borrowck typeck children together with their parent

7 files changed, 191 insertions, 135 deletions

diff --git a/compiler/rustc_borrowck/src/consumers.rs b/compiler/rustc_borrowck/src/consumers.rs
index 45cdd232564..1f087b09234 100644
--- a/compiler/rustc_borrowck/src/consumers.rs
+++ b/compiler/rustc_borrowck/src/consumers.rs
@@ -15,6 +15,7 @@ pub use super::polonius::legacy::{
     RichLocation, RustcFacts,
 };
 pub use super::region_infer::RegionInferenceContext;
+use crate::{BorrowCheckRootCtxt, do_mir_borrowck};
 
 /// Options determining the output behavior of [`get_body_with_borrowck_facts`].
 ///
@@ -97,8 +98,9 @@ pub struct BodyWithBorrowckFacts<'tcx> {
 /// *   Polonius is highly unstable, so expect regular changes in its signature or other details.
 pub fn get_body_with_borrowck_facts(
     tcx: TyCtxt<'_>,
-    def: LocalDefId,
+    def_id: LocalDefId,
     options: ConsumerOptions,
 ) -> BodyWithBorrowckFacts<'_> {
-    *super::do_mir_borrowck(tcx, def, Some(options)).1.unwrap()
+    let mut root_cx = BorrowCheckRootCtxt::new(tcx, def_id);
+    *do_mir_borrowck(&mut root_cx, def_id, Some(options)).1.unwrap()
 }
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 240bd20053b..92519f2aa7b 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -21,6 +21,7 @@ use std::cell::RefCell;
 use std::marker::PhantomData;
 use std::ops::{ControlFlow, Deref};
 
+use root_cx::BorrowCheckRootCtxt;
 use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::dominators::Dominators;
@@ -45,7 +46,7 @@ use rustc_mir_dataflow::move_paths::{
 };
 use rustc_mir_dataflow::{Analysis, EntryStates, Results, ResultsVisitor, visit_results};
 use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT};
-use rustc_span::{Span, Symbol};
+use rustc_span::{ErrorGuaranteed, Span, Symbol};
 use smallvec::SmallVec;
 use tracing::{debug, instrument};
 
@@ -73,7 +74,6 @@ mod def_use;
 mod diagnostics;
 mod member_constraints;
 mod nll;
-mod opaque_types;
 mod path_utils;
 mod place_ext;
 mod places_conflict;
@@ -81,6 +81,7 @@ mod polonius;
 mod prefixes;
 mod region_infer;
 mod renumber;
+mod root_cx;
 mod session_diagnostics;
 mod type_check;
 mod universal_regions;
@@ -102,44 +103,64 @@ pub fn provide(providers: &mut Providers) {
     *providers = Providers { mir_borrowck, ..*providers };
 }
 
-fn mir_borrowck(tcx: TyCtxt<'_>, def: LocalDefId) -> &BorrowCheckResult<'_> {
+/// Provider for `query mir_borrowck`. Similar to `typeck`, this must
+/// only be called for typeck roots which will then borrowck all
+/// nested bodies as well.
+fn mir_borrowck(
+    tcx: TyCtxt<'_>,
+    def: LocalDefId,
+) -> Result<&ConcreteOpaqueTypes<'_>, ErrorGuaranteed> {
+    assert!(!tcx.is_typeck_child(def.to_def_id()));
     let (input_body, _) = tcx.mir_promoted(def);
+    debug!("run query mir_borrowck: {}", tcx.def_path_str(def));
+
     let input_body: &Body<'_> = &input_body.borrow();
-    if input_body.should_skip() || input_body.tainted_by_errors.is_some() {
-        debug!("Skipping borrowck because of injected body or tainted body");
-        // Let's make up a borrowck result! Fun times!
-        let result = BorrowCheckResult {
-            concrete_opaque_types: FxIndexMap::default(),
-            closure_requirements: None,
-            used_mut_upvars: SmallVec::new(),
-            tainted_by_errors: input_body.tainted_by_errors,
-        };
-        return tcx.arena.alloc(result);
+    if let Some(guar) = input_body.tainted_by_errors {
+        debug!("Skipping borrowck because of tainted body");
+        Err(guar)
+    } else if input_body.should_skip() {
+        debug!("Skipping borrowck because of injected body");
+        let opaque_types = ConcreteOpaqueTypes(Default::default());
+        Ok(tcx.arena.alloc(opaque_types))
+    } else {
+        let mut root_cx = BorrowCheckRootCtxt::new(tcx, def);
+        let PropagatedBorrowCheckResults { closure_requirements, used_mut_upvars } =
+            do_mir_borrowck(&mut root_cx, def, None).0;
+        debug_assert!(closure_requirements.is_none());
+        debug_assert!(used_mut_upvars.is_empty());
+        root_cx.finalize()
     }
+}
 
