719 lines
31 KiB
Rust
719 lines
31 KiB
Rust
use crate::infer::{InferCtxt, TyOrConstInferVar};
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use rustc_data_structures::obligation_forest::ProcessResult;
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use rustc_data_structures::obligation_forest::{Error, ForestObligation, Outcome};
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use rustc_data_structures::obligation_forest::{ObligationForest, ObligationProcessor};
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use rustc_infer::traits::ProjectionCacheKey;
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use rustc_infer::traits::{SelectionError, TraitEngine, TraitObligation};
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use rustc_middle::mir::interpret::ErrorHandled;
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use rustc_middle::ty::abstract_const::NotConstEvaluatable;
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use rustc_middle::ty::error::{ExpectedFound, TypeError};
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use rustc_middle::ty::subst::SubstsRef;
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use rustc_middle::ty::{self, Binder, Const, TypeVisitable};
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use std::marker::PhantomData;
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use super::const_evaluatable;
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use super::project::{self, ProjectAndUnifyResult};
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use super::select::SelectionContext;
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use super::wf;
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use super::CodeAmbiguity;
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use super::CodeProjectionError;
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use super::CodeSelectionError;
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use super::EvaluationResult;
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use super::PredicateObligation;
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use super::Unimplemented;
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use super::{FulfillmentError, FulfillmentErrorCode};
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use crate::traits::project::PolyProjectionObligation;
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use crate::traits::project::ProjectionCacheKeyExt as _;
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use crate::traits::query::evaluate_obligation::InferCtxtExt;
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impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> {
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/// Note that we include both the `ParamEnv` and the `Predicate`,
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/// as the `ParamEnv` can influence whether fulfillment succeeds
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/// or fails.
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type CacheKey = ty::ParamEnvAnd<'tcx, ty::Predicate<'tcx>>;
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fn as_cache_key(&self) -> Self::CacheKey {
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self.obligation.param_env.and(self.obligation.predicate)
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}
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}
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/// The fulfillment context is used to drive trait resolution. It
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/// consists of a list of obligations that must be (eventually)
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/// satisfied. The job is to track which are satisfied, which yielded
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/// errors, and which are still pending. At any point, users can call
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/// `select_where_possible`, and the fulfillment context will try to do
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/// selection, retaining only those obligations that remain
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/// ambiguous. This may be helpful in pushing type inference
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/// along. Once all type inference constraints have been generated, the
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/// method `select_all_or_error` can be used to report any remaining
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/// ambiguous cases as errors.
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pub struct FulfillmentContext<'tcx> {
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// A list of all obligations that have been registered with this
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// fulfillment context.
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predicates: ObligationForest<PendingPredicateObligation<'tcx>>,
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// Is it OK to register obligations into this infcx inside
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// an infcx snapshot?
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//
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// The "primary fulfillment" in many cases in typeck lives
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// outside of any snapshot, so any use of it inside a snapshot
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// will lead to trouble and therefore is checked against, but
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// other fulfillment contexts sometimes do live inside of
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// a snapshot (they don't *straddle* a snapshot, so there
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// is no trouble there).
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usable_in_snapshot: bool,
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}
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#[derive(Clone, Debug)]
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pub struct PendingPredicateObligation<'tcx> {
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pub obligation: PredicateObligation<'tcx>,
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// This is far more often read than modified, meaning that we
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// should mostly optimize for reading speed, while modifying is not as relevant.
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//
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// For whatever reason using a boxed slice is slower than using a `Vec` here.
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pub stalled_on: Vec<TyOrConstInferVar<'tcx>>,
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}
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// `PendingPredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
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#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
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static_assert_size!(PendingPredicateObligation<'_>, 72);
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impl<'a, 'tcx> FulfillmentContext<'tcx> {
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/// Creates a new fulfillment context.
