(impl_def_id).unwrap();
+ let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
+ if iter::zip(goal.predicate.trait_ref.substs, impl_trait_ref.skip_binder().substs)
+ .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
+ {
+ return;
+ }
+
+ self.infcx.probe(|_| {
+ let impl_substs = self.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
+ let impl_trait_ref = impl_trait_ref.subst(self.cx.tcx, impl_substs);
+
+ let Ok(InferOk { obligations, .. }) = self
+ .infcx
+ .at(&ObligationCause::dummy(), goal.param_env)
+ .define_opaque_types(false)
+ .eq(goal.predicate.trait_ref, impl_trait_ref)
+ .map_err(|e| debug!("failed to equate trait refs: {e:?}"))
+ else {
+ return
+ };
+
+ let nested_goals = obligations.into_iter().map(|o| o.into()).collect();
+
+ let Ok(certainty) = self.cx.evaluate_all(self.infcx, nested_goals) else { return };
+ self.try_insert_candidate(CandidateSource::Impl(impl_def_id), certainty);
+ })
+ }
+}
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::DefKind;
-use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_infer::infer::at::At;
use rustc_infer::infer::resolve::OpportunisticRegionResolver;
// NOTE: This should be kept in sync with the similar code in
// `rustc_ty_utils::instance::resolve_associated_item()`.
let node_item =
- assoc_def(selcx, impl_data.impl_def_id, obligation.predicate.def_id)
+ specialization_graph::assoc_def(selcx.tcx(), impl_data.impl_def_id, obligation.predicate.def_id)
.map_err(|ErrorGuaranteed { .. }| ())?;
if node_item.is_final() {
let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
let param_env = obligation.param_env;
- let Ok(assoc_ty) = assoc_def(selcx, impl_def_id, assoc_item_id) else {
+ let Ok(assoc_ty) = specialization_graph::assoc_def(tcx, impl_def_id, assoc_item_id) else {
return Progress { term: tcx.ty_error().into(), obligations: nested };
};
let mut obligations = data.nested;
let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.def_id);
- let Ok(leaf_def) = assoc_def(selcx, data.impl_def_id, trait_fn_def_id) else {
+ let Ok(leaf_def) = specialization_graph::assoc_def(tcx, data.impl_def_id, trait_fn_def_id) else {
return Progress { term: tcx.ty_error().into(), obligations };
};
if !leaf_def.item.defaultness(tcx).has_value() {
}
}
-/// Locate the definition of an associated type in the specialization hierarchy,
-/// starting from the given impl.
-///
-/// Based on the "projection mode", this lookup may in fact only examine the
-/// topmost impl. See the comments for `Reveal` for more details.
-fn assoc_def(
- selcx: &SelectionContext<'_, '_>,
- impl_def_id: DefId,
- assoc_def_id: DefId,
-) -> Result<specialization_graph::LeafDef, ErrorGuaranteed> {
- let tcx = selcx.tcx();
- let trait_def_id = tcx.impl_trait_ref(impl_def_id).unwrap().def_id;
- let trait_def = tcx.trait_def(trait_def_id);
-
- // This function may be called while we are still building the
- // specialization graph that is queried below (via TraitDef::ancestors()),
- // so, in order to avoid unnecessary infinite recursion, we manually look
- // for the associated item at the given impl.
- // If there is no such item in that impl, this function will fail with a
- // cycle error if the specialization graph is currently being built.
- if let Some(&impl_item_id) = tcx.impl_item_implementor_ids(impl_def_id).get(&assoc_def_id) {
- let item = tcx.associated_item(impl_item_id);
- let impl_node = specialization_graph::Node::Impl(impl_def_id);
- return Ok(specialization_graph::LeafDef {
- item: *item,
- defining_node: impl_node,
- finalizing_node: if item.defaultness(tcx).is_default() {
- None
- } else {
- Some(impl_node)
- },
- });
- }
-
- let ancestors = trait_def.ancestors(tcx, impl_def_id)?;
- if let Some(assoc_item) = ancestors.leaf_def(tcx, assoc_def_id) {
- Ok(assoc_item)
- } else {
- // This is saying that neither the trait nor
- // the impl contain a definition for this
- // associated type. Normally this situation
- // could only arise through a compiler bug --
- // if the user wrote a bad item name, it
- // should have failed in astconv.
