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NormalizesTo return nested goals

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This commit is contained in:
lcnr 2024-03-18 15:29:09 +01:00
parent 33c274f658
commit f26e1e8b63
13 changed files with 172 additions and 93 deletions
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42
compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
View file

@ -9,6 +9,7 @@
//!
//! [c]: https://rustc-dev-guide.rust-lang.org/solve/canonicalization.html
use super::{CanonicalInput, Certainty, EvalCtxt, Goal};
use crate::solve::eval_ctxt::NestedGoals;
use crate::solve::{
inspect, response_no_constraints_raw, CanonicalResponse, QueryResult, Response,
};
@ -19,6 +20,7 @@ use rustc_infer::infer::canonical::CanonicalVarValues;
use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints};
use rustc_infer::infer::resolve::EagerResolver;
use rustc_infer::infer::{InferCtxt, InferOk};
use rustc_infer::traits::solve::NestedNormalizationGoals;
use rustc_middle::infer::canonical::Canonical;
use rustc_middle::traits::query::NoSolution;
use rustc_middle::traits::solve::{
@ -93,13 +95,26 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
previous call to `try_evaluate_added_goals!`"
);
let certainty = certainty.unify_with(goals_certainty);
let var_values = self.var_values;
let external_constraints = self.compute_external_query_constraints()?;
// When normalizing, we've replaced the expected term with an unconstrained
// inference variable. This means that we dropped information which could
// have been important. We handle this by instead returning the nested goals
// to the caller, where they are then handled.
//
// As we return all ambiguous nested goals, we can ignore the certainty returned
// by `try_evaluate_added_goals()`.
let (certainty, normalization_nested_goals) = if self.is_normalizes_to_goal {
let NestedGoals { normalizes_to_goals, goals } = std::mem::take(&mut self.nested_goals);
assert!(normalizes_to_goals.is_empty());
(certainty, NestedNormalizationGoals(goals))
} else {
let certainty = certainty.unify_with(goals_certainty);
(certainty, NestedNormalizationGoals::empty())
};
let external_constraints =
self.compute_external_query_constraints(normalization_nested_goals)?;
let (var_values, mut external_constraints) =
(var_values, external_constraints).fold_with(&mut EagerResolver::new(self.infcx));
(self.var_values, external_constraints).fold_with(&mut EagerResolver::new(self.infcx));
// Remove any trivial region constraints once we've resolved regions
external_constraints
.region_constraints
@ -146,6 +161,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
#[instrument(level = "debug", skip(self), ret)]
fn compute_external_query_constraints(
&self,
normalization_nested_goals: NestedNormalizationGoals<'tcx>,
) -> Result<ExternalConstraintsData<'tcx>, NoSolution> {
// We only check for leaks from universes which were entered inside
// of the query.
@ -176,7 +192,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
self.predefined_opaques_in_body.opaque_types.iter().all(|(pa, _)| pa != a)
});
Ok(ExternalConstraintsData { region_constraints, opaque_types })
Ok(ExternalConstraintsData { region_constraints, opaque_types, normalization_nested_goals })
}
/// After calling a canonical query, we apply the constraints returned
@ -185,13 +201,14 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
/// This happens in three steps:
/// - we instantiate the bound variables of the query response
/// - we unify the `var_values` of the response with the `original_values`
/// - we apply the `external_constraints` returned by the query
/// - we apply the `external_constraints` returned by the query, returning
/// the `normalization_nested_goals`
pub(super) fn instantiate_and_apply_query_response(
&mut self,
param_env: ty::ParamEnv<'tcx>,
original_values: Vec<ty::GenericArg<'tcx>>,
response: CanonicalResponse<'tcx>,
) -> Certainty {
) -> (NestedNormalizationGoals<'tcx>, Certainty) {
let instantiation = Self::compute_query_response_instantiation_values(
self.infcx,
&original_values,
@ -203,11 +220,14 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
Self::unify_query_var_values(self.infcx, param_env, &original_values, var_values);
let ExternalConstraintsData { region_constraints, opaque_types } =
external_constraints.deref();
let ExternalConstraintsData {
region_constraints,
opaque_types,
normalization_nested_goals,
} = external_constraints.deref();
self.register_region_constraints(region_constraints);
self.register_new_opaque_types(param_env, opaque_types);
certainty
(normalization_nested_goals.clone(), certainty)
}
/// This returns the canoncial variable values to instantiate the bound variables of