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pub(super) fn new() -> FulfillmentContext<'tcx> {
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FulfillmentContext { predicates: ObligationForest::new(), usable_in_snapshot: false }
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}
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pub(super) fn new_in_snapshot() -> FulfillmentContext<'tcx> {
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FulfillmentContext { predicates: ObligationForest::new(), usable_in_snapshot: true }
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}
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/// Attempts to select obligations using `selcx`.
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fn select(&mut self, selcx: SelectionContext<'a, 'tcx>) -> Vec<FulfillmentError<'tcx>> {
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let span = debug_span!("select", obligation_forest_size = ?self.predicates.len());
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let _enter = span.enter();
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// Process pending obligations.
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let outcome: Outcome<_, _> =
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self.predicates.process_obligations(&mut FulfillProcessor { selcx });
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// FIXME: if we kept the original cache key, we could mark projection
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// obligations as complete for the projection cache here.
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let errors: Vec<FulfillmentError<'tcx>> =
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outcome.errors.into_iter().map(to_fulfillment_error).collect();
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debug!(
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"select({} predicates remaining, {} errors) done",
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self.predicates.len(),
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errors.len()
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);
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errors
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}
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}
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impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
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fn register_predicate_obligation(
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&mut self,
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infcx: &InferCtxt<'tcx>,
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obligation: PredicateObligation<'tcx>,
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) {
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// this helps to reduce duplicate errors, as well as making
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// debug output much nicer to read and so on.
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let obligation = infcx.resolve_vars_if_possible(obligation);
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debug!(?obligation, "register_predicate_obligation");
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assert!(!infcx.is_in_snapshot() || self.usable_in_snapshot);
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self.predicates
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.register_obligation(PendingPredicateObligation { obligation, stalled_on: vec![] });
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}
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fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
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{
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let errors = self.select_where_possible(infcx);
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if !errors.is_empty() {
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return errors;
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}
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}
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self.predicates.to_errors(CodeAmbiguity).into_iter().map(to_fulfillment_error).collect()
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}
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fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
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let selcx = SelectionContext::new(infcx);
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self.select(selcx)
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}
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fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
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self.predicates.map_pending_obligations(|o| o.obligation.clone())
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}
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}
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struct FulfillProcessor<'a, 'tcx> {
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selcx: SelectionContext<'a, 'tcx>,
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}
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fn mk_pending(os: Vec<PredicateObligation<'_>>) -> Vec<PendingPredicateObligation<'_>> {
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os.into_iter()
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.map(|o| PendingPredicateObligation { obligation: o, stalled_on: vec![] })
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.collect()
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}
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impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
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type Obligation = PendingPredicateObligation<'tcx>;
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type Error = FulfillmentErrorCode<'tcx>;
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type OUT = Outcome<Self::Obligation, Self::Error>;
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/// Identifies whether a predicate obligation needs processing.
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///
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/// This is always inlined, despite its size, because it has a single
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/// callsite and it is called *very* frequently.
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#[inline(always)]
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fn needs_process_obligation(&self, pending_obligation: &Self::Obligation) -> bool {
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// If we were stalled on some unresolved variables, first check whether
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// any of them have been resolved; if not, don't bother doing more work
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// yet.
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match pending_obligation.stalled_on.len() {
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// Match arms are in order of frequency, which matters because this
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// code is so hot. 1 and 0 dominate; 2+ is fairly rare.
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1 => {
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let infer_var = pending_obligation.stalled_on[0];
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self.selcx.infcx.ty_or_const_infer_var_changed(infer_var)
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}
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0 => {
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// In this case we haven't changed, but wish to make a change.
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true
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}
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_ => {
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// This `for` loop was once a call to `all()`, but this lower-level
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// form was a perf win. See #64545 for details.
