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Rollup merge of rust-lang#132119 - compiler-errors:effects-old-solver…
…, r=lcnr Hack out effects support for old solver Opening this for vibes ✨ Turns out that a basic, somewhat incomplete implementation of host effects is achievable in the old trait solver pretty easily. This should be sufficient for us to use in the standard library itself. Regarding incompleteness, maybe we should always treat host predicates as ambiguous in intercrate mode (at least in the old solver) to avoid any worries about accidental impl overlap or something. r? ``@lcnr`` cc ``@fee1-dead``
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,152 @@ | ||
| use rustc_hir as hir; | ||
| use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes, InferCtxt}; | ||
| use rustc_infer::traits::{ImplSource, Obligation, PredicateObligation}; | ||
| use rustc_middle::ty::fast_reject::DeepRejectCtxt; | ||
| use rustc_middle::{span_bug, ty}; | ||
| use rustc_type_ir::solve::NoSolution; | ||
| use thin_vec::ThinVec; | ||
|
|
||
| use super::SelectionContext; | ||
|
|
||
| pub type HostEffectObligation<'tcx> = Obligation<'tcx, ty::HostEffectPredicate<'tcx>>; | ||
|
|
||
| pub enum EvaluationFailure { | ||
| Ambiguous, | ||
| NoSolution, | ||
| } | ||
|
|
||
| pub fn evaluate_host_effect_obligation<'tcx>( | ||
| selcx: &mut SelectionContext<'_, 'tcx>, | ||
| obligation: &HostEffectObligation<'tcx>, | ||
| ) -> Result<ThinVec<PredicateObligation<'tcx>>, EvaluationFailure> { | ||
| if selcx.infcx.intercrate { | ||
| span_bug!( | ||
| obligation.cause.span, | ||
| "should not select host obligation in old solver in intercrate mode" | ||
| ); | ||
| } | ||
|
|
||
| match evaluate_host_effect_from_bounds(selcx, obligation) { | ||
| Ok(result) => return Ok(result), | ||
| Err(EvaluationFailure::Ambiguous) => return Err(EvaluationFailure::Ambiguous), | ||
| Err(EvaluationFailure::NoSolution) => {} | ||
| } | ||
|
|
||
| match evaluate_host_effect_from_selection_candiate(selcx, obligation) { | ||
| Ok(result) => return Ok(result), | ||
| Err(EvaluationFailure::Ambiguous) => return Err(EvaluationFailure::Ambiguous), | ||
| Err(EvaluationFailure::NoSolution) => {} | ||
| } | ||
|
|
||
| Err(EvaluationFailure::NoSolution) | ||
| } | ||
|
|
||
| fn match_candidate<'tcx>( | ||
| infcx: &InferCtxt<'tcx>, | ||
| obligation: &HostEffectObligation<'tcx>, | ||
| candidate: ty::Binder<'tcx, ty::HostEffectPredicate<'tcx>>, | ||
| ) -> Result<ThinVec<PredicateObligation<'tcx>>, NoSolution> { | ||
| if !candidate.skip_binder().host.satisfies(obligation.predicate.host) { | ||
| return Err(NoSolution); | ||
| } | ||
|
|
||
| let candidate = infcx.instantiate_binder_with_fresh_vars( | ||
| obligation.cause.span, | ||
| BoundRegionConversionTime::HigherRankedType, | ||
| candidate, | ||
| ); | ||
|
|
||
| let mut nested = infcx | ||
| .at(&obligation.cause, obligation.param_env) | ||
| .eq(DefineOpaqueTypes::Yes, obligation.predicate.trait_ref, candidate.trait_ref)? | ||
| .into_obligations(); | ||
|
|
||
| for nested in &mut nested { | ||
| nested.set_depth_from_parent(obligation.recursion_depth); | ||
| } | ||
|
|
||
| Ok(nested) | ||
| } | ||
|
|
||
| fn evaluate_host_effect_from_bounds<'tcx>( | ||
| selcx: &mut SelectionContext<'_, 'tcx>, | ||
| obligation: &HostEffectObligation<'tcx>, | ||
| ) -> Result<ThinVec<PredicateObligation<'tcx>>, EvaluationFailure> { | ||
| let infcx = selcx.infcx; | ||
| let drcx = DeepRejectCtxt::relate_rigid_rigid(selcx.tcx()); | ||
