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Rollup merge of #133643 - lcnr:merge-candidates, r=compiler-errors

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-Znext-solver: modify candidate preference rules

This implements the design proposed in the FCP in #132325 and matches the old solver behavior. I hope the inline comments are all sufficiently clear, I personally think this is a fairly clear improvement over the existing approach using `fn discard_impls_shadowed_by_env`. This fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/96.

This also fixes #133639 which encounters an ICE in negative coherence when evaluating the where-clause. Given the features required to trigger this ICE 🤷

r? ``@compiler-errors``
This commit is contained in:
Jacob Pratt 2024-12-18 21:38:08 -05:00 • committed by GitHub
commit 4cd157e6b9
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GPG key ID: B5690EEEBB952194
22 changed files with 334 additions and 183 deletions
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2
compiler/rustc_middle/src/ty/mod.rs
View file

@ -971,7 +971,7 @@ pub struct ParamEnv<'tcx> {
}
impl<'tcx> rustc_type_ir::inherent::ParamEnv<TyCtxt<'tcx>> for ParamEnv<'tcx> {
fn caller_bounds(self) -> impl IntoIterator<Item = ty::Clause<'tcx>> {
fn caller_bounds(self) -> impl inherent::SliceLike<Item = ty::Clause<'tcx>> {
self.caller_bounds()
}
}

