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Normalize the RHS of an unsize goal

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This commit is contained in:
Michael Goulet 2023-07-06 02:53:21 +00:00
parent 23405bb123
commit 7e66c0b7ed
5 changed files with 169 additions and 69 deletions
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6
compiler/rustc_middle/src/traits/solve/inspect.rs
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@ -73,8 +73,12 @@ pub struct GoalCandidate<'tcx> {
pub enum CandidateKind<'tcx> {
/// Probe entered when normalizing the self ty during candidate assembly
NormalizedSelfTyAssembly,
DynUpcastingAssembly,
/// A normal candidate for proving a goal
Candidate { name: String, result: QueryResult<'tcx> },
Candidate {
name: String,
result: QueryResult<'tcx>,
},
}
impl Debug for GoalCandidate<'_> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {

3
compiler/rustc_middle/src/traits/solve/inspect/format.rs
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@ -100,6 +100,9 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
CandidateKind::NormalizedSelfTyAssembly => {
writeln!(self.f, "NORMALIZING SELF TY FOR ASSEMBLY:")
}
CandidateKind::DynUpcastingAssembly => {
writeln!(self.f, "ASSEMBLING CANDIDATES FOR DYN UPCASTING:")
}
CandidateKind::Candidate { name, result } => {
writeln!(self.f, "CANDIDATE {}: {:?}", name, result)
}

10
compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
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@ -330,9 +330,13 @@ fn rematch_unsize<'tcx>(
mut nested: Vec<PredicateObligation<'tcx>>,
) -> SelectionResult<'tcx, Selection<'tcx>> {
let tcx = infcx.tcx;
let a_ty = goal.predicate.self_ty();
let b_ty = goal.predicate.trait_ref.args.type_at(1);
let a_ty = structurally_normalize(goal.predicate.self_ty(), infcx, goal.param_env, &mut nested);
let b_ty = structurally_normalize(
goal.predicate.trait_ref.args.type_at(1),
infcx,
goal.param_env,
&mut nested,
);
match (a_ty.kind(), b_ty.kind()) {
(_, &ty::Dynamic(data, region, ty::Dyn)) => {
// Check that the type implements all of the predicates of the def-id.