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(|| {
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for &infer_var in &pending_obligation.stalled_on {
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if self.selcx.infcx.ty_or_const_infer_var_changed(infer_var) {
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return true;
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}
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}
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false
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})()
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}
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}
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}
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/// Processes a predicate obligation and returns either:
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/// - `Changed(v)` if the predicate is true, presuming that `v` are also true
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/// - `Unchanged` if we don't have enough info to be sure
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/// - `Error(e)` if the predicate does not hold
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///
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/// This is called much less often than `needs_process_obligation`, so we
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/// never inline it.
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#[inline(never)]
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#[instrument(level = "debug", skip(self, pending_obligation))]
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fn process_obligation(
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&mut self,
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pending_obligation: &mut PendingPredicateObligation<'tcx>,
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) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> {
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pending_obligation.stalled_on.truncate(0);
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let obligation = &mut pending_obligation.obligation;
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debug!(?obligation, "pre-resolve");
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if obligation.predicate.has_non_region_infer() {
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obligation.predicate = self.selcx.infcx.resolve_vars_if_possible(obligation.predicate);
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}
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let obligation = &pending_obligation.obligation;
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let infcx = self.selcx.infcx;
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if obligation.predicate.has_projections() {
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let mut obligations = Vec::new();
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let predicate = crate::traits::project::try_normalize_with_depth_to(
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&mut self.selcx,
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obligation.param_env,
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obligation.cause.clone(),
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obligation.recursion_depth + 1,
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obligation.predicate,
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&mut obligations,
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);
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if predicate != obligation.predicate {
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obligations.push(obligation.with(infcx.tcx, predicate));
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return ProcessResult::Changed(mk_pending(obligations));
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}
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}
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let binder = obligation.predicate.kind();
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match binder.no_bound_vars() {
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None => match binder.skip_binder() {
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// Evaluation will discard candidates using the leak check.
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// This means we need to pass it the bound version of our
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// predicate.
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ty::PredicateKind::Clause(ty::Clause::Trait(trait_ref)) => {
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let trait_obligation = obligation.with(infcx.tcx, binder.rebind(trait_ref));
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self.process_trait_obligation(
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obligation,
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trait_obligation,
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&mut pending_obligation.stalled_on,
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)
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}
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ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
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let project_obligation = obligation.with(infcx.tcx, binder.rebind(data));
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self.process_projection_obligation(
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obligation,
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project_obligation,
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&mut pending_obligation.stalled_on,
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)
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}
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ty::PredicateKind::Clause(ty::Clause::RegionOutlives(_))
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| ty::PredicateKind::Clause(ty::Clause::TypeOutlives(_))
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| ty::PredicateKind::WellFormed(_)
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| ty::PredicateKind::ObjectSafe(_)
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| ty::PredicateKind::ClosureKind(..)
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| ty::PredicateKind::Subtype(_)
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| ty::PredicateKind::Coerce(_)
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| ty::PredicateKind::ConstEvaluatable(..)
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| ty::PredicateKind::ConstEquate(..) => {
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let pred =
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ty::Binder::dummy(infcx.replace_bound_vars_with_placeholders(binder));
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ProcessResult::Changed(mk_pending(vec![obligation.with(infcx.tcx, pred)]))
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}
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ty::PredicateKind::Ambiguous => ProcessResult::Unchanged,
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ty::PredicateKind::TypeWellFormedFromEnv(..) => {
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bug!("TypeWellFormedFromEnv is only used for Chalk")
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}
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},
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Some(pred) => match pred {
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ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
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let trait_obligation = obligation.with(infcx.tcx, Binder::dummy(data));
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self.process_trait_obligation(
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obligation,
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trait_obligation,
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&mut pending_obligation.stalled_on,
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)
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}
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ty::PredicateKind::Clause(ty::Clause::RegionOutlives(data)) => {
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if infcx.considering_regions {
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infcx.region_outlives_predicate(&obligation.cause, Binder::dummy(data));
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}
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ProcessResult::Changed(vec![])
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}
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ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
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t_a,
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r_b,
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))) => {
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if infcx.considering_regions {
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infcx.register_region_obligation_with_cause(t_a, r_b, &obligation.cause);
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}
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ProcessResult::Changed(vec![])
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}