- bug!(
- "No associated type `{}` for {}",
- tcx.item_name(assoc_def_id),
- tcx.def_path_str(impl_def_id)
- )
- }
-}
-
pub(crate) trait ProjectionCacheKeyExt<'cx, 'tcx>: Sized {
fn from_poly_projection_predicate(
selcx: &mut SelectionContext<'cx, 'tcx>,
where
I: Iterator<Item = ty::Predicate<'tcx>>,
{
- cycle.all(|predicate| self.coinductive_predicate(predicate))
- }
-
- fn coinductive_predicate(&self, predicate: ty::Predicate<'tcx>) -> bool {
- let result = match predicate.kind().skip_binder() {
- ty::PredicateKind::Clause(ty::Clause::Trait(ref data)) => {
- self.tcx().trait_is_coinductive(data.def_id())
- }
- ty::PredicateKind::WellFormed(_) => true,
- _ => false,
- };
- debug!(?predicate, ?result, "coinductive_predicate");
- result
+ cycle.all(|predicate| predicate.is_coinductive(self.tcx()))
}
/// Further evaluates `candidate` to decide whether all type parameters match and whether nested
use super::OverlapError;
use crate::traits;
+use rustc_errors::ErrorGuaranteed;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
self.children.entry(parent).or_default().insert_blindly(tcx, child);
}
}
+
+/// Locate the definition of an associated type in the specialization hierarchy,
+/// starting from the given impl.
+pub(crate) fn assoc_def(
+ tcx: TyCtxt<'_>,
+ impl_def_id: DefId,
+ assoc_def_id: DefId,
+) -> Result<LeafDef, ErrorGuaranteed> {
+ let trait_def_id = tcx.impl_trait_ref(impl_def_id).unwrap().def_id;
+ let trait_def = tcx.trait_def(trait_def_id);
+
+ // This function may be called while we are still building the
+ // specialization graph that is queried below (via TraitDef::ancestors()),
+ // so, in order to avoid unnecessary infinite recursion, we manually look
+ // for the associated item at the given impl.
+ // If there is no such item in that impl, this function will fail with a
+ // cycle error if the specialization graph is currently being built.
+ if let Some(&impl_item_id) = tcx.impl_item_implementor_ids(impl_def_id).get(&assoc_def_id) {
+ let &item = tcx.associated_item(impl_item_id);
+ let impl_node = Node::Impl(impl_def_id);
+ return Ok(LeafDef {
+ item,
+ defining_node: impl_node,
+ finalizing_node: if item.defaultness(tcx).is_default() {
+ None
+ } else {
+ Some(impl_node)
+ },
+ });
+ }
+
+ let ancestors = trait_def.ancestors(tcx, impl_def_id)?;
+ if let Some(assoc_item) = ancestors.leaf_def(tcx, assoc_def_id) {
+ Ok(assoc_item)
+ } else {
+ // This is saying that neither the trait nor
+ // the impl contain a definition for this
+ // associated type. Normally this situation
+ // could only arise through a compiler bug --
+ // if the user wrote a bad item name, it
+ // should have failed in astconv.
+ bug!(
+ "No associated type `{}` for {}",
+ tcx.item_name(assoc_def_id),
+ tcx.def_path_str(impl_def_id)
+ )
+ }
+}
--- /dev/null
+// known-bug
+
+// This should compile but fails with the current solver.
+//
+// This checks that the new solver uses `Ambiguous` when hitting the
+// inductive cycle here when proving `exists<^0, ^1> (): Trait<^0, ^1>`
+// which requires proving `Trait<?1, ?0>` but that has the same
+// canonical representation.
+trait Trait<T, U> {}
+
+impl<T, U> Trait<T, U> for ()
+where
+ (): Trait<U, T>,
+ T: OtherTrait,
+{}
+
+trait OtherTrait {}
+impl OtherTrait for u32 {}
+
+fn require_trait<T, U>()
+where
+ (): Trait<T, U>
+{}
+
+fn main() {
+ require_trait::<_, _>();
+ //~^ ERROR overflow evaluating
+}
--- /dev/null
+error[E0275]: overflow evaluating the requirement `_: Sized`
+ --> $DIR/inductive-canonical-cycle.rs:26:5
+ |
+LL | require_trait::<_, _>();
+ | ^^^^^^^^^^^^^^^^^^^^^
+ |
+ = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_canonical_cycle`)
+note: required for `()` to implement `Trait<_, _>`
+ --> $DIR/inductive-canonical-cycle.rs:11:12
+ |
+LL | impl<T, U> Trait<T, U> for ()
+ | ^^^^^^^^^^^ ^^
+ = note: 128 redundant requirements hidden
+ = note: required for `()` to implement `Trait<_, _>`
+note: required by a bound in `require_trait`
+ --> $DIR/inductive-canonical-cycle.rs:22:9
+ |
+LL | fn require_trait<T, U>()
+ | ------------- required by a bound in this
+LL | where
+LL | (): Trait<T, U>
+ | ^^^^^^^^^^^ required by this bound in `require_trait`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.
message = "Some changes occured in `rustc_ty_utils::consts.rs`"
cc = ["@BoxyUwU"]
+[mentions."compiler/rustc_trait_selection/src/solve]
+message = "Some changes occurred to the core trait solver"
+cc = ["@lcnr"]
+
[mentions."compiler/rustc_trait_selection/src/traits/engine.rs"]
message = """
Some changes occurred in engine.rs, potentially modifying the public API \
projects / rust.git / commitdiff