198
compiler/rustc_trait_selection/src/solve/trait_goals.rs
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@ -1,12 +1,14 @@
//! Dealing with trait goals, i.e. `T: Trait<'a, U>`.
use super::assembly::{self, structural_traits};
use super::search_graph::OverflowHandler;
use super::{EvalCtxt, SolverMode};
use rustc_hir::def_id::DefId;
use rustc_hir::{LangItem, Movability};
use rustc_infer::traits::query::NoSolution;
use rustc_infer::traits::util::supertraits;
use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
use rustc_middle::traits::solve::inspect::CandidateKind;
use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, MaybeCause, QueryResult};
use rustc_middle::traits::Reveal;
use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, TreatProjections};
use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
@ -376,11 +378,18 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
let tcx = ecx.tcx();
let a_ty = goal.predicate.self_ty();
let b_ty = goal.predicate.trait_ref.args.type_at(1);
if b_ty.is_ty_var() {
return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS);
}
ecx.probe_candidate("builtin unsize").enter(|ecx| {
let Some(b_ty) = ecx.normalize_non_self_ty(b_ty, goal.param_env)? else {
return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Maybe(
MaybeCause::Overflow,
));
};
match (a_ty.kind(), b_ty.kind()) {
(_, ty::Infer(ty::TyVar(_))) => {
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
}
// Trait upcasting, or `dyn Trait + Auto + 'a` -> `dyn Trait + 'b`
(&ty::Dynamic(_, _, ty::Dyn), &ty::Dynamic(_, _, ty::Dyn)) => {
// Dyn upcasting is handled separately, since due to upcasting,
@ -489,74 +498,90 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
let tcx = ecx.tcx();
let a_ty = goal.predicate.self_ty();
let b_ty = goal.predicate.trait_ref.args.type_at(1);
let ty::Dynamic(a_data, a_region, ty::Dyn) = *a_ty.kind() else {
return vec![];
};
let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else {
return vec![];
};
// Need to wrap in a probe since `normalize_non_self_ty` has side-effects.
ecx.probe(|_| CandidateKind::DynUpcastingAssembly).enter(|ecx| {
let a_ty = goal.predicate.self_ty();
let b_ty = goal.predicate.trait_ref.args.type_at(1);
let ty::Dynamic(a_data, a_region, ty::Dyn) = *a_ty.kind() else {
return vec![];
};
// All of a's auto traits need to be in b's auto traits.
let auto_traits_compatible =
b_data.auto_traits().all(|b| a_data.auto_traits().any(|a| a == b));
if !auto_traits_compatible {
return vec![];
}
// We don't care about `ty::Infer` here or errors here, since we'll
// register an ambiguous/error response in the other unsize candidate
// assembly function.
let Ok(Some(b_ty)) = ecx.normalize_non_self_ty(b_ty, goal.param_env) else {
return vec![];
};
let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else {
return vec![];
};
let mut unsize_dyn_to_principal = |principal: Option<ty::PolyExistentialTraitRef<'tcx>>| {
ecx.probe_candidate("upcast dyn to principle").enter(|ecx| -> Result<_, NoSolution> {
// Require that all of the trait predicates from A match B, except for
// the auto traits. We do this by constructing a new A type with B's
// auto traits, and equating these types.
let new_a_data = principal
.into_iter()
.map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait))
.chain(a_data.iter().filter(|a| {
matches!(a.skip_binder(), ty::ExistentialPredicate::Projection(_))
}))
.chain(
b_data
.auto_traits()
.map(ty::ExistentialPredicate::AutoTrait)
.map(ty::Binder::dummy),
);
let new_a_data = tcx.mk_poly_existential_predicates_from_iter(new_a_data);
let new_a_ty = Ty::new_dynamic(tcx, new_a_data, b_region, ty::Dyn);
// We also require that A's lifetime outlives B's lifetime.
ecx.eq(goal.param_env, new_a_ty, b_ty)?;
ecx.add_goal(
goal.with(tcx, ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region))),
);
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
};
let mut responses = vec![];
// If the principal def ids match (or are both none), then we're not doing
// trait upcasting. We're just removing auto traits (or shortening the lifetime).
if a_data.principal_def_id() == b_data.principal_def_id() {
if let Ok(response) = unsize_dyn_to_principal(a_data.principal()) {
responses.push(response);
// All of a's auto traits need to be in b's auto traits.
let auto_traits_compatible =
b_data.auto_traits().all(|b| a_data.auto_traits().any(|a| a == b));
if !auto_traits_compatible {
return vec![];
}
} else if let Some(a_principal) = a_data.principal()
&& let Some(b_principal) = b_data.principal()
{
for super_trait_ref in supertraits(tcx, a_principal.with_self_ty(tcx, a_ty)) {
if super_trait_ref.def_id() != b_principal.def_id() {
continue;
}
let erased_trait_ref = super_trait_ref
.map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
if let Ok(response) = unsize_dyn_to_principal(Some(erased_trait_ref)) {
let mut unsize_dyn_to_principal = |principal: Option<
ty::PolyExistentialTraitRef<'tcx>,
>| {
ecx.probe_candidate("upcast dyn to principle").enter(
|ecx| -> Result<_, NoSolution> {
// Require that all of the trait predicates from A match B, except for
// the auto traits. We do this by constructing a new A type with B's
// auto traits, and equating these types.
let new_a_data = principal
.into_iter()
.map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait))
.chain(a_data.iter().filter(|a| {
matches!(a.skip_binder(), ty::ExistentialPredicate::Projection(_))
}))
.chain(
b_data
.auto_traits()
.map(ty::ExistentialPredicate::AutoTrait)
.map(ty::Binder::dummy),
);
let new_a_data = tcx.mk_poly_existential_predicates_from_iter(new_a_data);
let new_a_ty = Ty::new_dynamic(tcx, new_a_data, b_region, ty::Dyn);
// We also require that A's lifetime outlives B's lifetime.
ecx.eq(goal.param_env, new_a_ty, b_ty)?;
ecx.add_goal(goal.with(
tcx,
ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region)),
));
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
},
)
};
let mut responses = vec![];
// If the principal def ids match (or are both none), then we're not doing
// trait upcasting. We're just removing auto traits (or shortening the lifetime).
if a_data.principal_def_id() == b_data.principal_def_id() {
if let Ok(response) = unsize_dyn_to_principal(a_data.principal()) {
responses.push(response);
}
} else if let Some(a_principal) = a_data.principal()
&& let Some(b_principal) = b_data.principal()
{
for super_trait_ref in supertraits(tcx, a_principal.with_self_ty(tcx, a_ty)) {
if super_trait_ref.def_id() != b_principal.def_id() {
continue;
}
let erased_trait_ref = super_trait_ref.map_bound(|trait_ref| {
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
});
if let Ok(response) = unsize_dyn_to_principal(Some(erased_trait_ref)) {
responses.push(response);
}
}
}
}
responses
responses
})
}
fn consider_builtin_discriminant_kind_candidate(
@ -750,4 +775,47 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
let candidates = self.assemble_and_evaluate_candidates(goal);
self.merge_candidates(candidates)
}
/// Normalize a non-self type when it is structually matched on when solving
/// a built-in goal. This is handled already through `assemble_candidates_after_normalizing_self_ty`
/// for the self type, but for other goals, additional normalization of other
/// arguments may be needed to completely implement the semantics of the trait.
///
/// This is required when structurally matching on any trait argument that is
/// not the self type.
fn normalize_non_self_ty(
&mut self,
mut ty: Ty<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Result<Option<Ty<'tcx>>, NoSolution> {
if !matches!(ty.kind(), ty::Alias(..)) {
return Ok(Some(ty));
}
self.repeat_while_none(
|_| Ok(None),
|ecx| {
let ty::Alias(_, projection_ty) = *ty.kind() else {
return Some(Ok(Some(ty)));
};
let normalized_ty = ecx.next_ty_infer();
let normalizes_to_goal = Goal::new(
ecx.tcx(),
param_env,
ty::Binder::dummy(ty::ProjectionPredicate {
projection_ty,
term: normalized_ty.into(),
}),
);
ecx.add_goal(normalizes_to_goal);
if let Err(err) = ecx.try_evaluate_added_goals() {
return Some(Err(err));
}
ty = ecx.resolve_vars_if_possible(normalized_ty);
None
},
)
}
}

21
tests/ui/traits/new-solver/normalize-unsize-rhs.rs Normal file
View File

@ -0,0 +1,21 @@
// compile-flags: -Ztrait-solver=next
// check-pass
trait A {}
trait B: A {}
impl A for usize {}
impl B for usize {}
trait Mirror {
type Assoc: ?Sized;
}
impl<T: ?Sized> Mirror for T {
type Assoc = T;
}
fn main() {
let x = Box::new(1usize) as Box<<dyn B as Mirror>::Assoc>;
let y = x as Box<<dyn A as Mirror>::Assoc>;
}