move `ClosureRegionRequirements` to `rustc_borrowck`

6 files changed, 153 insertions, 15 deletions

diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 92519f2aa7b..d4924e1514d 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -36,7 +36,7 @@ use rustc_infer::infer::{
 };
 use rustc_middle::mir::*;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, ParamEnv, RegionVid, TyCtxt, TypingMode};
+use rustc_middle::ty::{self, ParamEnv, RegionVid, Ty, TyCtxt, TypingMode, fold_regions};
 use rustc_middle::{bug, span_bug};
 use rustc_mir_dataflow::impls::{
     EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
@@ -140,6 +140,143 @@ struct PropagatedBorrowCheckResults<'tcx> {
     used_mut_upvars: SmallVec<[FieldIdx; 8]>,
 }
 
+/// After we borrow check a closure, we are left with various
+/// requirements that we have inferred between the free regions that
+/// appear in the closure's signature or on its field types. These
+/// requirements are then verified and proved by the closure's
+/// creating function. This struct encodes those requirements.
+///
+/// The requirements are listed as being between various `RegionVid`. The 0th
+/// region refers to `'static`; subsequent region vids refer to the free
+/// regions that appear in the closure (or coroutine's) type, in order of
+/// appearance. (This numbering is actually defined by the `UniversalRegions`
+/// struct in the NLL region checker. See for example
+/// `UniversalRegions::closure_mapping`.) Note the free regions in the
+/// closure's signature and captures are erased.
+///
+/// Example: If type check produces a closure with the closure args:
+///
+/// ```text
+/// ClosureArgs = [
+///     'a,                                         // From the parent.
+///     'b,
+///     i8,                                         // the "closure kind"
+///     for<'x> fn(&'<erased> &'x u32) -> &'x u32,  // the "closure signature"
+///     &'<erased> String,                          // some upvar
+/// ]
+/// ```
+///
+/// We would "renumber" each free region to a unique vid, as follows:
+///
+/// ```text
+/// ClosureArgs = [
+///     '1,                                         // From the parent.
+///     '2,
+///     i8,                                         // the "closure kind"
+///     for<'x> fn(&'3 &'x u32) -> &'x u32,         // the "closure signature"
+///     &'4 String,                                 // some upvar
+/// ]
+/// ```
+///
+/// Now the code might impose a requirement like `'1: '2`. When an
+/// instance of the closure is created, the corresponding free regions
+/// can be extracted from its type and constrained to have the given
+/// outlives relationship.
+#[derive(Clone, Debug)]
+pub struct ClosureRegionRequirements<'tcx> {
+    /// The number of external regions defined on the closure. In our
+    /// example above, it would be 3 -- one for `'static`, then `'1`
+    /// and `'2`. This is just used for a sanity check later on, to
+    /// make sure that the number of regions we see at the callsite
+    /// matches.
+    pub num_external_vids: usize,
+
+    /// Requirements between the various free regions defined in
+    /// indices.
+    pub outlives_requirements: Vec<ClosureOutlivesRequirement<'tcx>>,
+}
+
+/// Indicates an outlives-constraint between a type or between two
+/// free regions declared on the closure.
+#[derive(Copy, Clone, Debug)]
+pub struct ClosureOutlivesRequirement<'tcx> {
+    // This region or type ...
+    pub subject: ClosureOutlivesSubject<'tcx>,
+
+    // ... must outlive this one.
+    pub outlived_free_region: ty::RegionVid,
+
+    // If not, report an error here ...
+    pub blame_span: Span,
+
+    // ... due to this reason.
+    pub category: ConstraintCategory<'tcx>,
+}
+
+// Make sure this enum doesn't unintentionally grow
+#[cfg(target_pointer_width = "64")]
+rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
+
+/// The subject of a `ClosureOutlivesRequirement` -- that is, the thing
+/// that must outlive some region.
+#[derive(Copy, Clone, Debug)]
+pub enum ClosureOutlivesSubject<'tcx> {
+    /// Subject is a type, typically a type parameter, but could also
+    /// be a projection. Indicates a requirement like `T: 'a` being
+    /// passed to the caller, where the type here is `T`.
+    Ty(ClosureOutlivesSubjectTy<'tcx>),
+
+    /// Subject is a free region from the closure. Indicates a requirement
+    /// like `'a: 'b` being passed to the caller; the region here is `'a`.
+    Region(ty::RegionVid),
+}
+
+/// Represents a `ty::Ty` for use in [`ClosureOutlivesSubject`].
+///
+/// This abstraction is necessary because the type may include `ReVar` regions,
+/// which is what we use internally within NLL code, and they can't be used in
+/// a query response.
+///
+/// DO NOT implement `TypeVisitable` or `TypeFoldable` traits, because this
+/// type is not recognized as a binder for late-bound region.
+#[derive(Copy, Clone, Debug)]
+pub struct ClosureOutlivesSubjectTy<'tcx> {
+    inner: Ty<'tcx>,
+}
+
+impl<'tcx> ClosureOutlivesSubjectTy<'tcx> {
+    /// All regions of `ty` must be of kind `ReVar` and must represent
+    /// universal regions *external* to the closure.
+    pub fn bind(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
+        let inner = fold_regions(tcx, ty, |r, depth| match r.kind() {
+            ty::ReVar(vid) => {
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_usize(vid.index()),
+                    kind: ty::BoundRegionKind::Anon,
+                };
+                ty::Region::new_bound(tcx, depth, br)
+            }
+            _ => bug!("unexpected region in ClosureOutlivesSubjectTy: {r:?}"),
+        });
+
+        Self { inner }
+    }
+
+    pub fn instantiate(
+        self,
+        tcx: TyCtxt<'tcx>,
+        mut map: impl FnMut(ty::RegionVid) -> ty::Region<'tcx>,
+    ) -> Ty<'tcx> {
+        fold_regions(tcx, self.inner, |r, depth| match r.kind() {
+            ty::ReBound(debruijn, br) => {
+                debug_assert_eq!(debruijn, depth);
+                map(ty::RegionVid::from_usize(br.var.index()))
+            }
+            _ => bug!("unexpected region {r:?}"),
+        })
+    }
+}
+
 /// Perform the actual borrow checking.
 ///
 /// Use `consumer_options: None` for the default behavior of returning
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index df2fbaeffe1..8a2a34f207a 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -8,10 +8,7 @@ use std::str::FromStr;
 use polonius_engine::{Algorithm, Output};
 use rustc_index::IndexSlice;
 use rustc_middle::mir::pretty::{PrettyPrintMirOptions, dump_mir_with_options};
-use rustc_middle::mir::{
-    Body, ClosureOutlivesSubject, ClosureRegionRequirements, PassWhere, Promoted, create_dump_file,
-    dump_enabled, dump_mir,
-};
+use rustc_middle::mir::{Body, PassWhere, Promoted, create_dump_file, dump_enabled, dump_mir};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_mir_dataflow::ResultsCursor;
@@ -32,7 +29,10 @@ use crate::polonius::legacy::{
 use crate::region_infer::RegionInferenceContext;
 use crate::type_check::{self, MirTypeckResults};
 use crate::universal_regions::UniversalRegions;
-use crate::{BorrowCheckRootCtxt, BorrowckInferCtxt, polonius, renumber};
+use crate::{
+    BorrowCheckRootCtxt, BorrowckInferCtxt, ClosureOutlivesSubject, ClosureRegionRequirements,
+    polonius, renumber,
+};
 
