diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs index bd52957d162f2..63a73f8d50d93 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs @@ -3,7 +3,8 @@ use rustc_infer::infer::at::ToTrace; use rustc_infer::infer::canonical::CanonicalVarValues; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use rustc_infer::infer::{ - DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, TyCtxtInferExt, + DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, RegionVariableOrigin, + TyCtxtInferExt, }; use rustc_infer::traits::query::NoSolution; use rustc_infer::traits::ObligationCause; @@ -223,18 +224,20 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> { { debug!("rerunning goal to check result is stable"); let (_orig_values, canonical_goal) = self.canonicalize_goal(goal); - let canonical_response = + let new_canonical_response = EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?; - if !canonical_response.value.var_values.is_identity() { + if !new_canonical_response.value.var_values.is_identity() { bug!( "unstable result: re-canonicalized goal={canonical_goal:#?} \ - response={canonical_response:#?}" + first_response={canonical_response:#?} \ + second_response={new_canonical_response:#?}" ); } - if certainty != canonical_response.value.certainty { + if certainty != new_canonical_response.value.certainty { bug!( "unstable certainty: {certainty:#?} re-canonicalized goal={canonical_goal:#?} \ - response={canonical_response:#?}" + first_response={canonical_response:#?} \ + second_response={new_canonical_response:#?}" ); } } @@ -434,6 +437,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { }) } + pub(super) fn next_region_infer(&self) -> ty::Region<'tcx> { + self.infcx.next_region_var(RegionVariableOrigin::MiscVariable(DUMMY_SP)) + } + pub(super) fn next_const_infer(&self, ty: Ty<'tcx>) -> ty::Const<'tcx> { self.infcx.next_const_var( ty, diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs index 226d29687e3a8..67ad7fb4bd21d 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs @@ -16,7 +16,7 @@ use rustc_infer::infer::canonical::query_response::make_query_region_constraints use rustc_infer::infer::canonical::CanonicalVarValues; use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints}; use rustc_middle::traits::query::NoSolution; -use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData}; +use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData, MaybeCause}; use rustc_middle::ty::{self, BoundVar, GenericArgKind}; use rustc_span::DUMMY_SP; use std::iter; @@ -60,9 +60,27 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { let certainty = certainty.unify_with(goals_certainty); - let external_constraints = self.compute_external_query_constraints()?; + let response = match certainty { + Certainty::Yes | Certainty::Maybe(MaybeCause::Ambiguity) => { + let external_constraints = self.compute_external_query_constraints()?; + Response { var_values: self.var_values, external_constraints, certainty } + } + Certainty::Maybe(MaybeCause::Overflow) => { + // If we have overflow, it's probable that we're substituting a type + // into itself infinitely and any partial substitutions in the query + // response are probably not useful anyways, so just return an empty + // query response. + // + // This may prevent us from potentially useful inference, e.g. + // 2 candidates, one ambiguous and one overflow, which both + // have the same inference constraints. + // + // Changing this to retain some constraints in the future + // won't be a breaking change, so this is good enough for now. + return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow)); + } + }; - let response = Response { var_values: self.var_values, external_constraints, certainty }; let canonical = Canonicalizer::canonicalize( self.infcx, CanonicalizeMode::Response { max_input_universe: self.max_input_universe }, @@ -72,6 +90,40 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { Ok(canonical) } + /// Constructs a totally unconstrained, ambiguous response to a goal. + /// + /// Take care when using this, since often it's useful to respond with + /// ambiguity but return constrained variables to guide inference. + pub(in crate::solve) fn make_ambiguous_response_no_constraints( + &self, + maybe_cause: MaybeCause, + ) -> CanonicalResponse<'tcx> { + let unconstrained_response = Response { + var_values: CanonicalVarValues { + var_values: self.tcx().mk_substs_from_iter(self.var_values.var_values.iter().map( + |arg| -> ty::GenericArg<'tcx> { + match arg.unpack() { + GenericArgKind::Lifetime(_) => self.next_region_infer().into(), + GenericArgKind::Type(_) => self.next_ty_infer().into(), + GenericArgKind::Const(ct) => self.next_const_infer(ct.ty()).into(), + } + }, + )), + }, + external_constraints: self + .tcx() + .mk_external_constraints(ExternalConstraintsData::default()), + certainty: Certainty::Maybe(maybe_cause), + }; + + Canonicalizer::canonicalize( + self.infcx, + CanonicalizeMode::Response { max_input_universe: self.max_input_universe }, + &mut Default::default(), + unconstrained_response, + ) + } + #[instrument(level = "debug", skip(self), ret)] fn compute_external_query_constraints(&self) -> Result, NoSolution> { // Cannot use `take_registered_region_obligations` as we may compute the response diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs index 19bcbd461447d..d94679fef2833 100644 --- a/compiler/rustc_trait_selection/src/solve/mod.rs +++ b/compiler/rustc_trait_selection/src/solve/mod.rs @@ -340,17 +340,17 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { if responses.is_empty() { return Err(NoSolution); } - let certainty = responses.iter().fold(Certainty::AMBIGUOUS, |certainty, response| { - certainty.unify_with(response.value.certainty) - }); - - let response = self.evaluate_added_goals_and_make_canonical_response(certainty); - if let Ok(response) = response { - assert!(response.has_no_inference_or_external_constraints()); - Ok(response) - } else { - bug!("failed to make floundered response: {responses:?}"); - } + + let Certainty::Maybe(maybe_cause) = responses.iter().fold( + Certainty::AMBIGUOUS, + |certainty, response| { + certainty.unify_with(response.value.certainty) + }, + ) else { + bug!("expected flounder response to be ambiguous") + }; + + Ok(self.make_ambiguous_response_no_constraints(maybe_cause)) } } diff --git a/tests/ui/traits/new-solver/exponential-trait-goals.rs b/tests/ui/traits/new-solver/exponential-trait-goals.rs new file mode 100644 index 0000000000000..b37f09ee185e9 --- /dev/null +++ b/tests/ui/traits/new-solver/exponential-trait-goals.rs @@ -0,0 +1,20 @@ +// compile-flags: -Ztrait-solver=next + +trait Trait {} + +struct W(T); + +impl Trait for W<(W, W)> +where + W: Trait, + W: Trait, +{ +} + +fn impls() {} + +fn main() { + impls::>(); + //~^ ERROR type annotations needed + //~| ERROR overflow evaluating the requirement `W<_>: Trait` +} diff --git a/tests/ui/traits/new-solver/exponential-trait-goals.stderr b/tests/ui/traits/new-solver/exponential-trait-goals.stderr new file mode 100644 index 0000000000000..28a99cbbca6a1 --- /dev/null +++ b/tests/ui/traits/new-solver/exponential-trait-goals.stderr @@ -0,0 +1,23 @@ +error[E0282]: type annotations needed + --> $DIR/exponential-trait-goals.rs:17:5 + | +LL | impls::>(); + | ^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `impls` + +error[E0275]: overflow evaluating the requirement `W<_>: Trait` + --> $DIR/exponential-trait-goals.rs:17:5 + | +LL | impls::>(); + | ^^^^^^^^^^^^^ + | + = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`exponential_trait_goals`) +note: required by a bound in `impls` + --> $DIR/exponential-trait-goals.rs:14:13 + | +LL | fn impls() {} + | ^^^^^ required by this bound in `impls` + +error: aborting due to 2 previous errors + +Some errors have detailed explanations: E0275, E0282. +For more information about an error, try `rustc --explain E0275`.