-    let borrowck_result = do_mir_borrowck(tcx, def, None).0;
-    debug!("mir_borrowck done");
-
-    tcx.arena.alloc(borrowck_result)
+/// Data propagated to the typeck parent by nested items.
+/// This should always be empty for the typeck root.
+#[derive(Debug)]
+struct PropagatedBorrowCheckResults<'tcx> {
+    closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
+    used_mut_upvars: SmallVec<[FieldIdx; 8]>,
 }
 
 /// Perform the actual borrow checking.
 ///
 /// Use `consumer_options: None` for the default behavior of returning
-/// [`BorrowCheckResult`] only. Otherwise, return [`BodyWithBorrowckFacts`] according
-/// to the given [`ConsumerOptions`].
-#[instrument(skip(tcx), level = "debug")]
+/// [`PropagatedBorrowCheckResults`] only. Otherwise, return [`BodyWithBorrowckFacts`]
+/// according to the given [`ConsumerOptions`].
+///
+/// For nested bodies this should only be called through `root_cx.get_or_insert_nested`.
+#[instrument(skip(root_cx), level = "debug")]
 fn do_mir_borrowck<'tcx>(
-    tcx: TyCtxt<'tcx>,
+    root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     def: LocalDefId,
     consumer_options: Option<ConsumerOptions>,
-) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
+) -> (PropagatedBorrowCheckResults<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
+    let tcx = root_cx.tcx;
     let infcx = BorrowckInferCtxt::new(tcx, def);
     let (input_body, promoted) = tcx.mir_promoted(def);
     let input_body: &Body<'_> = &input_body.borrow();
     let input_promoted: &IndexSlice<_, _> = &promoted.borrow();
     if let Some(e) = input_body.tainted_by_errors {
         infcx.set_tainted_by_errors(e);
+        root_cx.set_tainted_by_errors(e);
     }
 
     let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
@@ -185,13 +206,13 @@ fn do_mir_borrowck<'tcx>(
     // Compute non-lexical lifetimes.
     let nll::NllOutput {
         regioncx,
-        concrete_opaque_types,
         polonius_input,
         polonius_output,
         opt_closure_req,
         nll_errors,
         polonius_diagnostics,
     } = nll::compute_regions(
+        root_cx,
         &infcx,
         free_regions,
         body,
@@ -210,26 +231,19 @@ fn do_mir_borrowck<'tcx>(
     // We also have a `#[rustc_regions]` annotation that causes us to dump
     // information.
     let diags_buffer = &mut BorrowckDiagnosticsBuffer::default();
-    nll::dump_annotation(
-        &infcx,
-        body,
-        &regioncx,
-        &opt_closure_req,
-        &concrete_opaque_types,
-        diags_buffer,
-    );
+    nll::dump_annotation(&infcx, body, &regioncx, &opt_closure_req, diags_buffer);
 
