bjoernager/rust
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more directly handle member constraints

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This commit is contained in:
lcnr 2024-12-19 10:03:34 +01:00
parent 37e74596c0
commit 674c6577a7
4 changed files with 375 additions and 71 deletions
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46
compiler/rustc_borrowck/src/member_constraints.rs
View file

@ -4,10 +4,9 @@ use std::ops::Index;
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::FxIndexMap;
use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::infer::MemberConstraint;
use rustc_middle::ty::{self, Ty};
use rustc_span::Span;
use tracing::debug;
use tracing::instrument;
/// Compactly stores a set of `R0 member of [R1...Rn]` constraints,
/// indexed by the region `R0`.
@ -70,37 +69,42 @@ impl Default for MemberConstraintSet<'_, ty::RegionVid> {
}
impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
pub(crate) fn is_empty(&self) -> bool {
self.constraints.is_empty()
}
/// Pushes a member constraint into the set.
///
/// The input member constraint `m_c` is in the form produced by
/// the `rustc_middle::infer` code.
///
/// The `to_region_vid` callback fn is used to convert the regions
/// within into `RegionVid` format -- it typically consults the
/// `UniversalRegions` data structure that is known to the caller
/// (but which this code is unaware of).
pub(crate) fn push_constraint(
#[instrument(level = "debug", skip(self))]
pub(crate) fn add_member_constraint(
&mut self,
m_c: &MemberConstraint<'tcx>,
mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
key: ty::OpaqueTypeKey<'tcx>,
hidden_ty: Ty<'tcx>,
definition_span: Span,
member_region_vid: ty::RegionVid,
choice_regions: &[ty::RegionVid],
) {
debug!("push_constraint(m_c={:?})", m_c);
let member_region_vid: ty::RegionVid = to_region_vid(m_c.member_region);
let next_constraint = self.first_constraints.get(&member_region_vid).cloned();
let start_index = self.choice_regions.len();
let end_index = start_index + m_c.choice_regions.len();
debug!("push_constraint: member_region_vid={:?}", member_region_vid);
self.choice_regions.extend(choice_regions);
let end_index = self.choice_regions.len();
let constraint_index = self.constraints.push(NllMemberConstraint {
next_constraint,
member_region_vid,
definition_span: m_c.definition_span,
hidden_ty: m_c.hidden_ty,
key: m_c.key,
definition_span,
hidden_ty,
key,
start_index,
end_index,
});
self.first_constraints.insert(member_region_vid, constraint_index);
self.choice_regions.extend(m_c.choice_regions.iter().map(|&r| to_region_vid(r)));
}
// TODO: removed in the next commit
pub(crate) fn push_constraint(
&mut self,
_: &rustc_middle::infer::MemberConstraint<'tcx>,
_: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
) {
}
}

4
compiler/rustc_borrowck/src/region_infer/mod.rs
View file

@ -571,7 +571,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
/// Given a universal region in scope on the MIR, returns the
/// corresponding index.
///
/// (Panics if `r` is not a registered universal region.)
/// Panics if `r` is not a registered universal region, most notably
/// if it is a placeholder. Handling placeholders requires access to the
/// `MirTypeckRegionConstraints`.
pub(crate) fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
self.universal_regions().to_region_vid(r)
}

