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Auto merge of #120544 - BoxyUwU:enter_forall, r=lcnr

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Introduce `enter_forall` to supercede `instantiate_binder_with_placeholders`

r? `@lcnr`

Long term we'd like to experiment with decrementing the universe count after "exiting" binders so that we do not end up creating infer vars in non-root universes even when they logically reside in the root universe. The fact that we dont do this currently results in a number of issues in the new trait solver where we consider goals to be ambiguous because otherwise it would require lowering the universe of an infer var. i.e. the goal  `?x.0 eq <T as Trait<?y.1>>::Assoc` where the alias is rigid would not be able to instantiate `?x` with the alias as there would be a universe error.

This PR is the first-ish sort of step towards being able to implement this as eventually we would want to decrement the universe in `enter_forall`. Unfortunately its Difficult to actually implement decrementing universes nicely so this is a separate step which moves us closer to the long term goal ✨
This commit is contained in:
bors 2024-02-08 16:42:56 +00:00
commit c29082fe7d
21 changed files with 629 additions and 549 deletions
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189
compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
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@ -77,101 +77,104 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
for (pred, pred_span) in
cx.tcx.explicit_item_bounds(def_id).instantiate_identity_iter_copied()
{
let predicate = infcx.instantiate_binder_with_placeholders(pred.kind());
let ty::ClauseKind::Projection(proj) = predicate else {
continue;
};
// Only check types, since those are the only things that may
// have opaques in them anyways.
let Some(proj_term) = proj.term.ty() else { continue };
// HACK: `impl Trait<Assoc = impl Trait2>` from an RPIT is "ok"...
if let ty::Alias(ty::Opaque, opaque_ty) = *proj_term.kind()
&& cx.tcx.parent(opaque_ty.def_id) == def_id
&& matches!(
opaque.origin,
hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_)
)
{
continue;
}
// HACK: `async fn() -> Self` in traits is "ok"...
// This is not really that great, but it's similar to why the `-> Self`
// return type is well-formed in traits even when `Self` isn't sized.
if let ty::Param(param_ty) = *proj_term.kind()
&& param_ty.name == kw::SelfUpper
&& matches!(opaque.origin, hir::OpaqueTyOrigin::AsyncFn(_))
&& opaque.in_trait
{
continue;
}
let proj_ty =
Ty::new_projection(cx.tcx, proj.projection_ty.def_id, proj.projection_ty.args);
// For every instance of the projection type in the bounds,
// replace them with the term we're assigning to the associated
// type in our opaque type.
let proj_replacer = &mut BottomUpFolder {
tcx: cx.tcx,
ty_op: |ty| if ty == proj_ty { proj_term } else { ty },
lt_op: |lt| lt,
ct_op: |ct| ct,
};
// For example, in `impl Trait<Assoc = impl Send>`, for all of the bounds on `Assoc`,
// e.g. `type Assoc: OtherTrait`, replace `<impl Trait as Trait>::Assoc: OtherTrait`
// with `impl Send: OtherTrait`.
for (assoc_pred, assoc_pred_span) in cx
.tcx
.explicit_item_bounds(proj.projection_ty.def_id)
.iter_instantiated_copied(cx.tcx, proj.projection_ty.args)
{
let assoc_pred = assoc_pred.fold_with(proj_replacer);
let Ok(assoc_pred) = traits::fully_normalize(
infcx,
traits::ObligationCause::dummy(),
cx.param_env,
assoc_pred,
) else {
continue;
infcx.enter_forall(pred.kind(), |predicate| {
let ty::ClauseKind::Projection(proj) = predicate else {
return;
};
// If that predicate doesn't hold modulo regions (but passed during type-check),