119
compiler/rustc_next_trait_solver/src/canonicalizer.rs
View file

@ -3,6 +3,7 @@ use std::cmp::Ordering;
use rustc_type_ir::data_structures::HashMap;
use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
use rustc_type_ir::inherent::*;
use rustc_type_ir::solve::{Goal, QueryInput};
use rustc_type_ir::visit::TypeVisitableExt;
use rustc_type_ir::{
self as ty, Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, InferCtxtLike,
@ -17,8 +18,11 @@ use crate::delegate::SolverDelegate;
/// while canonicalizing the response happens in the context of the
/// query.
#[derive(Debug, Clone, Copy)]
pub enum CanonicalizeMode {
Input,
enum CanonicalizeMode {
/// When canonicalizing the `param_env`, we keep `'static` as merging
/// trait candidates relies on it when deciding whether a where-bound
/// is trivial.
Input { keep_static: bool },
/// FIXME: We currently return region constraints referring to
/// placeholders and inference variables from a binder instantiated
/// inside of the query.
@ -59,15 +63,15 @@ pub struct Canonicalizer<'a, D: SolverDelegate<Interner = I>, I: Interner> {
}
impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
pub fn canonicalize<T: TypeFoldable<I>>(
pub fn canonicalize_response<T: TypeFoldable<I>>(
delegate: &'a D,
canonicalize_mode: CanonicalizeMode,
max_input_universe: ty::UniverseIndex,
variables: &'a mut Vec<I::GenericArg>,
value: T,
) -> ty::Canonical<I, T> {
let mut canonicalizer = Canonicalizer {
delegate,
canonicalize_mode,
canonicalize_mode: CanonicalizeMode::Response { max_input_universe },
variables,
variable_lookup_table: Default::default(),
@ -80,9 +84,67 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
let value = value.fold_with(&mut canonicalizer);
assert!(!value.has_infer(), "unexpected infer in {value:?}");
assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
let (max_universe, variables) = canonicalizer.finalize();
Canonical { max_universe, variables, value }
}
/// When canonicalizing query inputs, we keep `'static` in the `param_env`
/// but erase it everywhere else. We generally don't want to depend on region
/// identity, so while it should not matter whether `'static` is kept in the
/// value or opaque type storage as well, this prevents us from accidentally
/// relying on it in the future.
///
/// We want to keep the option of canonicalizing `'static` to an existential
/// variable in the future by changing the way we detect global where-bounds.
pub fn canonicalize_input<P: TypeFoldable<I>>(
delegate: &'a D,
variables: &'a mut Vec<I::GenericArg>,
input: QueryInput<I, P>,
) -> ty::Canonical<I, QueryInput<I, P>> {
// First canonicalize the `param_env` while keeping `'static`
let mut env_canonicalizer = Canonicalizer {
delegate,
canonicalize_mode: CanonicalizeMode::Input { keep_static: true },
variables,
variable_lookup_table: Default::default(),
primitive_var_infos: Vec::new(),
binder_index: ty::INNERMOST,
cache: Default::default(),
};
let param_env = input.goal.param_env.fold_with(&mut env_canonicalizer);
debug_assert_eq!(env_canonicalizer.binder_index, ty::INNERMOST);
// Then canonicalize the rest of the input without keeping `'static`
// while *mostly* reusing the canonicalizer from above.
let mut rest_canonicalizer = Canonicalizer {
delegate,
canonicalize_mode: CanonicalizeMode::Input { keep_static: false },
variables: env_canonicalizer.variables,
// We're able to reuse the `variable_lookup_table` as whether or not
// it already contains an entry for `'static` does not matter.
variable_lookup_table: env_canonicalizer.variable_lookup_table,
primitive_var_infos: env_canonicalizer.primitive_var_infos,
binder_index: ty::INNERMOST,
// We do not reuse the cache as it may contain entries whose canonicalized
// value contains `'static`. While we could alternatively handle this by
// checking for `'static` when using cached entries, this does not
// feel worth the effort. I do not expect that a `ParamEnv` will ever
// contain large enough types for caching to be necessary.
cache: Default::default(),
};
let predicate = input.goal.predicate.fold_with(&mut rest_canonicalizer);
let goal = Goal { param_env, predicate };
let predefined_opaques_in_body =
input.predefined_opaques_in_body.fold_with(&mut rest_canonicalizer);
let value = QueryInput { goal, predefined_opaques_in_body };
assert!(!value.has_infer(), "unexpected infer in {value:?}");
assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
let (max_universe, variables) = rest_canonicalizer.finalize();
