Rollup merge of #77305 - lcnr:candidate_from_obligation, r=davidtwco
move candidate_from_obligation_no_cache It's only called from `candidate_from_obligation` which is already in this file.
This commit is contained in:
commit
6d3cfd9d51
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@ -7,14 +7,19 @@
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//! [rustc dev guide]:https://rustc-dev-guide.rust-lang.org/traits/resolution.html#candidate-assembly
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use rustc_hir as hir;
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use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
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use rustc_middle::ty::print::with_no_trimmed_paths;
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use rustc_middle::ty::{self, TypeFoldable};
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use rustc_target::spec::abi::Abi;
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use crate::traits::coherence::Conflict;
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use crate::traits::{util, SelectionResult};
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use crate::traits::{Overflow, Unimplemented};
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use super::BuiltinImplConditions;
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use super::IntercrateAmbiguityCause;
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use super::OverflowError;
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use super::SelectionCandidate::{self, *};
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use super::{SelectionCandidateSet, SelectionContext, TraitObligationStack};
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use super::{EvaluatedCandidate, SelectionCandidateSet, SelectionContext, TraitObligationStack};
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impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
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pub(super) fn candidate_from_obligation<'o>(
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@ -62,6 +67,161 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
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candidate
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}
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fn candidate_from_obligation_no_cache<'o>(
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&mut self,
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stack: &TraitObligationStack<'o, 'tcx>,
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) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
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if let Some(conflict) = self.is_knowable(stack) {
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debug!("coherence stage: not knowable");
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if self.intercrate_ambiguity_causes.is_some() {
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debug!("evaluate_stack: intercrate_ambiguity_causes is some");
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// Heuristics: show the diagnostics when there are no candidates in crate.
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if let Ok(candidate_set) = self.assemble_candidates(stack) {
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let mut no_candidates_apply = true;
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for c in candidate_set.vec.iter() {
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if self.evaluate_candidate(stack, &c)?.may_apply() {
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no_candidates_apply = false;
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break;
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}
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}
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if !candidate_set.ambiguous && no_candidates_apply {
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let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
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let self_ty = trait_ref.self_ty();
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let (trait_desc, self_desc) = with_no_trimmed_paths(|| {
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let trait_desc = trait_ref.print_only_trait_path().to_string();
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let self_desc = if self_ty.has_concrete_skeleton() {
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Some(self_ty.to_string())
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} else {
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None
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};
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(trait_desc, self_desc)
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});
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let cause = if let Conflict::Upstream = conflict {
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IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_desc, self_desc }
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} else {
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IntercrateAmbiguityCause::DownstreamCrate { trait_desc, self_desc }
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};
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debug!("evaluate_stack: pushing cause = {:?}", cause);
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self.intercrate_ambiguity_causes.as_mut().unwrap().push(cause);
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}
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}
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}
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return Ok(None);
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}
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let candidate_set = self.assemble_candidates(stack)?;
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if candidate_set.ambiguous {
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debug!("candidate set contains ambig");
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return Ok(None);
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}
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let mut candidates = candidate_set.vec;
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debug!("assembled {} candidates for {:?}: {:?}", candidates.len(), stack, candidates);
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// At this point, we know that each of the entries in the
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// candidate set is *individually* applicable. Now we have to
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// figure out if they contain mutual incompatibilities. This
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// frequently arises if we have an unconstrained input type --
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// for example, we are looking for `$0: Eq` where `$0` is some
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// unconstrained type variable. In that case, we'll get a
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// candidate which assumes $0 == int, one that assumes `$0 ==
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// usize`, etc. This spells an ambiguity.
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// If there is more than one candidate, first winnow them down
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// by considering extra conditions (nested obligations and so
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// forth). We don't winnow if there is exactly one
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// candidate. This is a relatively minor distinction but it
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// can lead to better inference and error-reporting. An
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// example would be if there was an impl:
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//
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// impl<T:Clone> Vec<T> { fn push_clone(...) { ... } }
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//
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// and we were to see some code `foo.push_clone()` where `boo`
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// is a `Vec<Bar>` and `Bar` does not implement `Clone`. If
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// we were to winnow, we'd wind up with zero candidates.
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// Instead, we select the right impl now but report "`Bar` does
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// not implement `Clone`".