// then we must've taken advantage of the hack in `project_and_unify_types` where
// we replace opaques with inference vars. Emit a warning!
if !infcx.predicate_must_hold_modulo_regions(&traits::Obligation::new(
cx.tcx,
traits::ObligationCause::dummy(),
cx.param_env,
assoc_pred,
)) {
// If it's a trait bound and an opaque that doesn't satisfy it,
// then we can emit a suggestion to add the bound.
let add_bound = match (proj_term.kind(), assoc_pred.kind().skip_binder()) {
(
ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }),
ty::ClauseKind::Trait(trait_pred),
) => Some(AddBound {
suggest_span: cx.tcx.def_span(*def_id).shrink_to_hi(),
trait_ref: trait_pred.print_modifiers_and_trait_path(),
}),
_ => None,
};
cx.emit_span_lint(
OPAQUE_HIDDEN_INFERRED_BOUND,
pred_span,
OpaqueHiddenInferredBoundLint {
ty: Ty::new_opaque(
cx.tcx,
def_id,
ty::GenericArgs::identity_for_item(cx.tcx, def_id),
),
proj_ty: proj_term,
assoc_pred_span,
add_bound,
},
);
// Only check types, since those are the only things that may
// have opaques in them anyways.
let Some(proj_term) = proj.term.ty() else { return };
// HACK: `impl Trait<Assoc = impl Trait2>` from an RPIT is "ok"...
if let ty::Alias(ty::Opaque, opaque_ty) = *proj_term.kind()
&& cx.tcx.parent(opaque_ty.def_id) == def_id
&& matches!(
opaque.origin,
hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_)
)
{
return;
}
}
// HACK: `async fn() -> Self` in traits is "ok"...
// This is not really that great, but it's similar to why the `-> Self`
// return type is well-formed in traits even when `Self` isn't sized.
if let ty::Param(param_ty) = *proj_term.kind()
&& param_ty.name == kw::SelfUpper
&& matches!(opaque.origin, hir::OpaqueTyOrigin::AsyncFn(_))
&& opaque.in_trait
{
return;
}
let proj_ty =
Ty::new_projection(cx.tcx, proj.projection_ty.def_id, proj.projection_ty.args);
// For every instance of the projection type in the bounds,
// replace them with the term we're assigning to the associated
// type in our opaque type.
let proj_replacer = &mut BottomUpFolder {
tcx: cx.tcx,
ty_op: |ty| if ty == proj_ty { proj_term } else { ty },
lt_op: |lt| lt,
ct_op: |ct| ct,
};
// For example, in `impl Trait<Assoc = impl Send>`, for all of the bounds on `Assoc`,
// e.g. `type Assoc: OtherTrait`, replace `<impl Trait as Trait>::Assoc: OtherTrait`
// with `impl Send: OtherTrait`.
for (assoc_pred, assoc_pred_span) in cx
.tcx
.explicit_item_bounds(proj.projection_ty.def_id)
.iter_instantiated_copied(cx.tcx, proj.projection_ty.args)
{
let assoc_pred = assoc_pred.fold_with(proj_replacer);
let Ok(assoc_pred) = traits::fully_normalize(
infcx,
traits::ObligationCause::dummy(),
cx.param_env,
assoc_pred,
) else {
continue;
};
// If that predicate doesn't hold modulo regions (but passed during type-check),
// then we must've taken advantage of the hack in `project_and_unify_types` where
// we replace opaques with inference vars. Emit a warning!
if !infcx.predicate_must_hold_modulo_regions(&traits::Obligation::new(
cx.tcx,
traits::ObligationCause::dummy(),
cx.param_env,
assoc_pred,
)) {
// If it's a trait bound and an opaque that doesn't satisfy it,
// then we can emit a suggestion to add the bound.
let add_bound = match (proj_term.kind(), assoc_pred.kind().skip_binder()) {
(
ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }),
ty::ClauseKind::Trait(trait_pred),
) => Some(AddBound {
suggest_span: cx.tcx.def_span(*def_id).shrink_to_hi(),
trait_ref: trait_pred.print_modifiers_and_trait_path(),
}),
_ => None,
};
cx.emit_span_lint(
OPAQUE_HIDDEN_INFERRED_BOUND,
pred_span,
OpaqueHiddenInferredBoundLint {
ty: Ty::new_opaque(
cx.tcx,
def_id,
ty::GenericArgs::identity_for_item(cx.tcx, def_id),
),
proj_ty: proj_term,
assoc_pred_span,
add_bound,
},
);
}
}
});
}
}
}