     let movable_coroutine =
-        // The first argument is the coroutine type passed by value
-        if let Some(local) = body.local_decls.raw.get(1)
-        // Get the interior types and args which typeck computed
-        && let ty::Coroutine(def_id, _) = *local.ty.kind()
-        && tcx.coroutine_movability(def_id) == hir::Movability::Movable
-    {
-        true
-    } else {
-        false
-    };
+    // The first argument is the coroutine type passed by value
+    if let Some(local) = body.local_decls.raw.get(1)
+    // Get the interior types and args which typeck computed
+    && let ty::Coroutine(def_id, _) = *local.ty.kind()
+    && tcx.coroutine_movability(def_id) == hir::Movability::Movable
+{
+    true
+} else {
+    false
+};
 
     // While promoteds should mostly be correct by construction, we need to check them for
     // invalid moves to detect moving out of arrays:`struct S; fn main() { &([S][0]); }`.
@@ -240,6 +254,7 @@ fn do_mir_borrowck<'tcx>(
         // this check out of `MirBorrowckCtxt`, actually doing so is far from trivial.
         let move_data = MoveData::gather_moves(promoted_body, tcx, |_| true);
         let mut promoted_mbcx = MirBorrowckCtxt {
+            root_cx,
             infcx: &infcx,
             body: promoted_body,
             move_data: &move_data,
@@ -280,6 +295,7 @@ fn do_mir_borrowck<'tcx>(
     }
 
     let mut mbcx = MirBorrowckCtxt {
+        root_cx,
         infcx: &infcx,
         body,
         move_data: &move_data,
@@ -347,13 +363,13 @@ fn do_mir_borrowck<'tcx>(
 
     debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
     mbcx.lint_unused_mut();
-    let tainted_by_errors = mbcx.emit_errors();
+    if let Some(guar) = mbcx.emit_errors() {
+        mbcx.root_cx.set_tainted_by_errors(guar);
+    }
 
-    let result = BorrowCheckResult {
-        concrete_opaque_types: concrete_opaque_types.into_inner(),
+    let result = PropagatedBorrowCheckResults {
         closure_requirements: opt_closure_req,
         used_mut_upvars: mbcx.used_mut_upvars,
-        tainted_by_errors,
     };
 
     let body_with_facts = if consumer_options.is_some() {
@@ -488,6 +504,7 @@ impl<'tcx> Deref for BorrowckInferCtxt<'tcx> {
 }
 
 struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
+    root_cx: &'a mut BorrowCheckRootCtxt<'tcx>,
     infcx: &'infcx BorrowckInferCtxt<'tcx>,
     body: &'a Body<'tcx>,
     move_data: &'a MoveData<'tcx>,
@@ -1361,11 +1378,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     | AggregateKind::CoroutineClosure(def_id, _)
                     | AggregateKind::Coroutine(def_id, _) => {
                         let def_id = def_id.expect_local();
-                        let BorrowCheckResult { used_mut_upvars, .. } =
-                            self.infcx.tcx.mir_borrowck(def_id);
+                        let used_mut_upvars = self.root_cx.used_mut_upvars(def_id);
                         debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
-                        for field in used_mut_upvars {
-                            self.propagate_closure_used_mut_upvar(&operands[*field]);
+                        // FIXME: We're cloning the `SmallVec` here to avoid borrowing `root_cx`
+                        // when calling `propagate_closure_used_mut_upvar`. This should ideally
+                        // be unnecessary.
+                        for field in used_mut_upvars.clone() {
+                            self.propagate_closure_used_mut_upvar(&operands[field]);
                         }
                     }
                     AggregateKind::Adt(..)
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index 8e7b6f083ac..df2fbaeffe1 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -25,7 +25,6 @@ use tracing::{debug, instrument};
 use crate::borrow_set::BorrowSet;
 use crate::consumers::ConsumerOptions;
 use crate::diagnostics::{BorrowckDiagnosticsBuffer, RegionErrors};
-use crate::opaque_types::ConcreteOpaqueTypes;
 use crate::polonius::PoloniusDiagnosticsContext;
 use crate::polonius::legacy::{
     PoloniusFacts, PoloniusFactsExt, PoloniusLocationTable, PoloniusOutput,
@@ -33,13 +32,12 @@ use crate::polonius::legacy::{
 use crate::region_infer::RegionInferenceContext;
 use crate::type_check::{self, MirTypeckResults};
 use crate::universal_regions::UniversalRegions;
-use crate::{BorrowckInferCtxt, polonius, renumber};
+use crate::{BorrowCheckRootCtxt, BorrowckInferCtxt, polonius, renumber};
 