Canonical { max_universe, variables, value }
}
@ -126,7 +188,7 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
// all information which should not matter for the solver.
//
// For this we compress universes as much as possible.
CanonicalizeMode::Input => {}
CanonicalizeMode::Input { .. } => {}
// When canonicalizing a response we map a universes already entered
// by the caller to the root universe and only return useful universe
// information for placeholders and inference variables created inside
@ -290,17 +352,15 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
}
},
ty::Placeholder(placeholder) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(PlaceholderLike::new(
placeholder.universe(),
self.variables.len().into(),
)),
CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderTy(
PlaceholderLike::new(placeholder.universe(), self.variables.len().into()),
),
CanonicalizeMode::Response { .. } => CanonicalVarKind::PlaceholderTy(placeholder),
},
ty::Param(_) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(PlaceholderLike::new(
ty::UniverseIndex::ROOT,
self.variables.len().into(),
)),
CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderTy(
PlaceholderLike::new(ty::UniverseIndex::ROOT, self.variables.len().into()),
),
CanonicalizeMode::Response { .. } => panic!("param ty in response: {t:?}"),
},
ty::Bool
@ -357,21 +417,30 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
let kind = match r.kind() {
ty::ReBound(..) => return r,
// We may encounter `ReStatic` in item signatures or the hidden type
// of an opaque. `ReErased` should only be encountered in the hidden
// We don't canonicalize `ReStatic` in the `param_env` as we use it
// when checking whether a `ParamEnv` candidate is global.
ty::ReStatic => match self.canonicalize_mode {
CanonicalizeMode::Input { keep_static: false } => {
CanonicalVarKind::Region(ty::UniverseIndex::ROOT)
}
CanonicalizeMode::Input { keep_static: true }
| CanonicalizeMode::Response { .. } => return r,
},
// `ReErased` should only be encountered in the hidden
// type of an opaque for regions that are ignored for the purposes of
// captures.
//
// FIXME: We should investigate the perf implications of not uniquifying
// `ReErased`. We may be able to short-circuit registering region
// obligations if we encounter a `ReErased` on one side, for example.
ty::ReStatic | ty::ReErased | ty::ReError(_) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
ty::ReErased | ty::ReError(_) => match self.canonicalize_mode {
CanonicalizeMode::Input { .. } => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Response { .. } => return r,
},
ty::ReEarlyParam(_) | ty::ReLateParam(_) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Input { .. } => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Response { .. } => {
panic!("unexpected region in response: {r:?}")
}
@ -379,7 +448,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
ty::RePlaceholder(placeholder) => match self.canonicalize_mode {
// We canonicalize placeholder regions as existentials in query inputs.
CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Input { .. } => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Response { max_input_universe } => {
// If we have a placeholder region inside of a query, it must be from
// a new universe.
@ -397,7 +466,9 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
"region vid should have been resolved fully before canonicalization"
);
match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Input { keep_static: _ } => {
CanonicalVarKind::Region(ty::UniverseIndex::ROOT)
}
CanonicalizeMode::Response { .. } => {
CanonicalVarKind::Region(self.delegate.universe_of_lt(vid).unwrap())
}
@ -434,7 +505,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
ty::InferConst::Fresh(_) => todo!(),
},
ty::ConstKind::Placeholder(placeholder) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::PlaceholderConst(
CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderConst(
PlaceholderLike::new(placeholder.universe(), self.variables.len().into()),
),
CanonicalizeMode::Response { .. } => {
@ -442,7 +513,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
}
},
ty::ConstKind::Param(_) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::PlaceholderConst(
CanonicalizeMode::Input { .. } => CanonicalVarKind::PlaceholderConst(
PlaceholderLike::new(ty::UniverseIndex::ROOT, self.variables.len().into()),
),
CanonicalizeMode::Response { .. } => panic!("param ty in response: {c:?}"),

