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Rollup merge of #120549 - lcnr:errs-showcase, r=compiler-errors

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modify alias-relate to also normalize ambiguous opaques

allows a bunch of further cleanups and generally simplifies the type system. To handle https://github.com/rust-lang/trait-system-refactor-initiative/issues/8 we'll have to add a some additional complexity to the `(Alias, Infer)` branches in alias-relate, so removing the opaque type special case here is really valuable.

It does worsen `deduce_closure_signature` and friends even more as they now receive an inference variable which is only constrained via an `AliasRelate` goal. These probably have to look into alias relate goals somehow. Leaving that for a future PR as this is something we'll have to tackle regardless.

r? `@compiler-errors`
This commit is contained in:
Matthias Krüger 2024-02-13 17:38:10 +01:00 • committed by GitHub
commit 65ab663266
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23 changed files with 186 additions and 214 deletions
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111
compiler/rustc_trait_selection/src/solve/alias_relate.rs
View file

@ -3,33 +3,27 @@
//! of our more general approach to "lazy normalization".
//!
//! This is done by first normalizing both sides of the goal, ending up in
//! either a concrete type, rigid projection, opaque, or an infer variable.
//! either a concrete type, rigid alias, or an infer variable.
//! These are related further according to the rules below:
//!
//! (1.) If we end up with a rigid projection and a rigid projection, then we
//! relate those projections structurally.
//! (1.) If we end up with two rigid aliases, then we relate them structurally.
//!
//! (2.) If we end up with a rigid projection and an alias, then the opaque will
//! have its hidden type defined to be that rigid projection.
//!
//! (3.) If we end up with an opaque and an opaque, then we assemble two
//! candidates, one defining the LHS to be the hidden type of the RHS, and vice
//! versa.
//!
//! (4.) If we end up with an infer var and an opaque or rigid projection, then
//! (2.) If we end up with an infer var and a rigid alias, then
//! we assign the alias to the infer var.
//!
//! (5.) If we end up with an opaque and a rigid (non-projection) type, then we
//! define the hidden type of the opaque to be the rigid type.
//!
//! (6.) Otherwise, if we end with two rigid (non-projection) or infer types,
//! (3.) Otherwise, if we end with two rigid (non-projection) or infer types,
//! relate them structurally.
//!
//! Subtle: when relating an opaque to another type, we emit a
//! `NormalizesTo(opaque, ?fresh_var)` goal when trying to normalize the opaque.
//! This nested goal starts out as ambiguous and does not actually define the opaque.
//! However, if `?fresh_var` ends up geteting equated to another type, we retry the
//! `NormalizesTo` goal, at which point the opaque is actually defined.
use super::{EvalCtxt, GoalSource};
use rustc_infer::infer::DefineOpaqueTypes;
use rustc_infer::traits::query::NoSolution;
use rustc_middle::traits::solve::{Certainty, Goal, QueryResult};
use rustc_middle::ty;
use rustc_middle::ty::{self, Ty};
impl<'tcx> EvalCtxt<'_, 'tcx> {
#[instrument(level = "debug", skip(self), ret)]
@ -59,37 +53,32 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}
(Some(alias), None) => {
(Some(_), None) => {
if rhs.is_infer() {
self.relate(param_env, lhs, variance, rhs)?;
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
} else if alias.is_opaque(tcx) {
// FIXME: This doesn't account for variance.
self.define_opaque(param_env, alias, rhs)
} else {
Err(NoSolution)
}
}
(None, Some(alias)) => {
(None, Some(_)) => {
if lhs.is_infer() {
self.relate(param_env, lhs, variance, rhs)?;
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
} else if alias.is_opaque(tcx) {
// FIXME: This doesn't account for variance.
self.define_opaque(param_env, alias, lhs)
} else {
Err(NoSolution)
}
}
(Some(alias_lhs), Some(alias_rhs)) => {
self.relate_rigid_alias_or_opaque(param_env, alias_lhs, variance, alias_rhs)
self.relate(param_env, alias_lhs, variance, alias_rhs)?;
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}
}
}
// FIXME: This needs a name that reflects that it's okay to bottom-out with an inference var.
/// Normalize the `term` to equate it later. This does not define opaque types.
/// Normalize the `term` to equate it later.
#[instrument(level = "debug", skip(self, param_env), ret)]
fn try_normalize_term(
&mut self,
@ -98,10 +87,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
) -> Result<Option<ty::Term<'tcx>>, NoSolution> {
match term.unpack() {
ty::TermKind::Ty(ty) => {
// We do no define opaque types here but instead do so in `relate_rigid_alias_or_opaque`.
Ok(self
.try_normalize_ty_recur(param_env, DefineOpaqueTypes::No, 0, ty)
.map(Into::into))
Ok(self.try_normalize_ty_recur(param_env, 0, ty).map(Into::into))
}
ty::TermKind::Const(_) => {
if let Some(alias) = term.to_alias_ty(self.tcx()) {
@ -119,51 +105,34 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
}
}
fn define_opaque(
fn try_normalize_ty_recur(
&mut self,
param_env: ty::ParamEnv<'tcx>,
opaque: ty::AliasTy<'tcx>,
term: ty::Term<'tcx>,
) -> QueryResult<'tcx> {
self.add_goal(
GoalSource::Misc,
Goal::new(self.tcx(), param_env, ty::NormalizesTo { alias: opaque, term }),
);
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}
fn relate_rigid_alias_or_opaque(
&mut self,
param_env: ty::ParamEnv<'tcx>,
lhs: ty::AliasTy<'tcx>,
variance: ty::Variance,
rhs: ty::AliasTy<'tcx>,
) -> QueryResult<'tcx> {
let tcx = self.tcx();
let mut candidates = vec![];
if lhs.is_opaque(tcx) {
candidates.extend(
self.probe_misc_candidate("define-lhs-opaque")
.enter(|ecx| ecx.define_opaque(param_env, lhs, rhs.to_ty(tcx).into())),
);
depth: usize,
ty: Ty<'tcx>,
) -> Option<Ty<'tcx>> {
if !self.tcx().recursion_limit().value_within_limit(depth) {
return None;
}
if rhs.is_opaque(tcx) {
candidates.extend(
self.probe_misc_candidate("define-rhs-opaque")
.enter(|ecx| ecx.define_opaque(param_env, rhs, lhs.to_ty(tcx).into())),
let ty::Alias(_, alias) = *ty.kind() else {
return Some(ty);
};
match self.commit_if_ok(|this| {
let normalized_ty = this.next_ty_infer();
let normalizes_to_goal = Goal::new(
this.tcx(),
param_env,
ty::NormalizesTo { alias, term: normalized_ty.into() },
);
}
candidates.extend(self.probe_misc_candidate("args-relate").enter(|ecx| {
ecx.relate(param_env, lhs, variance, rhs)?;
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}));
if let Some(result) = self.try_merge_responses(&candidates) {
Ok(result)
} else {
self.flounder(&candidates)
this.add_goal(GoalSource::Misc, normalizes_to_goal);
this.try_evaluate_added_goals()?;
let ty = this.resolve_vars_if_possible(normalized_ty);
Ok(this.try_normalize_ty_recur(param_env, depth + 1, ty))
}) {
Ok(ty) => ty,
Err(NoSolution) => Some(ty),
}
}
}