61
compiler/rustc_borrowck/src/type_check/mod.rs
View file

@ -40,9 +40,7 @@ use rustc_mir_dataflow::points::DenseLocationMap;
use rustc_span::def_id::CRATE_DEF_ID;
use rustc_span::source_map::Spanned;
use rustc_span::{DUMMY_SP, Span, sym};
use rustc_trait_selection::traits::query::type_op::custom::{
CustomTypeOp, scrape_region_constraints,
};
use rustc_trait_selection::traits::query::type_op::custom::scrape_region_constraints;
use rustc_trait_selection::traits::query::type_op::{TypeOp, TypeOpOutput};
use tracing::{debug, instrument, trace};
@ -89,6 +87,7 @@ mod constraint_conversion;
pub(crate) mod free_region_relations;
mod input_output;
pub(crate) mod liveness;
mod opaque_types;
mod relate_tys;
/// Type checks the given `mir` in the context of the inference
@ -179,52 +178,8 @@ pub(crate) fn type_check<'a, 'tcx>(
liveness::generate(&mut typeck, body, &elements, flow_inits, move_data);
let opaque_type_values = infcx
.take_opaque_types()
.into_iter()
.map(|(opaque_type_key, decl)| {
let _: Result<_, ErrorGuaranteed> = typeck.fully_perform_op(
Locations::All(body.span),
ConstraintCategory::OpaqueType,
CustomTypeOp::new(
|ocx| {
ocx.infcx.register_member_constraints(
opaque_type_key,
decl.hidden_type.ty,
decl.hidden_type.span,
);
Ok(())
},
"opaque_type_map",
),
);
let hidden_type = infcx.resolve_vars_if_possible(decl.hidden_type);
trace!("finalized opaque type {:?} to {:#?}", opaque_type_key, hidden_type.ty.kind());
if hidden_type.has_non_region_infer() {
infcx.dcx().span_bug(
decl.hidden_type.span,
format!("could not resolve {:#?}", hidden_type.ty.kind()),
);
}
// Convert all regions to nll vars.
let (opaque_type_key, hidden_type) =
fold_regions(infcx.tcx, (opaque_type_key, hidden_type), |region, _| {
match region.kind() {
ty::ReVar(_) => region,
ty::RePlaceholder(placeholder) => {
typeck.constraints.placeholder_region(infcx, placeholder)
}
_ => ty::Region::new_var(
infcx.tcx,
typeck.universal_regions.to_region_vid(region),
),
}
});
(opaque_type_key, hidden_type)
})
.collect();
let opaque_type_values =
opaque_types::take_opaques_and_register_member_constraints(&mut typeck);
MirTypeckResults { constraints, universal_region_relations, opaque_type_values }
}
@ -955,6 +910,14 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
self.body
}
fn to_region_vid(&mut self, r: ty::Region<'tcx>) -> RegionVid {
if let ty::RePlaceholder(placeholder) = r.kind() {
self.constraints.placeholder_region(self.infcx, placeholder).as_var()
} else {
self.universal_regions.to_region_vid(r)
}
}
fn unsized_feature_enabled(&self) -> bool {
let features = self.tcx().features();
features.unsized_locals() || features.unsized_fn_params()