134
compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
View file

@ -11,6 +11,7 @@ use rustc_type_ir::visit::TypeVisitableExt as _;
use rustc_type_ir::{self as ty, Interner, TypingMode, Upcast as _, elaborate};
use tracing::{debug, instrument};
use super::trait_goals::TraitGoalProvenVia;
use crate::delegate::SolverDelegate;
use crate::solve::inspect::ProbeKind;
use crate::solve::{
@ -337,15 +338,6 @@ where
self.assemble_param_env_candidates(goal, &mut candidates);
match self.typing_mode() {
TypingMode::Coherence => {}
TypingMode::Analysis { .. }
| TypingMode::PostBorrowckAnalysis { .. }
| TypingMode::PostAnalysis => {
self.discard_impls_shadowed_by_env(goal, &mut candidates);
}
}
candidates
}
@ -500,7 +492,7 @@ where
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
for (i, assumption) in goal.param_env.caller_bounds().into_iter().enumerate() {
for (i, assumption) in goal.param_env.caller_bounds().iter().enumerate() {
candidates.extend(G::probe_and_consider_implied_clause(
self,
CandidateSource::ParamEnv(i),
@ -733,72 +725,64 @@ where
})
}
/// If there's a where-bound for the current goal, do not use any impl candidates
/// to prove the current goal. Most importantly, if there is a where-bound which does
/// not specify any associated types, we do not allow normalizing the associated type
/// by using an impl, even if it would apply.
/// We sadly can't simply take all possible candidates for normalization goals
/// and check whether they result in the same constraints. We want to make sure
/// that trying to normalize an alias doesn't result in constraints which aren't
/// otherwise required.
///
/// <https://github.com/rust-lang/trait-system-refactor-initiative/issues/76>
// FIXME(@lcnr): The current structure here makes me unhappy and feels ugly. idk how
// to improve this however. However, this should make it fairly straightforward to refine
// the filtering going forward, so it seems alright-ish for now.
#[instrument(level = "debug", skip(self, goal))]
fn discard_impls_shadowed_by_env<G: GoalKind<D>>(
&mut self,
goal: Goal<I, G>,
candidates: &mut Vec<Candidate<I>>,
) {
let cx = self.cx();
let trait_goal: Goal<I, ty::TraitPredicate<I>> =
goal.with(cx, goal.predicate.trait_ref(cx));
let mut trait_candidates_from_env = vec![];
self.probe(|_| ProbeKind::ShadowedEnvProbing).enter(|ecx| {
ecx.assemble_param_env_candidates(trait_goal, &mut trait_candidates_from_env);
ecx.assemble_alias_bound_candidates(trait_goal, &mut trait_candidates_from_env);
});
if !trait_candidates_from_env.is_empty() {
let trait_env_result = self.merge_candidates(trait_candidates_from_env);
match trait_env_result.unwrap().value.certainty {
// If proving the trait goal succeeds by using the env,
// we freely drop all impl candidates.
//
// FIXME(@lcnr): It feels like this could easily hide
// a forced ambiguity candidate added earlier.
// This feels dangerous.
Certainty::Yes => {
candidates.retain(|c| match c.source {
CandidateSource::Impl(_) | CandidateSource::BuiltinImpl(_) => {
debug!(?c, "discard impl candidate");
false
}
CandidateSource::ParamEnv(_) | CandidateSource::AliasBound => true,
CandidateSource::CoherenceUnknowable => panic!("uh oh"),
});
}
// If it is still ambiguous we instead just force the whole goal
// to be ambig and wait for inference constraints. See
// tests/ui/traits/next-solver/env-shadows-impls/ambig-env-no-shadow.rs
Certainty::Maybe(cause) => {
debug!(?cause, "force ambiguity");
*candidates = self.forced_ambiguity(cause).into_iter().collect();
}
}
}
}
/// If there are multiple ways to prove a trait or projection goal, we have
/// to somehow try to merge the candidates into one. If that fails, we return
/// ambiguity.
/// Most notably, when proving a trait goal by via a where-bound, we should not
/// normalize via impls which have stricter region constraints than the where-bound:
///
/// ```rust
/// trait Trait<'a> {
/// type Assoc;
/// }
///
/// impl<'a, T: 'a> Trait<'a> for T {
/// type Assoc = u32;
/// }
///
/// fn with_bound<'a, T: Trait<'a>>(_value: T::Assoc) {}
/// ```
///
/// The where-bound of `with_bound` doesn't specify the associated type, so we would
/// only be able to normalize `<T as Trait<'a>>::Assoc` by using the impl. This impl
/// adds a `T: 'a` bound however, which would result in a region error. Given that the
/// user explicitly wrote that `T: Trait<'a>` holds, this is undesirable and we instead
/// treat the alias as rigid.
///
/// See trait-system-refactor-initiative#124 for more details.
#[instrument(level = "debug", skip(self), ret)]
pub(super) fn merge_candidates(&mut self, candidates: Vec<Candidate<I>>) -> QueryResult<I> {
// First try merging all candidates. This is complete and fully sound.
let responses = candidates.iter().map(|c| c.result).collect::<Vec<_>>();
if let Some(result) = self.try_merge_responses(&responses) {
return Ok(result);
} else {
self.flounder(&responses)
}
pub(super) fn merge_candidates(
&mut self,
proven_via: Option<TraitGoalProvenVia>,
candidates: Vec<Candidate<I>>,
) -> QueryResult<I> {
let Some(proven_via) = proven_via else {
// We don't care about overflow. If proving the trait goal overflowed, then
// it's enough to report an overflow error for that, we don't also have to
// overflow during normalization.
return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Ambiguity));
};
let responses: Vec<_> = match proven_via {
// Even when a trait bound has been proven using a where-bound, we
// still need to consider alias-bounds for normalization, see
// tests/ui/next-solver/alias-bound-shadowed-by-env.rs.
//
// FIXME(const_trait_impl): should this behavior also be used by
// constness checking. Doing so is *at least theoretically* breaking,
// see github.com/rust-lang/rust/issues/133044#issuecomment-2500709754
TraitGoalProvenVia::ParamEnv | TraitGoalProvenVia::AliasBound => candidates
.iter()
.filter(|c| {
matches!(c.source, CandidateSource::AliasBound | CandidateSource::ParamEnv(_))
})
.map(|c| c.result)
.collect(),
TraitGoalProvenVia::Misc => candidates.iter().map(|c| c.result).collect(),
};
self.try_merge_responses(&responses).map_or_else(|| self.flounder(&responses), Ok)
}
}