2
compiler/rustc_trait_selection/src/solve/eval_ctxt/commit_if_ok.rs
View file

@ -11,6 +11,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
infcx: self.infcx,
variables: self.variables,
var_values: self.var_values,
is_normalizes_to_goal: self.is_normalizes_to_goal,
predefined_opaques_in_body: self.predefined_opaques_in_body,
max_input_universe: self.max_input_universe,
search_graph: self.search_graph,
@ -25,6 +26,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
infcx: _,
variables: _,
var_values: _,
is_normalizes_to_goal: _,
predefined_opaques_in_body: _,
max_input_universe: _,
search_graph: _,

86
compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs
View file

@ -7,7 +7,7 @@ use rustc_infer::infer::{
BoundRegionConversionTime, DefineOpaqueTypes, InferCtxt, InferOk, TyCtxtInferExt,
};
use rustc_infer::traits::query::NoSolution;
use rustc_infer::traits::solve::MaybeCause;
use rustc_infer::traits::solve::{MaybeCause, NestedNormalizationGoals};
use rustc_infer::traits::ObligationCause;
use rustc_middle::infer::canonical::CanonicalVarInfos;
use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
@ -61,6 +61,14 @@ pub struct EvalCtxt<'a, 'tcx> {
/// The variable info for the `var_values`, only used to make an ambiguous response
/// with no constraints.
variables: CanonicalVarInfos<'tcx>,
/// Whether we're currently computing a `NormalizesTo` goal. Unlike other goals,
/// `NormalizesTo` goals act like functions with the expected term always being
/// fully unconstrained. This would weaken inference however, as the nested goals
/// never get the inference constraints from the actual normalized-to type. Because
/// of this we return any ambiguous nested goals from `NormalizesTo` to the caller
/// when then adds these to its own context. The caller is always an `AliasRelate`
/// goal so this never leaks out of the solver.
is_normalizes_to_goal: bool,
pub(super) var_values: CanonicalVarValues<'tcx>,
predefined_opaques_in_body: PredefinedOpaques<'tcx>,
@ -91,7 +99,7 @@ pub struct EvalCtxt<'a, 'tcx> {
pub(super) inspect: ProofTreeBuilder<'tcx>,
}
#[derive(Debug, Clone)]
#[derive(Default, Debug, Clone)]
pub(super) struct NestedGoals<'tcx> {
/// These normalizes-to goals are treated specially during the evaluation
/// loop. In each iteration we take the RHS of the projection, replace it with
@ -153,6 +161,10 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
self.search_graph.solver_mode()
}
pub(super) fn set_is_normalizes_to_goal(&mut self) {
self.is_normalizes_to_goal = true;
}
/// Creates a root evaluation context and search graph. This should only be
/// used from outside of any evaluation, and other methods should be preferred
/// over using this manually (such as [`InferCtxtEvalExt::evaluate_root_goal`]).
@ -165,8 +177,8 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
let mut search_graph = search_graph::SearchGraph::new(mode);
let mut ecx = EvalCtxt {
search_graph: &mut search_graph,
infcx,
search_graph: &mut search_graph,
nested_goals: NestedGoals::new(),
inspect: ProofTreeBuilder::new_maybe_root(infcx.tcx, generate_proof_tree),
@ -178,6 +190,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
max_input_universe: ty::UniverseIndex::ROOT,
variables: ty::List::empty(),
var_values: CanonicalVarValues::dummy(),
is_normalizes_to_goal: false,
tainted: Ok(()),
};
let result = f(&mut ecx);
@ -231,6 +244,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
infcx,
variables: canonical_input.variables,
var_values,
is_normalizes_to_goal: false,
predefined_opaques_in_body: input.predefined_opaques_in_body,
max_input_universe: canonical_input.max_universe,
search_graph,
@ -317,6 +331,20 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
source: GoalSource,
goal: Goal<'tcx, ty::Predicate<'tcx>>,
) -> Result<(bool, Certainty), NoSolution> {
let (normalization_nested_goals, has_changed, certainty) =
self.evaluate_goal_raw(goal_evaluation_kind, source, goal)?;
assert!(normalization_nested_goals.is_empty());
Ok((has_changed, certainty))
}
/// FIXME(-Znext-solver=coinduction): `_source` is currently unused but will
/// be necessary once we implement the new coinduction approach.
fn evaluate_goal_raw(
&mut self,