335
compiler/rustc_borrowck/src/type_check/opaque_types.rs Normal file
View file

@ -0,0 +1,335 @@
use std::iter;
use rustc_data_structures::fx::FxIndexMap;
use rustc_middle::span_bug;
use rustc_middle::ty::fold::fold_regions;
use rustc_middle::ty::{
self, GenericArgKind, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeSuperVisitable,
TypeVisitable, TypeVisitableExt, TypeVisitor,
};
use tracing::{debug, trace};
use super::{MemberConstraintSet, TypeChecker};
/// Once we're done with typechecking the body, we take all the opaque types
/// defined by this function and add their 'member constraints'.
pub(super) fn take_opaques_and_register_member_constraints<'tcx>(
typeck: &mut TypeChecker<'_, 'tcx>,
) -> FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>> {
let infcx = typeck.infcx;
// Annoying: to invoke `typeck.to_region_vid`, we need access to
// `typeck.constraints`, but we also want to be mutating
// `typeck.member_constraints`. For now, just swap out the value
// we want and replace at the end.
let mut member_constraints = std::mem::take(&mut typeck.constraints.member_constraints);
let opaque_types = infcx
.take_opaque_types()
.into_iter()
.map(|(opaque_type_key, decl)| {
let hidden_type = infcx.resolve_vars_if_possible(decl.hidden_type);
register_member_constraints(
typeck,
&mut member_constraints,
opaque_type_key,
hidden_type,
);
trace!("finalized opaque type {:?} to {:#?}", opaque_type_key, hidden_type.ty.kind());
if hidden_type.has_non_region_infer() {
span_bug!(hidden_type.span, "could not resolve {:?}", hidden_type.ty);
}
// Convert all regions to nll vars.
let (opaque_type_key, hidden_type) =
fold_regions(infcx.tcx, (opaque_type_key, hidden_type), |r, _| {
ty::Region::new_var(infcx.tcx, typeck.to_region_vid(r))
});
(opaque_type_key, hidden_type)
})
.collect();
assert!(typeck.constraints.member_constraints.is_empty());
typeck.constraints.member_constraints = member_constraints;
opaque_types
}
/// Given the map `opaque_types` containing the opaque
/// `impl Trait` types whose underlying, hidden types are being
/// inferred, this method adds constraints to the regions
/// appearing in those underlying hidden types to ensure that they
/// at least do not refer to random scopes within the current
/// function. These constraints are not (quite) sufficient to
/// guarantee that the regions are actually legal values; that
/// final condition is imposed after region inference is done.
///
/// # The Problem
///
/// Let's work through an example to explain how it works. Assume
/// the current function is as follows:
///
/// ```text
/// fn foo<'a, 'b>(..) -> (impl Bar<'a>, impl Bar<'b>)
/// ```
///
/// Here, we have two `impl Trait` types whose values are being
/// inferred (the `impl Bar<'a>` and the `impl
/// Bar<'b>`). Conceptually, this is sugar for a setup where we
/// define underlying opaque types (`Foo1`, `Foo2`) and then, in
/// the return type of `foo`, we *reference* those definitions:
///
/// ```text
/// type Foo1<'x> = impl Bar<'x>;
/// type Foo2<'x> = impl Bar<'x>;
/// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. }
/// // ^^^^ ^^
/// // | |
/// // | args
/// // def_id
/// ```
///
/// As indicating in the comments above, each of those references
/// is (in the compiler) basically generic parameters (`args`)
/// applied to the type of a suitable `def_id` (which identifies
/// `Foo1` or `Foo2`).
///
/// Now, at this point in compilation, what we have done is to
/// replace each of the references (`Foo1<'a>`, `Foo2<'b>`) with
/// fresh inference variables C1 and C2. We wish to use the values
/// of these variables to infer the underlying types of `Foo1` and
/// `Foo2`. That is, this gives rise to higher-order (pattern) unification
/// constraints like:
///
/// ```text
/// for<'a> (Foo1<'a> = C1)
/// for<'b> (Foo1<'b> = C2)
/// ```
///
/// For these equation to be satisfiable, the types `C1` and `C2`
/// can only refer to a limited set of regions. For example, `C1`
/// can only refer to `'static` and `'a`, and `C2` can only refer
/// to `'static` and `'b`. The job of this function is to impose that
/// constraint.
///
/// Up to this point, C1 and C2 are basically just random type
/// inference variables, and hence they may contain arbitrary
/// regions. In fact, it is fairly likely that they do! Consider
/// this possible definition of `foo`:
///
/// ```text
/// fn foo<'a, 'b>(x: &'a i32, y: &'b i32) -> (impl Bar<'a>, impl Bar<'b>) {
/// (&*x, &*y)
/// }
/// ```
///
/// Here, the values for the concrete types of the two impl
/// traits will include inference variables:
///
/// ```text
/// &'0 i32
/// &'1 i32
/// ```
///
/// Ordinarily, the subtyping rules would ensure that these are
/// sufficiently large. But since `impl Bar<'a>` isn't a specific
/// type per se, we don't get such constraints by default. This
/// is where this function comes into play. It adds extra
/// constraints to ensure that all the regions which appear in the
/// inferred type are regions that could validly appear.
///
/// This is actually a bit of a tricky constraint in general. We
/// want to say that each variable (e.g., `'0`) can only take on
/// values that were supplied as arguments to the opaque type
/// (e.g., `'a` for `Foo1<'a>`) or `'static`, which is always in
/// scope. We don't have a constraint quite of this kind in the current
/// region checker.
///
/// # The Solution
///
/// We generally prefer to make `<=` constraints, since they
/// integrate best into the region solver. To do that, we find the
/// "minimum" of all the arguments that appear in the args: that
/// is, some region which is less than all the others. In the case