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ty::PredicateKind::Clause(ty::Clause::Projection(ref data)) => {
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let project_obligation = obligation.with(infcx.tcx, Binder::dummy(*data));
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self.process_projection_obligation(
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obligation,
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project_obligation,
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&mut pending_obligation.stalled_on,
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)
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}
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ty::PredicateKind::ObjectSafe(trait_def_id) => {
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if !self.selcx.tcx().is_object_safe(trait_def_id) {
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ProcessResult::Error(CodeSelectionError(Unimplemented))
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} else {
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ProcessResult::Changed(vec![])
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}
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}
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ty::PredicateKind::ClosureKind(_, closure_substs, kind) => {
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match self.selcx.infcx.closure_kind(closure_substs) {
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Some(closure_kind) => {
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if closure_kind.extends(kind) {
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ProcessResult::Changed(vec![])
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} else {
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ProcessResult::Error(CodeSelectionError(Unimplemented))
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}
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}
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None => ProcessResult::Unchanged,
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}
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}
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ty::PredicateKind::WellFormed(arg) => {
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match wf::obligations(
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self.selcx.infcx,
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obligation.param_env,
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obligation.cause.body_id,
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obligation.recursion_depth + 1,
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arg,
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obligation.cause.span,
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) {
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None => {
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pending_obligation.stalled_on =
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vec![TyOrConstInferVar::maybe_from_generic_arg(arg).unwrap()];
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ProcessResult::Unchanged
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}
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Some(os) => ProcessResult::Changed(mk_pending(os)),
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}
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}
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ty::PredicateKind::Subtype(subtype) => {
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match self.selcx.infcx.subtype_predicate(
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&obligation.cause,
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obligation.param_env,
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Binder::dummy(subtype),
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) {
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Err((a, b)) => {
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// None means that both are unresolved.
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pending_obligation.stalled_on =
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vec![TyOrConstInferVar::Ty(a), TyOrConstInferVar::Ty(b)];
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ProcessResult::Unchanged
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}
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Ok(Ok(ok)) => ProcessResult::Changed(mk_pending(ok.obligations)),
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Ok(Err(err)) => {
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let expected_found =
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ExpectedFound::new(subtype.a_is_expected, subtype.a, subtype.b);
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ProcessResult::Error(FulfillmentErrorCode::CodeSubtypeError(
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expected_found,
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err,
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))
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}
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}
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}
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ty::PredicateKind::Coerce(coerce) => {
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match self.selcx.infcx.coerce_predicate(
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&obligation.cause,
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obligation.param_env,
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Binder::dummy(coerce),
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) {
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Err((a, b)) => {
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// None means that both are unresolved.
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pending_obligation.stalled_on =
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vec![TyOrConstInferVar::Ty(a), TyOrConstInferVar::Ty(b)];
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ProcessResult::Unchanged
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}
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Ok(Ok(ok)) => ProcessResult::Changed(mk_pending(ok.obligations)),
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Ok(Err(err)) => {
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let expected_found = ExpectedFound::new(false, coerce.a, coerce.b);
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ProcessResult::Error(FulfillmentErrorCode::CodeSubtypeError(
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expected_found,
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err,
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))
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}
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}
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}
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|
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ty::PredicateKind::ConstEvaluatable(uv) => {
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match const_evaluatable::is_const_evaluatable(
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self.selcx.infcx,
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uv,
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obligation.param_env,
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obligation.cause.span,
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) {
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Ok(()) => ProcessResult::Changed(vec![]),
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Err(NotConstEvaluatable::MentionsInfer) => {
|
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pending_obligation.stalled_on.clear();
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pending_obligation.stalled_on.extend(
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uv.walk().filter_map(TyOrConstInferVar::maybe_from_generic_arg),
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);
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ProcessResult::Unchanged
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}
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Err(
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e @ NotConstEvaluatable::MentionsParam
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| e @ NotConstEvaluatable::Error(_),
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) => ProcessResult::Error(CodeSelectionError(
|
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SelectionError::NotConstEvaluatable(e),
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)),
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}
|
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}
|
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|
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ty::PredicateKind::ConstEquate(c1, c2) => {
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let tcx = self.selcx.tcx();
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assert!(
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tcx.features().generic_const_exprs,
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"`ConstEquate` without a feature gate: {c1:?} {c2:?}",
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);
|
|
// FIXME: we probably should only try to unify abstract constants
|
|
// if the constants depend on generic parameters.