 /// The output of `nll::compute_regions`. This includes the computed `RegionInferenceContext`, any
 /// closure requirements to propagate, and any generated errors.
diff --git a/compiler/rustc_borrowck/src/polonius/dump.rs b/compiler/rustc_borrowck/src/polonius/dump.rs
index aa64a7c4e2a..9e4ebfa5930 100644
--- a/compiler/rustc_borrowck/src/polonius/dump.rs
+++ b/compiler/rustc_borrowck/src/polonius/dump.rs
@@ -5,7 +5,7 @@ use rustc_index::IndexVec;
 use rustc_middle::mir::pretty::{
     PassWhere, PrettyPrintMirOptions, create_dump_file, dump_enabled, dump_mir_to_writer,
 };
-use rustc_middle::mir::{Body, ClosureRegionRequirements, Location};
+use rustc_middle::mir::{Body, Location};
 use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_mir_dataflow::points::PointIndex;
 use rustc_session::config::MirIncludeSpans;
@@ -17,7 +17,7 @@ use crate::polonius::{
 };
 use crate::region_infer::values::LivenessValues;
 use crate::type_check::Locations;
-use crate::{BorrowckInferCtxt, RegionInferenceContext};
+use crate::{BorrowckInferCtxt, ClosureRegionRequirements, RegionInferenceContext};
 