/// of `Foo1<'a>`, that would be `'a` (it's the only choice, after
/// all). Then we apply that as a least bound to the variables
/// (e.g., `'a <= '0`).
///
/// In some cases, there is no minimum. Consider this example:
///
/// ```text
/// fn baz<'a, 'b>() -> impl Trait<'a, 'b> { ... }
/// ```
///
/// Here we would report a more complex "in constraint", like `'r
/// in ['a, 'b, 'static]` (where `'r` is some region appearing in
/// the hidden type).
///
/// # Constrain regions, not the hidden concrete type
///
/// Note that generating constraints on each region `Rc` is *not*
/// the same as generating an outlives constraint on `Tc` itself.
/// For example, if we had a function like this:
///
/// ```
/// # #![feature(type_alias_impl_trait)]
/// # fn main() {}
/// # trait Foo<'a> {}
/// # impl<'a, T> Foo<'a> for (&'a u32, T) {}
/// fn foo<'a, T>(x: &'a u32, y: T) -> impl Foo<'a> {
/// (x, y)
/// }
///
/// // Equivalent to:
/// # mod dummy { use super::*;
/// type FooReturn<'a, T> = impl Foo<'a>;
/// fn foo<'a, T>(x: &'a u32, y: T) -> FooReturn<'a, T> {
/// (x, y)
/// }
/// # }
/// ```
///
/// then the hidden type `Tc` would be `(&'0 u32, T)` (where `'0`
/// is an inference variable). If we generated a constraint that
/// `Tc: 'a`, then this would incorrectly require that `T: 'a` --
/// but this is not necessary, because the opaque type we
/// create will be allowed to reference `T`. So we only generate a
/// constraint that `'0: 'a`.
fn register_member_constraints<'tcx>(
typeck: &mut TypeChecker<'_, 'tcx>,
member_constraints: &mut MemberConstraintSet<'tcx, ty::RegionVid>,
opaque_type_key: OpaqueTypeKey<'tcx>,
OpaqueHiddenType { span, ty: hidden_ty }: OpaqueHiddenType<'tcx>,
) {
let tcx = typeck.tcx();
let hidden_ty = typeck.infcx.resolve_vars_if_possible(hidden_ty);
debug!(?hidden_ty);
let variances = tcx.variances_of(opaque_type_key.def_id);
debug!(?variances);
// For a case like `impl Foo<'a, 'b>`, we would generate a constraint
// `'r in ['a, 'b, 'static]` for each region `'r` that appears in the
// hidden type (i.e., it must be equal to `'a`, `'b`, or `'static`).
//
// `conflict1` and `conflict2` are the two region bounds that we
// detected which were unrelated. They are used for diagnostics.
// Create the set of choice regions: each region in the hidden
// type can be equal to any of the region parameters of the
// opaque type definition.
let fr_static = typeck.universal_regions.fr_static;
let choice_regions: Vec<_> = opaque_type_key
.args
.iter()
.enumerate()
.filter(|(i, _)| variances[*i] == ty::Invariant)
.filter_map(|(_, arg)| match arg.unpack() {
GenericArgKind::Lifetime(r) => Some(typeck.to_region_vid(r)),
GenericArgKind::Type(_) | GenericArgKind::Const(_) => None,
})
.chain(iter::once(fr_static))
.collect();
// FIXME(#42940): This should use the `FreeRegionsVisitor`, but that's
// not currently sound until we have existential regions.
hidden_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
tcx,
op: |r| {
member_constraints.add_member_constraint(
opaque_type_key,
hidden_ty,
span,
typeck.to_region_vid(r),
&choice_regions,
)
},
});
}
/// Visitor that requires that (almost) all regions in the type visited outlive
/// `least_region`. We cannot use `push_outlives_components` because regions in
/// closure signatures are not included in their outlives components. We need to
/// ensure all regions outlive the given bound so that we don't end up with,
/// say, `ReVar` appearing in a return type and causing ICEs when other
/// functions end up with region constraints involving regions from other
/// functions.
///
/// We also cannot use `for_each_free_region` because for closures it includes
/// the regions parameters from the enclosing item.
///
/// We ignore any type parameters because impl trait values are assumed to
/// capture all the in-scope type parameters.
struct ConstrainOpaqueTypeRegionVisitor<'tcx, OP: FnMut(ty::Region<'tcx>)> {
tcx: TyCtxt<'tcx>,
op: OP,
}
impl<'tcx, OP> TypeVisitor<TyCtxt<'tcx>> for ConstrainOpaqueTypeRegionVisitor<'tcx, OP>
where
OP: FnMut(ty::Region<'tcx>),
{
fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(&mut self, t: &ty::Binder<'tcx, T>) {
t.super_visit_with(self);
}
fn visit_region(&mut self, r: ty::Region<'tcx>) {
match *r {
// ignore bound regions, keep visiting
ty::ReBound(_, _) => {}
_ => (self.op)(r),
}
}
fn visit_ty(&mut self, ty: Ty<'tcx>) {
// We're only interested in types involving regions
if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) {
return;
}
match ty.kind() {
ty::Closure(_, args) => {
// Skip lifetime parameters of the enclosing item(s)
for upvar in args.as_closure().upvar_tys() {
upvar.visit_with(self);
}
args.as_closure().sig_as_fn_ptr_ty().visit_with(self);
}
ty::CoroutineClosure(_, args) => {
// Skip lifetime parameters of the enclosing item(s)
for upvar in args.as_coroutine_closure().upvar_tys() {
upvar.visit_with(self);
}
args.as_coroutine_closure().signature_parts_ty().visit_with(self);
}
ty::Coroutine(_, args) => {
// Skip lifetime parameters of the enclosing item(s)
// Also skip the witness type, because that has no free regions.
for upvar in args.as_coroutine().upvar_tys() {
upvar.visit_with(self);
}
args.as_coroutine().return_ty().visit_with(self);
args.as_coroutine().yield_ty().visit_with(self);
args.as_coroutine().resume_ty().visit_with(self);
}
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
// Skip lifetime parameters that are not captures.
let variances = self.tcx.variances_of(*def_id);
for (v, s) in std::iter::zip(variances, args.iter()) {
if *v != ty::Bivariant {
s.visit_with(self);
}
}
}
_ => {
ty.super_visit_with(self);
}
}
}
}