|
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//
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// Let's just see where this breaks :shrug:
|
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{
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let c1 = tcx.expand_abstract_consts(c1);
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let c2 = tcx.expand_abstract_consts(c2);
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debug!("equating consts:\nc1= {:?}\nc2= {:?}", c1, c2);
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|
|
use rustc_hir::def::DefKind;
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use ty::ConstKind::Unevaluated;
|
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match (c1.kind(), c2.kind()) {
|
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(Unevaluated(a), Unevaluated(b))
|
|
if a.def.did == b.def.did
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&& tcx.def_kind(a.def.did) == DefKind::AssocConst =>
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{
|
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if let Ok(new_obligations) = infcx
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.at(&obligation.cause, obligation.param_env)
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.trace(c1, c2)
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.eq(a.substs, b.substs)
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{
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return ProcessResult::Changed(mk_pending(
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new_obligations.into_obligations(),
|
|
));
|
|
}
|
|
}
|
|
(_, Unevaluated(_)) | (Unevaluated(_), _) => (),
|
|
(_, _) => {
|
|
if let Ok(new_obligations) =
|
|
infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
|
|
{
|
|
return ProcessResult::Changed(mk_pending(
|
|
new_obligations.into_obligations(),
|
|
));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
let stalled_on = &mut pending_obligation.stalled_on;
|
|
|
|
let mut evaluate = |c: Const<'tcx>| {
|
|
if let ty::ConstKind::Unevaluated(unevaluated) = c.kind() {
|
|
match self.selcx.infcx.try_const_eval_resolve(
|
|
obligation.param_env,
|
|
unevaluated,
|
|
c.ty(),
|
|
Some(obligation.cause.span),
|
|
) {
|
|
Ok(val) => Ok(val),
|
|
Err(e) => match e {
|
|
ErrorHandled::TooGeneric => {
|
|
stalled_on.extend(
|
|
unevaluated.substs.iter().filter_map(
|
|
TyOrConstInferVar::maybe_from_generic_arg,
|
|
),
|
|
);
|
|
Err(ErrorHandled::TooGeneric)
|
|
}
|
|
_ => Err(e),
|
|
},
|
|
}
|
|
} else {
|
|
Ok(c)
|
|
}
|
|
};
|
|
|
|
match (evaluate(c1), evaluate(c2)) {
|
|
(Ok(c1), Ok(c2)) => {
|
|
match self
|
|
.selcx
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(c1, c2)
|
|
{
|
|
Ok(inf_ok) => {
|
|
ProcessResult::Changed(mk_pending(inf_ok.into_obligations()))
|
|
}
|
|
Err(err) => ProcessResult::Error(
|
|
FulfillmentErrorCode::CodeConstEquateError(
|
|
ExpectedFound::new(true, c1, c2),
|
|
err,
|
|
),
|
|
),
|
|
}
|
|
}
|
|
(Err(ErrorHandled::Reported(reported)), _)
|
|
| (_, Err(ErrorHandled::Reported(reported))) => ProcessResult::Error(
|
|
CodeSelectionError(SelectionError::NotConstEvaluatable(
|
|
NotConstEvaluatable::Error(reported),
|
|
)),
|
|
),
|
|
(Err(ErrorHandled::TooGeneric), _) | (_, Err(ErrorHandled::TooGeneric)) => {
|
|
if c1.has_non_region_infer() || c2.has_non_region_infer() {
|
|
ProcessResult::Unchanged
|
|
} else {
|
|
// Two different constants using generic parameters ~> error.