 /// `-Zdump-mir=polonius` dumps MIR annotated with NLL and polonius specific information.
 pub(crate) fn dump_polonius_mir<'tcx>(
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index 5756a5e7c7c..15a515a501a 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -13,9 +13,8 @@ use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound,
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
 use rustc_middle::bug;
 use rustc_middle::mir::{
-    AnnotationSource, BasicBlock, Body, ClosureOutlivesRequirement, ClosureOutlivesSubject,
-    ClosureOutlivesSubjectTy, ClosureRegionRequirements, ConstraintCategory, Local, Location,
-    ReturnConstraint, TerminatorKind,
+    AnnotationSource, BasicBlock, Body, ConstraintCategory, Local, Location, ReturnConstraint,
+    TerminatorKind,
 };
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, UniverseIndex, fold_regions};
@@ -24,7 +23,6 @@ use rustc_span::hygiene::DesugaringKind;
 use rustc_span::{DUMMY_SP, Span};
 use tracing::{Level, debug, enabled, instrument, trace};
 
-use crate::BorrowckInferCtxt;
 use crate::constraints::graph::{self, NormalConstraintGraph, RegionGraph};
 use crate::constraints::{ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet};
 use crate::dataflow::BorrowIndex;
@@ -37,6 +35,10 @@ use crate::region_infer::values::{LivenessValues, RegionElement, RegionValues, T
 use crate::type_check::free_region_relations::UniversalRegionRelations;
 use crate::type_check::{Locations, MirTypeckRegionConstraints};
 use crate::universal_regions::UniversalRegions;
+use crate::{
+    BorrowckInferCtxt, ClosureOutlivesRequirement, ClosureOutlivesSubject,
+    ClosureOutlivesSubjectTy, ClosureRegionRequirements,
+};
 
 mod dump_mir;
 mod graphviz;
diff --git a/compiler/rustc_borrowck/src/root_cx.rs b/compiler/rustc_borrowck/src/root_cx.rs
index ed9e244f753..13daa5c7221 100644
--- a/compiler/rustc_borrowck/src/root_cx.rs
+++ b/compiler/rustc_borrowck/src/root_cx.rs
@@ -2,12 +2,11 @@ use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::bug;
-use rustc_middle::mir::{ClosureRegionRequirements, ConcreteOpaqueTypes};
 use rustc_middle::ty::{OpaqueHiddenType, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::ErrorGuaranteed;
 use smallvec::SmallVec;
 
-use crate::PropagatedBorrowCheckResults;
+use crate::{ClosureRegionRequirements, ConcreteOpaqueTypes, PropagatedBorrowCheckResults};
 
 /// The shared context used by both the root as well as all its nested
 /// items.
diff --git a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
index 6fbe1db6330..a1fb64e85dc 100644
--- a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
+++ b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
@@ -6,7 +6,6 @@ use rustc_infer::infer::region_constraints::{GenericKind, VerifyBound};
 use rustc_infer::infer::{self, InferCtxt, SubregionOrigin};
 use rustc_infer::traits::query::type_op::DeeplyNormalize;
 use rustc_middle::bug;
-use rustc_middle::mir::{ClosureOutlivesSubject, ClosureRegionRequirements, ConstraintCategory};
 use rustc_middle::ty::{
     self, GenericArgKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, fold_regions,
 };
@@ -18,6 +17,7 @@ use crate::constraints::OutlivesConstraint;
 use crate::region_infer::TypeTest;
 use crate::type_check::{Locations, MirTypeckRegionConstraints};
 use crate::universal_regions::UniversalRegions;
+use crate::{ClosureOutlivesSubject, ClosureRegionRequirements, ConstraintCategory};
 
 pub(crate) struct ConstraintConversion<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,