8
compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
View file

@ -4,6 +4,7 @@
use rustc_type_ir::fast_reject::DeepRejectCtxt;
use rustc_type_ir::inherent::*;
use rustc_type_ir::lang_items::TraitSolverLangItem;
use rustc_type_ir::solve::inspect::ProbeKind;
use rustc_type_ir::{self as ty, Interner, elaborate};
use tracing::instrument;
@ -391,6 +392,11 @@ where
goal: Goal<I, ty::HostEffectPredicate<I>>,
) -> QueryResult<I> {
let candidates = self.assemble_and_evaluate_candidates(goal);
self.merge_candidates(candidates)
let (_, proven_via) = self.probe(|_| ProbeKind::ShadowedEnvProbing).enter(|ecx| {
let trait_goal: Goal<I, ty::TraitPredicate<I>> =
goal.with(ecx.cx(), goal.predicate.trait_ref);
ecx.compute_trait_goal(trait_goal)
})?;
self.merge_candidates(proven_via, candidates)
}
}

23
compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
View file

@ -18,7 +18,7 @@ use rustc_type_ir::relate::solver_relating::RelateExt;
use rustc_type_ir::{self as ty, Canonical, CanonicalVarValues, InferCtxtLike, Interner};
use tracing::{debug, instrument, trace};
use crate::canonicalizer::{CanonicalizeMode, Canonicalizer};
use crate::canonicalizer::Canonicalizer;
use crate::delegate::SolverDelegate;
use crate::resolve::EagerResolver;
use crate::solve::eval_ctxt::NestedGoals;
@ -60,17 +60,13 @@ where
(goal, opaque_types).fold_with(&mut EagerResolver::new(self.delegate));
let mut orig_values = Default::default();
let canonical = Canonicalizer::canonicalize(
self.delegate,
CanonicalizeMode::Input,
&mut orig_values,
QueryInput {
let canonical =
Canonicalizer::canonicalize_input(self.delegate, &mut orig_values, QueryInput {
goal,
predefined_opaques_in_body: self
.cx()
.mk_predefined_opaques_in_body(PredefinedOpaquesData { opaque_types }),
},
);
});
let query_input = ty::CanonicalQueryInput { canonical, typing_mode: self.typing_mode() };
(orig_values, query_input)
}
@ -148,9 +144,9 @@ where
.region_constraints
.retain(|outlives| outlives.0.as_region().map_or(true, |re| re != outlives.1));
let canonical = Canonicalizer::canonicalize(
let canonical = Canonicalizer::canonicalize_response(
self.delegate,
CanonicalizeMode::Response { max_input_universe: self.max_input_universe },
self.max_input_universe,
&mut Default::default(),
Response {
var_values,
@ -428,12 +424,7 @@ where
let var_values = CanonicalVarValues { var_values: delegate.cx().mk_args(var_values) };
let state = inspect::State { var_values, data };
let state = state.fold_with(&mut EagerResolver::new(delegate));
Canonicalizer::canonicalize(
delegate,
CanonicalizeMode::Response { max_input_universe },
&mut vec![],
state,
)
Canonicalizer::canonicalize_response(delegate, max_input_universe, &mut vec![], state)
}
// FIXME: needs to be pub to be accessed by downstream

2
compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
View file

@ -440,7 +440,7 @@ where
if let Some(kind) = kind.no_bound_vars() {
match kind {
ty::PredicateKind::Clause(ty::ClauseKind::Trait(predicate)) => {
self.compute_trait_goal(Goal { param_env, predicate })
self.compute_trait_goal(Goal { param_env, predicate }).map(|(r, _via)| r)
}
ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(predicate)) => {
self.compute_host_effect_goal(Goal { param_env, predicate })