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if candidates.len() == 1 {
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return self.filter_negative_and_reservation_impls(candidates.pop().unwrap());
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}
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// Winnow, but record the exact outcome of evaluation, which
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// is needed for specialization. Propagate overflow if it occurs.
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let mut candidates = candidates
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.into_iter()
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.map(|c| match self.evaluate_candidate(stack, &c) {
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Ok(eval) if eval.may_apply() => {
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Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
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}
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Ok(_) => Ok(None),
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Err(OverflowError) => Err(Overflow),
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})
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.flat_map(Result::transpose)
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.collect::<Result<Vec<_>, _>>()?;
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debug!("winnowed to {} candidates for {:?}: {:?}", candidates.len(), stack, candidates);
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let needs_infer = stack.obligation.predicate.needs_infer();
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// If there are STILL multiple candidates, we can further
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// reduce the list by dropping duplicates -- including
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// resolving specializations.
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if candidates.len() > 1 {
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let mut i = 0;
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while i < candidates.len() {
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let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| {
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self.candidate_should_be_dropped_in_favor_of(
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&candidates[i],
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&candidates[j],
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needs_infer,
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)
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});
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if is_dup {
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debug!("Dropping candidate #{}/{}: {:?}", i, candidates.len(), candidates[i]);
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candidates.swap_remove(i);
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} else {
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debug!("Retaining candidate #{}/{}: {:?}", i, candidates.len(), candidates[i]);
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i += 1;
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// If there are *STILL* multiple candidates, give up
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// and report ambiguity.
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if i > 1 {
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debug!("multiple matches, ambig");
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return Ok(None);
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}
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}
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}
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}
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// If there are *NO* candidates, then there are no impls --
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// that we know of, anyway. Note that in the case where there
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// are unbound type variables within the obligation, it might
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// be the case that you could still satisfy the obligation
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// from another crate by instantiating the type variables with
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// a type from another crate that does have an impl. This case
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// is checked for in `evaluate_stack` (and hence users
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// who might care about this case, like coherence, should use
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// that function).
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if candidates.is_empty() {
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// If there's an error type, 'downgrade' our result from
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// `Err(Unimplemented)` to `Ok(None)`. This helps us avoid
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// emitting additional spurious errors, since we're guaranteed
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// to have emitted at least one.
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if stack.obligation.references_error() {
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debug!("no results for error type, treating as ambiguous");
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return Ok(None);
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}
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return Err(Unimplemented);
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}
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// Just one candidate left.
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self.filter_negative_and_reservation_impls(candidates.pop().unwrap().candidate)
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}
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pub(super) fn assemble_candidates<'o>(
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&mut self,
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stack: &TraitObligationStack<'o, 'tcx>,
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@ -1029,161 +1029,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
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Ok(Some(candidate))
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}
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fn candidate_from_obligation_no_cache<'o>(
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&mut self,
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stack: &TraitObligationStack<'o, 'tcx>,
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) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
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if let Some(conflict) = self.is_knowable(stack) {
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debug!("coherence stage: not knowable");
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if self.intercrate_ambiguity_causes.is_some() {
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debug!("evaluate_stack: intercrate_ambiguity_causes is some");
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// Heuristics: show the diagnostics when there are no candidates in crate.
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if let Ok(candidate_set) = self.assemble_candidates(stack) {
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let mut no_candidates_apply = true;
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for c in candidate_set.vec.iter() {
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if self.evaluate_candidate(stack, &c)?.may_apply() {
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no_candidates_apply = false;
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break;
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}
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}
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if !candidate_set.ambiguous && no_candidates_apply {
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let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
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let self_ty = trait_ref.self_ty();
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let (trait_desc, self_desc) = with_no_trimmed_paths(|| {
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let trait_desc = trait_ref.print_only_trait_path().to_string();
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let self_desc = if self_ty.has_concrete_skeleton() {
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Some(self_ty.to_string())
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} else {
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None
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};
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(trait_desc, self_desc)
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});
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let cause = if let Conflict::Upstream = conflict {
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IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_desc, self_desc }
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} else {
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IntercrateAmbiguityCause::DownstreamCrate { trait_desc, self_desc }
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};
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debug!("evaluate_stack: pushing cause = {:?}", cause);
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self.intercrate_ambiguity_causes.as_mut().unwrap().push(cause);
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}
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}
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}
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return Ok(None);
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}
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let candidate_set = self.assemble_candidates(stack)?;
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if candidate_set.ambiguous {
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debug!("candidate set contains ambig");
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return Ok(None);
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}
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let mut candidates = candidate_set.vec;
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debug!("assembled {} candidates for {:?}: {:?}", candidates.len(), stack, candidates);
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// At this point, we know that each of the entries in the
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// candidate set is *individually* applicable. Now we have to
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// figure out if they contain mutual incompatibilities. This
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// frequently arises if we have an unconstrained input type --
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// for example, we are looking for `$0: Eq` where `$0` is some
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// unconstrained type variable. In that case, we'll get a
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// candidate which assumes $0 == int, one that assumes `$0 ==
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// usize`, etc. This spells an ambiguity.