40
compiler/rustc_trait_selection/src/solve/assembly/mod.rs
View file

@ -276,11 +276,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
&mut self,
goal: Goal<'tcx, G>,
) -> Vec<Candidate<'tcx>> {
let Some(normalized_self_ty) =
self.try_normalize_ty(goal.param_env, goal.predicate.self_ty())
let Ok(normalized_self_ty) =
self.structurally_normalize_ty(goal.param_env, goal.predicate.self_ty())
else {
debug!("overflow while evaluating self type");
return self.forced_ambiguity(MaybeCause::Overflow);
return vec![];
};
if normalized_self_ty.is_ty_var() {
@ -635,19 +634,12 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
return;
}
match self.try_normalize_ty(goal.param_env, alias_ty.self_ty()) {
// Recurse on the self type of the projection.
Some(next_self_ty) => {
self.assemble_alias_bound_candidates_recur(next_self_ty, goal, candidates);
}
// Bail if we overflow when normalizing, adding an ambiguous candidate.
None => {
if let Ok(result) =
self.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW)
{
candidates.push(Candidate { source: CandidateSource::AliasBound, result });
}
// Recurse on the self type of the projection.
match self.structurally_normalize_ty(goal.param_env, alias_ty.self_ty()) {
Ok(next_self_ty) => {
self.assemble_alias_bound_candidates_recur(next_self_ty, goal, candidates)
}
Err(NoSolution) => {}
}
}
@ -857,19 +849,11 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
let tcx = self.tcx();
let result = self.probe_misc_candidate("coherence unknowable").enter(|ecx| {
let trait_ref = goal.predicate.trait_ref(tcx);
#[derive(Debug)]
struct Overflow;
let lazily_normalize_ty = |ty| match ecx.try_normalize_ty(goal.param_env, ty) {
Some(ty) => Ok(ty),
None => Err(Overflow),
};
let lazily_normalize_ty = |ty| ecx.structurally_normalize_ty(goal.param_env, ty);
match coherence::trait_ref_is_knowable(tcx, trait_ref, lazily_normalize_ty) {
Err(Overflow) => {
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW)
}
Ok(Ok(())) => Err(NoSolution),
Ok(Err(_)) => {
match coherence::trait_ref_is_knowable(tcx, trait_ref, lazily_normalize_ty)? {
Ok(()) => Err(NoSolution),
Err(_) => {
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
}
}