|
|
let expected_found = ExpectedFound::new(true, c1, c2);
|
|
ProcessResult::Error(FulfillmentErrorCode::CodeConstEquateError(
|
|
expected_found,
|
|
TypeError::ConstMismatch(expected_found),
|
|
))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
ty::PredicateKind::Ambiguous => ProcessResult::Unchanged,
|
|
ty::PredicateKind::TypeWellFormedFromEnv(..) => {
|
|
bug!("TypeWellFormedFromEnv is only used for Chalk")
|
|
}
|
|
},
|
|
}
|
|
}
|
|
|
|
#[inline(never)]
|
|
fn process_backedge<'c, I>(
|
|
&mut self,
|
|
cycle: I,
|
|
_marker: PhantomData<&'c PendingPredicateObligation<'tcx>>,
|
|
) -> Result<(), FulfillmentErrorCode<'tcx>>
|
|
where
|
|
I: Clone + Iterator<Item = &'c PendingPredicateObligation<'tcx>>,
|
|
{
|
|
if self.selcx.coinductive_match(cycle.clone().map(|s| s.obligation.predicate)) {
|
|
debug!("process_child_obligations: coinductive match");
|
|
Ok(())
|
|
} else {
|
|
let cycle: Vec<_> = cycle.map(|c| c.obligation.clone()).collect();
|
|
Err(FulfillmentErrorCode::CodeCycle(cycle))
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
|
|
#[instrument(level = "debug", skip(self, obligation, stalled_on))]
|
|
fn process_trait_obligation(
|
|
&mut self,
|
|
obligation: &PredicateObligation<'tcx>,
|
|
trait_obligation: TraitObligation<'tcx>,
|
|
stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>,
|
|
) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> {
|
|
let infcx = self.selcx.infcx;
|
|
if obligation.predicate.is_global() {
|
|
// no type variables present, can use evaluation for better caching.
|
|
// FIXME: consider caching errors too.
|
|
if infcx.predicate_must_hold_considering_regions(obligation) {
|
|
debug!(
|
|
"selecting trait at depth {} evaluated to holds",
|
|
obligation.recursion_depth
|
|
);
|
|
return ProcessResult::Changed(vec![]);
|
|
}
|
|
}
|
|
|
|
match self.selcx.select(&trait_obligation) {
|
|
Ok(Some(impl_source)) => {
|
|
debug!("selecting trait at depth {} yielded Ok(Some)", obligation.recursion_depth);
|
|
ProcessResult::Changed(mk_pending(impl_source.nested_obligations()))
|
|
}
|
|
Ok(None) => {
|
|
debug!("selecting trait at depth {} yielded Ok(None)", obligation.recursion_depth);
|
|
|
|
// This is a bit subtle: for the most part, the
|
|
// only reason we can fail to make progress on
|
|
// trait selection is because we don't have enough
|
|
// information about the types in the trait.
|
|
stalled_on.clear();
|
|
stalled_on.extend(substs_infer_vars(
|
|
&self.selcx,
|
|
trait_obligation.predicate.map_bound(|pred| pred.trait_ref.substs),
|
|
));
|
|
|
|
debug!(
|
|
"process_predicate: pending obligation {:?} now stalled on {:?}",
|
|
infcx.resolve_vars_if_possible(obligation.clone()),
|
|
stalled_on
|
|
);
|
|
|
|
ProcessResult::Unchanged
|
|
}
|
|
Err(selection_err) => {
|
|
debug!("selecting trait at depth {} yielded Err", obligation.recursion_depth);
|
|
|
|
ProcessResult::Error(CodeSelectionError(selection_err))
|
|
}
|
|
}
|
|
}
|
|
|
|
fn process_projection_obligation(
|
|
&mut self,
|
|
obligation: &PredicateObligation<'tcx>,
|
|
project_obligation: PolyProjectionObligation<'tcx>,
|
|
stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>,
|
|
) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> {
|
|
let tcx = self.selcx.tcx();
|
|
|
|
if obligation.predicate.is_global() {
|
|
// no type variables present, can use evaluation for better caching.