goal_evaluation_kind: GoalEvaluationKind,
_source: GoalSource,
goal: Goal<'tcx, ty::Predicate<'tcx>>,
) -> Result<(NestedNormalizationGoals<'tcx>, bool, Certainty), NoSolution> {
let (orig_values, canonical_goal) = self.canonicalize_goal(goal);
let mut goal_evaluation =
self.inspect.new_goal_evaluation(goal, &orig_values, goal_evaluation_kind);
@ -334,12 +362,12 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
Ok(response) => response,
};
let (certainty, has_changed) = self.instantiate_response_discarding_overflow(
goal.param_env,
source,
orig_values,
canonical_response,
);
let (normalization_nested_goals, certainty, has_changed) = self
.instantiate_response_discarding_overflow(
goal.param_env,
orig_values,
canonical_response,
);
self.inspect.goal_evaluation(goal_evaluation);
// FIXME: We previously had an assert here that checked that recomputing
// a goal after applying its constraints did not change its response.
@ -351,47 +379,25 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
// Once we have decided on how to handle trait-system-refactor-initiative#75,
// we should re-add an assert here.
Ok((has_changed, certainty))
Ok((normalization_nested_goals, has_changed, certainty))
}
fn instantiate_response_discarding_overflow(
&mut self,
param_env: ty::ParamEnv<'tcx>,
source: GoalSource,
original_values: Vec<ty::GenericArg<'tcx>>,
response: CanonicalResponse<'tcx>,
) -> (Certainty, bool) {
// The old solver did not evaluate nested goals when normalizing.
// It returned the selection constraints allowing a `Projection`
// obligation to not hold in coherence while avoiding the fatal error
// from overflow.
//
// We match this behavior here by considering all constraints
// from nested goals which are not from where-bounds. We will already
// need to track which nested goals are required by impl where-bounds
// for coinductive cycles, so we simply reuse that here.
//
// While we could consider overflow constraints in more cases, this should
// not be necessary for backcompat and results in better perf. It also
// avoids a potential inconsistency which would otherwise require some
// tracking for root goals as well. See #119071 for an example.
let keep_overflow_constraints = || {
self.search_graph.current_goal_is_normalizes_to()
&& source != GoalSource::ImplWhereBound
};
if let Certainty::Maybe(MaybeCause::Overflow { .. }) = response.value.certainty
&& !keep_overflow_constraints()
{
return (response.value.certainty, false);
) -> (NestedNormalizationGoals<'tcx>, Certainty, bool) {
if let Certainty::Maybe(MaybeCause::Overflow { .. }) = response.value.certainty {
return (NestedNormalizationGoals::empty(), response.value.certainty, false);
}
let has_changed = !response.value.var_values.is_identity_modulo_regions()
|| !response.value.external_constraints.opaque_types.is_empty();
let certainty =
let (normalization_nested_goals, certainty) =
self.instantiate_and_apply_query_response(param_env, original_values, response);
(certainty, has_changed)
(normalization_nested_goals, certainty, has_changed)
}
fn compute_goal(&mut self, goal: Goal<'tcx, ty::Predicate<'tcx>>) -> QueryResult<'tcx> {
@ -494,7 +500,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
/// Goals for the next step get directly added to the nested goals of the `EvalCtxt`.
fn evaluate_added_goals_step(&mut self) -> Result<Option<Certainty>, NoSolution> {
let tcx = self.tcx();
let mut goals = core::mem::replace(&mut self.nested_goals, NestedGoals::new());
let mut goals = core::mem::take(&mut self.nested_goals);
self.inspect.evaluate_added_goals_loop_start();
@ -515,11 +521,13 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
ty::NormalizesTo { alias: goal.predicate.alias, term: unconstrained_rhs },
);
let (_, certainty) = self.evaluate_goal(
let (NestedNormalizationGoals(nested_goals), _, certainty) = self.evaluate_goal_raw(
GoalEvaluationKind::Nested { is_normalizes_to_hack: IsNormalizesToHack::Yes },
GoalSource::Misc,
unconstrained_goal,
)?;
// Add the nested goals from normalization to our own nested goals.
goals.goals.extend(nested_goals);
// Finally, equate the goal's RHS with the unconstrained var.
// We put the nested goals from this into goals instead of