25
compiler/rustc_next_trait_solver/src/solve/mod.rs
View file

@ -243,22 +243,27 @@ where
.copied()
}
fn bail_with_ambiguity(&mut self, responses: &[CanonicalResponse<I>]) -> CanonicalResponse<I> {
debug_assert!(!responses.is_empty());
if let Certainty::Maybe(maybe_cause) =
responses.iter().fold(Certainty::AMBIGUOUS, |certainty, response| {
certainty.unify_with(response.value.certainty)
})
{
self.make_ambiguous_response_no_constraints(maybe_cause)
} else {
panic!("expected flounder response to be ambiguous")
}
}
/// If we fail to merge responses we flounder and return overflow or ambiguity.
#[instrument(level = "trace", skip(self), ret)]
fn flounder(&mut self, responses: &[CanonicalResponse<I>]) -> QueryResult<I> {
if responses.is_empty() {
return Err(NoSolution);
} else {
Ok(self.bail_with_ambiguity(responses))
}
let Certainty::Maybe(maybe_cause) =
responses.iter().fold(Certainty::AMBIGUOUS, |certainty, response| {
certainty.unify_with(response.value.certainty)
})
else {
panic!("expected flounder response to be ambiguous")
};
Ok(self.make_ambiguous_response_no_constraints(maybe_cause))
}
/// Normalize a type for when it is structurally matched on.

11
compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
View file

@ -88,10 +88,17 @@ where
/// returns `NoSolution`.
#[instrument(level = "trace", skip(self), ret)]
fn normalize_at_least_one_step(&mut self, goal: Goal<I, NormalizesTo<I>>) -> QueryResult<I> {
match goal.predicate.alias.kind(self.cx()) {
let cx = self.cx();
match goal.predicate.alias.kind(cx) {
ty::AliasTermKind::ProjectionTy | ty::AliasTermKind::ProjectionConst => {
let candidates = self.assemble_and_evaluate_candidates(goal);
self.merge_candidates(candidates)
let (_, proven_via) =
self.probe(|_| ProbeKind::ShadowedEnvProbing).enter(|ecx| {
let trait_goal: Goal<I, ty::TraitPredicate<I>> =
goal.with(cx, goal.predicate.alias.trait_ref(cx));
ecx.compute_trait_goal(trait_goal)
})?;
self.merge_candidates(proven_via, candidates)
}
ty::AliasTermKind::InherentTy => self.normalize_inherent_associated_type(goal),
ty::AliasTermKind::OpaqueTy => self.normalize_opaque_type(goal),