79
compiler/rustc_trait_selection/src/solve/mod.rs
View file

@ -15,15 +15,13 @@
//! about it on zulip.
use rustc_hir::def_id::DefId;
use rustc_infer::infer::canonical::{Canonical, CanonicalVarValues};
use rustc_infer::infer::DefineOpaqueTypes;
use rustc_infer::traits::query::NoSolution;
use rustc_middle::infer::canonical::CanonicalVarInfos;
use rustc_middle::traits::solve::{
CanonicalResponse, Certainty, ExternalConstraintsData, Goal, GoalSource, IsNormalizesToHack,
QueryResult, Response,
};
use rustc_middle::traits::Reveal;
use rustc_middle::ty::{self, OpaqueTypeKey, Ty, TyCtxt, UniverseIndex};
use rustc_middle::ty::{self, AliasRelationDirection, Ty, TyCtxt, UniverseIndex};
use rustc_middle::ty::{
CoercePredicate, RegionOutlivesPredicate, SubtypePredicate, TypeOutlivesPredicate,
};
@ -267,71 +265,32 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
Ok(self.make_ambiguous_response_no_constraints(maybe_cause))
}
/// Normalize a type when it is structually matched on.
/// Normalize a type for when it is structurally matched on.
///
/// In nearly all cases this function must be used before matching on a type.
/// This function is necessary in nearly all cases before matching on a type.
/// Not doing so is likely to be incomplete and therefore unsound during
/// coherence.
#[instrument(level = "debug", skip(self), ret)]
fn try_normalize_ty(
fn structurally_normalize_ty(
&mut self,
param_env: ty::ParamEnv<'tcx>,
ty: Ty<'tcx>,
) -> Option<Ty<'tcx>> {
self.try_normalize_ty_recur(param_env, DefineOpaqueTypes::Yes, 0, ty)
}
fn try_normalize_ty_recur(
&mut self,
param_env: ty::ParamEnv<'tcx>,
define_opaque_types: DefineOpaqueTypes,
depth: usize,
ty: Ty<'tcx>,
) -> Option<Ty<'tcx>> {
if !self.tcx().recursion_limit().value_within_limit(depth) {
return None;
}
let ty::Alias(kind, alias) = *ty.kind() else {
return Some(ty);
};
// We do no always define opaque types eagerly to allow non-defining uses
// in the defining scope. However, if we can unify this opaque to an existing
// opaque, then we should attempt to eagerly reveal the opaque, and we fall
// through.
if let DefineOpaqueTypes::No = define_opaque_types
&& let Reveal::UserFacing = param_env.reveal()
&& let ty::Opaque = kind
&& let Some(def_id) = alias.def_id.as_local()
&& self.can_define_opaque_ty(def_id)
{
if self
.unify_existing_opaque_tys(
param_env,
OpaqueTypeKey { def_id, args: alias.args },
self.next_ty_infer(),
)
.is_empty()
{
return Some(ty);
}
}
match self.commit_if_ok(|this| {
let normalized_ty = this.next_ty_infer();
let normalizes_to_goal = Goal::new(
this.tcx(),
) -> Result<Ty<'tcx>, NoSolution> {
if let ty::Alias(..) = ty.kind() {
let normalized_ty = self.next_ty_infer();
let alias_relate_goal = Goal::new(
self.tcx(),
param_env,
ty::NormalizesTo { alias, term: normalized_ty.into() },
ty::PredicateKind::AliasRelate(
ty.into(),
normalized_ty.into(),
AliasRelationDirection::Equate,
),
);
this.add_goal(GoalSource::Misc, normalizes_to_goal);
this.try_evaluate_added_goals()?;
let ty = this.resolve_vars_if_possible(normalized_ty);
Ok(this.try_normalize_ty_recur(param_env, define_opaque_types, depth + 1, ty))
}) {
Ok(ty) => ty,
Err(NoSolution) => Some(ty),
self.add_goal(GoalSource::Misc, alias_relate_goal);
self.try_evaluate_added_goals()?;
Ok(self.resolve_vars_if_possible(normalized_ty))
} else {
Ok(ty)
}
}
}

20
compiler/rustc_trait_selection/src/solve/normalizes_to/opaques.rs
View file

@ -58,21 +58,11 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
}
}
let expected = match self.try_normalize_ty(goal.param_env, expected) {
Some(ty) => {
if ty.is_ty_var() {
return self.evaluate_added_goals_and_make_canonical_response(
Certainty::AMBIGUOUS,
);
} else {
ty
}
}
None => {
return self
.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW);
}
};
let expected = self.structurally_normalize_ty(goal.param_env, expected)?;
if expected.is_ty_var() {
return self
.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS);
}
// Otherwise, define a new opaque type
self.insert_hidden_type(opaque_type_key, goal.param_env, expected)?;

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

@ -584,11 +584,11 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
let a_ty = goal.predicate.self_ty();
// We need to normalize the b_ty since it's matched structurally
// in the other functions below.
let b_ty = match ecx
.try_normalize_ty(goal.param_env, goal.predicate.trait_ref.args.type_at(1))
{
Some(b_ty) => b_ty,
None => return vec![misc_candidate(ecx, Certainty::OVERFLOW)],
let Ok(b_ty) = ecx.structurally_normalize_ty(
goal.param_env,
goal.predicate.trait_ref.args.type_at(1),
) else {
return vec![];
};
let goal = goal.with(ecx.tcx(), (a_ty, b_ty));