1
compiler/rustc_trait_selection/src/solve/eval_ctxt/probe.rs
View file

@ -24,6 +24,7 @@ where
infcx: outer_ecx.infcx,
variables: outer_ecx.variables,
var_values: outer_ecx.var_values,
is_normalizes_to_goal: outer_ecx.is_normalizes_to_goal,
predefined_opaques_in_body: outer_ecx.predefined_opaques_in_body,
max_input_universe: outer_ecx.max_input_universe,
search_graph: outer_ecx.search_graph,

13
compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
View file

@ -58,12 +58,13 @@ impl<'tcx> InferCtxt<'tcx> {
}
let candidate = candidates.pop().unwrap();
let certainty = ecx.instantiate_and_apply_query_response(
trait_goal.param_env,
orig_values,
candidate.result,
);
let (normalization_nested_goals, certainty) = ecx
.instantiate_and_apply_query_response(
trait_goal.param_env,
orig_values,
candidate.result,
);
assert!(normalization_nested_goals.is_empty());
Ok(Some((candidate, certainty)))
});

14
compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
View file

@ -70,7 +70,19 @@ impl<'a, 'tcx> InspectCandidate<'a, 'tcx> {
instantiated_goals.push(goal);
}
for &goal in &instantiated_goals {
for goal in instantiated_goals.iter().copied() {
// We need to be careful with `NormalizesTo` goals as the
// expected term has to be replaced with an unconstrained
// inference variable.
if let Some(kind) = goal.predicate.kind().no_bound_vars()
&& let ty::PredicateKind::NormalizesTo(predicate) = kind
&& !predicate.alias.is_opaque(infcx.tcx)
{
// FIXME: We currently skip these goals as
// `fn evaluate_root_goal` ICEs if there are any
// `NestedNormalizationGoals`.
continue;
};
let (_, proof_tree) = infcx.evaluate_root_goal(goal, GenerateProofTree::Yes);
let proof_tree = proof_tree.unwrap();
try_visit!(visitor.visit_goal(&InspectGoal::new(

9
compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
View file

@ -32,10 +32,12 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
) -> QueryResult<'tcx> {
let def_id = goal.predicate.def_id();
let def_kind = self.tcx().def_kind(def_id);
if cfg!(debug_assertions) && !matches!(def_kind, DefKind::OpaqueTy) {
assert!(self.term_is_fully_unconstrained(goal));
match def_kind {
DefKind::OpaqueTy => return self.normalize_opaque_type(goal),
_ => self.set_is_normalizes_to_goal(),
}
debug_assert!(self.term_is_fully_unconstrained(goal));
match self.tcx().def_kind(def_id) {
DefKind::AssocTy | DefKind::AssocConst => {
match self.tcx().associated_item(def_id).container {
@ -49,9 +51,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
}
}
DefKind::AnonConst => self.normalize_anon_const(goal),
DefKind::OpaqueTy => self.normalize_opaque_type(goal),
DefKind::TyAlias => self.normalize_weak_type(goal),
kind => bug!("unknown DefKind {} in projection goal: {goal:#?}", kind.descr(def_id)),
kind => bug!("unknown DefKind {} in normalizes-to goal: {goal:#?}", kind.descr(def_id)),
}
}

10
compiler/rustc_trait_selection/src/solve/search_graph.rs
View file

@ -10,7 +10,6 @@ use rustc_index::IndexVec;
use rustc_middle::dep_graph::dep_kinds;
use rustc_middle::traits::solve::CacheData;
use rustc_middle::traits::solve::{CanonicalInput, Certainty, EvaluationCache, QueryResult};
use rustc_middle::ty;
use rustc_middle::ty::TyCtxt;
use rustc_session::Limit;
use std::mem;
@ -175,15 +174,6 @@ impl<'tcx> SearchGraph<'tcx> {
}
}
pub(super) fn current_goal_is_normalizes_to(&self) -> bool {
self.stack.raw.last().map_or(false, |e| {
matches!(
e.input.value.goal.predicate.kind().skip_binder(),
ty::PredicateKind::NormalizesTo(..)
)
})
}
/// Returns the remaining depth allowed for nested goals.
///
/// This is generally simply one less than the current depth.