|
|
// FIXME: consider caching errors too.
|
|
if self.selcx.infcx.predicate_must_hold_considering_regions(obligation) {
|
|
if let Some(key) = ProjectionCacheKey::from_poly_projection_predicate(
|
|
&mut self.selcx,
|
|
project_obligation.predicate,
|
|
) {
|
|
// If `predicate_must_hold_considering_regions` succeeds, then we've
|
|
// evaluated all sub-obligations. We can therefore mark the 'root'
|
|
// obligation as complete, and skip evaluating sub-obligations.
|
|
self.selcx
|
|
.infcx
|
|
.inner
|
|
.borrow_mut()
|
|
.projection_cache()
|
|
.complete(key, EvaluationResult::EvaluatedToOk);
|
|
}
|
|
return ProcessResult::Changed(vec![]);
|
|
} else {
|
|
debug!("Does NOT hold: {:?}", obligation);
|
|
}
|
|
}
|
|
|
|
match project::poly_project_and_unify_type(&mut self.selcx, &project_obligation) {
|
|
ProjectAndUnifyResult::Holds(os) => ProcessResult::Changed(mk_pending(os)),
|
|
ProjectAndUnifyResult::FailedNormalization => {
|
|
stalled_on.clear();
|
|
stalled_on.extend(substs_infer_vars(
|
|
&self.selcx,
|
|
project_obligation.predicate.map_bound(|pred| pred.projection_ty.substs),
|
|
));
|
|
ProcessResult::Unchanged
|
|
}
|
|
// Let the caller handle the recursion
|
|
ProjectAndUnifyResult::Recursive => ProcessResult::Changed(mk_pending(vec![
|
|
project_obligation.with(tcx, project_obligation.predicate),
|
|
])),
|
|
ProjectAndUnifyResult::MismatchedProjectionTypes(e) => {
|
|
ProcessResult::Error(CodeProjectionError(e))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Returns the set of inference variables contained in `substs`.
|
|
fn substs_infer_vars<'a, 'tcx>(
|
|
selcx: &SelectionContext<'a, 'tcx>,
|
|
substs: ty::Binder<'tcx, SubstsRef<'tcx>>,
|
|
) -> impl Iterator<Item = TyOrConstInferVar<'tcx>> {
|
|
selcx
|
|
.infcx
|
|
.resolve_vars_if_possible(substs)
|
|
.skip_binder() // ok because this check doesn't care about regions
|
|
.iter()
|
|
.filter(|arg| arg.has_non_region_infer())
|
|
.flat_map(|arg| {
|
|
let mut walker = arg.walk();
|
|
while let Some(c) = walker.next() {
|
|
if !c.has_non_region_infer() {
|
|
walker.visited.remove(&c);
|
|
walker.skip_current_subtree();
|
|
}
|
|
}
|
|
walker.visited.into_iter()
|
|
})
|
|
.filter_map(TyOrConstInferVar::maybe_from_generic_arg)
|
|
}
|
|
|
|
fn to_fulfillment_error<'tcx>(
|
|
error: Error<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>>,
|
|
) -> FulfillmentError<'tcx> {
|
|
let mut iter = error.backtrace.into_iter();
|
|
let obligation = iter.next().unwrap().obligation;
|
|
// The root obligation is the last item in the backtrace - if there's only
|
|
// one item, then it's the same as the main obligation
|
|
let root_obligation = iter.next_back().map_or_else(|| obligation.clone(), |e| e.obligation);
|
|
FulfillmentError::new(obligation, error.error, root_obligation)
|
|
}
|