| let mut candidate = None; | ||
|
|
||
| for predicate in obligation.param_env.caller_bounds() { | ||
| let bound_predicate = predicate.kind(); | ||
| if let ty::ClauseKind::HostEffect(data) = predicate.kind().skip_binder() { | ||
| let data = bound_predicate.rebind(data); | ||
| if data.skip_binder().trait_ref.def_id != obligation.predicate.trait_ref.def_id { | ||
| continue; | ||
| } | ||
|
|
||
| if !drcx.args_may_unify( | ||
| obligation.predicate.trait_ref.args, | ||
| data.skip_binder().trait_ref.args, | ||
| ) { | ||
| continue; | ||
| } | ||
|
|
||
| let is_match = infcx.probe(|_| match_candidate(infcx, obligation, data).is_ok()); | ||
|
|
||
| if is_match { | ||
| if candidate.is_some() { | ||
| return Err(EvaluationFailure::Ambiguous); | ||
| } else { | ||
| candidate = Some(data); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| if let Some(data) = candidate { | ||
| Ok(match_candidate(infcx, obligation, data) | ||
| .expect("candidate matched before, so it should match again")) | ||
| } else { | ||
| Err(EvaluationFailure::NoSolution) | ||
| } | ||
| } | ||
|
|
||
| fn evaluate_host_effect_from_selection_candiate<'tcx>( | ||
| selcx: &mut SelectionContext<'_, 'tcx>, | ||
| obligation: &HostEffectObligation<'tcx>, | ||
| ) -> Result<ThinVec<PredicateObligation<'tcx>>, EvaluationFailure> { | ||
| let tcx = selcx.tcx(); | ||
| selcx.infcx.commit_if_ok(|_| { | ||
| match selcx.select(&obligation.with(tcx, obligation.predicate.trait_ref)) { | ||
| Ok(None) => Err(EvaluationFailure::Ambiguous), | ||
| Err(_) => Err(EvaluationFailure::NoSolution), | ||
| Ok(Some(source)) => match source { | ||
| ImplSource::UserDefined(impl_) => { | ||
| if tcx.constness(impl_.impl_def_id) != hir::Constness::Const { | ||
| return Err(EvaluationFailure::NoSolution); | ||
| } | ||
|
|
||
| let mut nested = impl_.nested; | ||
| nested.extend( | ||
| tcx.const_conditions(impl_.impl_def_id) | ||
| .instantiate(tcx, impl_.args) | ||
| .into_iter() | ||
| .map(|(trait_ref, _)| { | ||
| obligation.with( | ||
| tcx, | ||
| trait_ref.to_host_effect_clause(tcx, obligation.predicate.host), | ||
| ) | ||
| }), | ||
| ); | ||
|
|
||
| for nested in &mut nested { | ||
| nested.set_depth_from_parent(obligation.recursion_depth); | ||
| } | ||
|
|
||
| Ok(nested) | ||
| } | ||
| _ => Err(EvaluationFailure::NoSolution), | ||
| }, | ||
| } | ||
| }) | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,14 +1,15 @@ | ||
| error: using `#![feature(effects)]` without enabling next trait solver globally | ||
| | | ||
| = note: the next trait solver must be enabled globally for the effects feature to work correctly | ||
| = help: use `-Znext-solver` to enable | ||
|
|
||
| error[E0080]: evaluation of `foo::<()>::{constant#0}` failed | ||
| error[E0277]: the trait bound `T: const Tr` is not satisfied | ||
| --> $DIR/constifconst-call-in-const-position.rs:17:38 | ||
| | | ||
| LL | const fn foo<T: ~const Tr>() -> [u8; T::a()] { | ||
| | ^^^^^^ calling non-const function `<() as Tr>::a` | ||
| | ^^^^^^ | ||
|
|
||
| error[E0277]: the trait bound `T: const Tr` is not satisfied | ||
| --> $DIR/constifconst-call-in-const-position.rs:18:9 | ||
| | | ||
| LL | [0; T::a()] | ||
| | ^^^^^^ | ||
|
|
||
| error: aborting due to 2 previous errors | ||
|
|
||
| For more information about this error, try `rustc --explain E0080`. | ||
| For more information about this error, try `rustc --explain E0277`. |
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