93
compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
View file

@ -5,6 +5,7 @@ use rustc_type_ir::data_structures::IndexSet;
use rustc_type_ir::fast_reject::DeepRejectCtxt;
use rustc_type_ir::inherent::*;
use rustc_type_ir::lang_items::TraitSolverLangItem;
use rustc_type_ir::solve::CanonicalResponse;
use rustc_type_ir::visit::TypeVisitableExt as _;
use rustc_type_ir::{self as ty, Interner, TraitPredicate, TypingMode, Upcast as _, elaborate};
use tracing::{instrument, trace};
@ -1147,13 +1148,101 @@ where
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
}
/// How we've proven this trait goal.
///
/// This is used by `NormalizesTo` goals to only normalize
/// by using the same 'kind of candidate' we've used to prove
/// its corresponding trait goal. Most notably, we do not
/// normalize by using an impl if the trait goal has been
/// proven via a `ParamEnv` candidate.
///
/// This is necessary to avoid unnecessary region constraints,
/// see trait-system-refactor-initiative#125 for more details.
#[derive(Debug, Clone, Copy)]
pub(super) enum TraitGoalProvenVia {
/// We've proven the trait goal by something which is
/// is not a non-global where-bound or an alias-bound.
///
/// This means we don't disable any candidates during
/// normalization.
Misc,
ParamEnv,
AliasBound,
}
impl<D, I> EvalCtxt<'_, D>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
pub(super) fn merge_trait_candidates(
&mut self,
goal: Goal<I, TraitPredicate<I>>,
candidates: Vec<Candidate<I>>,
) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
if let TypingMode::Coherence = self.typing_mode() {
let all_candidates: Vec<_> = candidates.into_iter().map(|c| c.result).collect();
return if let Some(response) = self.try_merge_responses(&all_candidates) {
Ok((response, Some(TraitGoalProvenVia::Misc)))
} else {
self.flounder(&all_candidates).map(|r| (r, None))
};
}
// FIXME: prefer trivial builtin impls
// If there are non-global where-bounds, prefer where-bounds
// (including global ones) over everything else.
let has_non_global_where_bounds = candidates.iter().any(|c| match c.source {
CandidateSource::ParamEnv(idx) => {
let where_bound = goal.param_env.caller_bounds().get(idx);
where_bound.has_bound_vars() || !where_bound.is_global()
}
_ => false,
});
if has_non_global_where_bounds {
let where_bounds: Vec<_> = candidates
.iter()
.filter(|c| matches!(c.source, CandidateSource::ParamEnv(_)))
.map(|c| c.result)
.collect();
return if let Some(response) = self.try_merge_responses(&where_bounds) {
Ok((response, Some(TraitGoalProvenVia::ParamEnv)))
} else {
Ok((self.bail_with_ambiguity(&where_bounds), None))
};
}
if candidates.iter().any(|c| matches!(c.source, CandidateSource::AliasBound)) {
let alias_bounds: Vec<_> = candidates
.iter()
.filter(|c| matches!(c.source, CandidateSource::AliasBound))
.map(|c| c.result)
.collect();
return if let Some(response) = self.try_merge_responses(&alias_bounds) {
Ok((response, Some(TraitGoalProvenVia::AliasBound)))
} else {
Ok((self.bail_with_ambiguity(&alias_bounds), None))
};
}
let all_candidates: Vec<_> = candidates.into_iter().map(|c| c.result).collect();
if let Some(response) = self.try_merge_responses(&all_candidates) {
Ok((response, Some(TraitGoalProvenVia::Misc)))
} else {
self.flounder(&all_candidates).map(|r| (r, None))
}
}
#[instrument(level = "trace", skip(self))]
pub(super) fn compute_trait_goal(
&mut self,
goal: Goal<I, TraitPredicate<I>>,
) -> QueryResult<I> {
) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
let candidates = self.assemble_and_evaluate_candidates(goal);
self.merge_candidates(candidates)
self.merge_trait_candidates(goal, candidates)
}
}

2
compiler/rustc_type_ir/src/inherent.rs
View file

@ -543,7 +543,7 @@ pub trait AdtDef<I: Interner>: Copy + Debug + Hash + Eq {
}
pub trait ParamEnv<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
fn caller_bounds(self) -> impl IntoIterator<Item = I::Clause>;
fn caller_bounds(self) -> impl SliceLike<Item = I::Clause>;
}
pub trait Features<I: Interner>: Copy {

33
tests/crashes/133639.rs
View file

@ -1,33 +0,0 @@
//@ known-bug: #133639
#![feature(with_negative_coherence)]
#![feature(min_specialization)]
#![feature(generic_const_exprs)]
#![crate_type = "lib"]
use std::str::FromStr;
struct a<const b: bool>;
trait c {}
impl<const d: u32> FromStr for e<d>
where
a<{ d <= 2 }>: c,
{
type Err = ();
fn from_str(f: &str) -> Result<Self, Self::Err> {
unimplemented!()
}
}
struct e<const d: u32>;
impl<const d: u32> FromStr for e<d>
where
a<{ d <= 2 }>: c,
{
type Err = ();
fn from_str(f: &str) -> Result<Self, Self::Err> {
unimplemented!()
}
}

19
tests/ui/const-generics/generic_const_exprs/specialization-fuzzing-ice-133639.rs Normal file
View file

@ -0,0 +1,19 @@
//@ check-pass
// Regression test for #133639.
#![feature(with_negative_coherence)]
#![feature(min_specialization)]
#![feature(generic_const_exprs)]
//~^ WARNING the feature `generic_const_exprs` is incomplete
#![crate_type = "lib"]
trait Trait {}
struct A<const B: bool>;
trait C {}
impl<const D: u32> Trait for E<D> where A<{ D <= 2 }>: C {}
struct E<const D: u32>;
impl<const D: u32> Trait for E<D> where A<{ D <= 2 }>: C {}