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// If there is more than one candidate, first winnow them down
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// by considering extra conditions (nested obligations and so
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// forth). We don't winnow if there is exactly one
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// candidate. This is a relatively minor distinction but it
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// can lead to better inference and error-reporting. An
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// example would be if there was an impl:
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//
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// impl<T:Clone> Vec<T> { fn push_clone(...) { ... } }
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//
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// and we were to see some code `foo.push_clone()` where `boo`
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// is a `Vec<Bar>` and `Bar` does not implement `Clone`. If
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// we were to winnow, we'd wind up with zero candidates.
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// Instead, we select the right impl now but report "`Bar` does
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// not implement `Clone`".
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if candidates.len() == 1 {
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return self.filter_negative_and_reservation_impls(candidates.pop().unwrap());
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}
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// Winnow, but record the exact outcome of evaluation, which
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// is needed for specialization. Propagate overflow if it occurs.
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let mut candidates = candidates
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.into_iter()
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.map(|c| match self.evaluate_candidate(stack, &c) {
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Ok(eval) if eval.may_apply() => {
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Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
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}
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Ok(_) => Ok(None),
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Err(OverflowError) => Err(Overflow),
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})
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.flat_map(Result::transpose)
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.collect::<Result<Vec<_>, _>>()?;
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debug!("winnowed to {} candidates for {:?}: {:?}", candidates.len(), stack, candidates);
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let needs_infer = stack.obligation.predicate.needs_infer();
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// If there are STILL multiple candidates, we can further
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// reduce the list by dropping duplicates -- including
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// resolving specializations.
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if candidates.len() > 1 {
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let mut i = 0;
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while i < candidates.len() {
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let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| {
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self.candidate_should_be_dropped_in_favor_of(
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&candidates[i],
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&candidates[j],
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needs_infer,
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)
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});
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if is_dup {
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debug!("Dropping candidate #{}/{}: {:?}", i, candidates.len(), candidates[i]);
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candidates.swap_remove(i);
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} else {
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debug!("Retaining candidate #{}/{}: {:?}", i, candidates.len(), candidates[i]);
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i += 1;
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// If there are *STILL* multiple candidates, give up
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// and report ambiguity.
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if i > 1 {
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debug!("multiple matches, ambig");
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return Ok(None);
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}
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}
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}
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}
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// If there are *NO* candidates, then there are no impls --
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// that we know of, anyway. Note that in the case where there
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// are unbound type variables within the obligation, it might
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// be the case that you could still satisfy the obligation
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// from another crate by instantiating the type variables with
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// a type from another crate that does have an impl. This case
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// is checked for in `evaluate_stack` (and hence users
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// who might care about this case, like coherence, should use
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// that function).
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if candidates.is_empty() {
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// If there's an error type, 'downgrade' our result from
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// `Err(Unimplemented)` to `Ok(None)`. This helps us avoid
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// emitting additional spurious errors, since we're guaranteed
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// to have emitted at least one.
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if stack.obligation.references_error() {
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debug!("no results for error type, treating as ambiguous");
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return Ok(None);
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}
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return Err(Unimplemented);
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}
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// Just one candidate left.
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self.filter_negative_and_reservation_impls(candidates.pop().unwrap().candidate)
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}
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fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Option<Conflict> {
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debug!("is_knowable(intercrate={:?})", self.intercrate);
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