11
tests/ui/const-generics/generic_const_exprs/specialization-fuzzing-ice-133639.stderr Normal file
View file

@ -0,0 +1,11 @@
warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/specialization-fuzzing-ice-133639.rs:7:12
|
LL | #![feature(generic_const_exprs)]
| ^^^^^^^^^^^^^^^^^^^
|
= note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
= note: `#[warn(incomplete_features)]` on by default
warning: 1 warning emitted

3
tests/ui/const-generics/min_const_generics/param-env-eager-norm-dedup.rs
View file

@ -1,3 +1,6 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
//@ check-pass
// This caused a regression in a crater run in #132325.

9
tests/ui/higher-ranked/trait-bounds/normalize-under-binder/norm-before-method-resolution-opaque-type.next.stderr
View file

@ -1,9 +0,0 @@
error[E0284]: type annotations needed: cannot satisfy `Foo == _`
--> $DIR/norm-before-method-resolution-opaque-type.rs:15:19
|
LL | fn weird_bound<X>(x: &<X as Trait<'static>>::Out<Foo>) -> X
| ^ cannot satisfy `Foo == _`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0284`.

4
tests/ui/higher-ranked/trait-bounds/normalize-under-binder/norm-before-method-resolution-opaque-type.old.stderr
View file

@ -1,12 +1,12 @@
error: item does not constrain `Foo::{opaque#0}`, but has it in its signature
--> $DIR/norm-before-method-resolution-opaque-type.rs:15:4
--> $DIR/norm-before-method-resolution-opaque-type.rs:16:4
|
LL | fn weird_bound<X>(x: &<X as Trait<'static>>::Out<Foo>) -> X
| ^^^^^^^^^^^
|
= note: consider moving the opaque type's declaration and defining uses into a separate module
note: this opaque type is in the signature
--> $DIR/norm-before-method-resolution-opaque-type.rs:13:12
--> $DIR/norm-before-method-resolution-opaque-type.rs:14:12
|
LL | type Foo = impl Sized;
| ^^^^^^^^^^

2
tests/ui/higher-ranked/trait-bounds/normalize-under-binder/norm-before-method-resolution-opaque-type.rs
View file

@ -1,5 +1,6 @@
//@ revisions: old next
//@[next] compile-flags: -Znext-solver
//@[next] check-pass
#![feature(type_alias_impl_trait)]
trait Trait<'a> {
@ -14,7 +15,6 @@ type Foo = impl Sized;
fn weird_bound<X>(x: &<X as Trait<'static>>::Out<Foo>) -> X
//[old]~^ ERROR: item does not constrain
//[next]~^^ ERROR: cannot satisfy `Foo == _`
where
for<'a> X: Trait<'a>,
for<'a> <X as Trait<'a>>::Out<()>: Copy,

5
tests/ui/traits/next-solver/generalize/occurs-check-nested-alias.rs
View file

@ -37,9 +37,4 @@ fn foo<T: Unnormalizable>() {
// result in a cyclic type. However, we can still unify these types by first
// normalizing the inner associated type. Emitting an error here would be incomplete.
drop::<T>(t);
// FIXME(-Znext-solver): This line is necessary due to an unrelated solver bug
// and should get removed in the future.
// https://github.com/rust-lang/trait-system-refactor-initiative/issues/96
drop::<Inv<<T as Unnormalizable>::Assoc>>(u);
}

3
tests/ui/traits/winnowing/global-non-global-env-1.rs
View file

@ -1,3 +1,6 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
//@ check-pass
// A regression test for an edge case of candidate selection

3
tests/ui/traits/winnowing/global-non-global-env-2.rs
View file

@ -1,3 +1,6 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
//@ check-pass
// A regression test for an edge case of candidate selection

3
tests/ui/traits/winnowing/global-non-global-env-3.rs
View file

@ -1,3 +1,6 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
//@ check-pass
// A regression test for an edge case of candidate selection

3
tests/ui/traits/winnowing/global-non-global-env-4.rs
View file

@ -1,3 +1,6 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
//@ check-pass
// A regression test for an edge case of candidate selection