 /// The output of `nll::compute_regions`. This includes the computed `RegionInferenceContext`, any
 /// closure requirements to propagate, and any generated errors.
 pub(crate) struct NllOutput<'tcx> {
     pub regioncx: RegionInferenceContext<'tcx>,
-    pub concrete_opaque_types: ConcreteOpaqueTypes<'tcx>,
     pub polonius_input: Option<Box<PoloniusFacts>>,
     pub polonius_output: Option<Box<PoloniusOutput>>,
     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
@@ -78,6 +76,7 @@ pub(crate) fn replace_regions_in_mir<'tcx>(
 ///
 /// This may result in errors being reported.
 pub(crate) fn compute_regions<'a, 'tcx>(
+    root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     infcx: &BorrowckInferCtxt<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
@@ -98,8 +97,6 @@ pub(crate) fn compute_regions<'a, 'tcx>(
 
     let location_map = Rc::new(DenseLocationMap::new(body));
 
-    let mut concrete_opaque_types = ConcreteOpaqueTypes::default();
-
     // Run the MIR type-checker.
     let MirTypeckResults {
         constraints,
@@ -107,6 +104,7 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         opaque_type_values,
         polonius_context,
     } = type_check::type_check(
+        root_cx,
         infcx,
         body,
         promoted,
@@ -117,7 +115,6 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         flow_inits,
         move_data,
         Rc::clone(&location_map),
-        &mut concrete_opaque_types,
     );
 
     // Create the region inference context, taking ownership of the
@@ -181,11 +178,10 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         infcx.set_tainted_by_errors(guar);
     }
 
-    regioncx.infer_opaque_types(infcx, opaque_type_values, &mut concrete_opaque_types);
+    regioncx.infer_opaque_types(root_cx, infcx, opaque_type_values);
 
     NllOutput {
         regioncx,
-        concrete_opaque_types,
         polonius_input: polonius_facts.map(Box::new),
         polonius_output,
         opt_closure_req: closure_region_requirements,
@@ -301,7 +297,6 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
-    concrete_opaque_types: &ConcreteOpaqueTypes<'tcx>,
     diagnostics_buffer: &mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>,
 ) {
     let tcx = infcx.tcx;
@@ -318,7 +313,7 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     // better.
 
     let def_span = tcx.def_span(body.source.def_id());
-    let mut err = if let Some(closure_region_requirements) = closure_region_requirements {
+    let err = if let Some(closure_region_requirements) = closure_region_requirements {
         let mut err = infcx.dcx().struct_span_note(def_span, "external requirements");
 
         regioncx.annotate(tcx, &mut err);
@@ -344,9 +339,7 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
         err
     };
 
-    if !concrete_opaque_types.is_empty() {
-        err.note(format!("Inferred opaque type values:\n{concrete_opaque_types:#?}"));
-    }
+    // FIXME(@lcnr): We currently don't dump the inferred hidden types here.
 
     diagnostics_buffer.buffer_non_error(err);
 }
diff --git a/compiler/rustc_borrowck/src/opaque_types.rs b/compiler/rustc_borrowck/src/opaque_types.rs
deleted file mode 100644
index 5c78814abdd..00000000000
--- a/compiler/rustc_borrowck/src/opaque_types.rs
+++ /dev/null
@@ -1,55 +0,0 @@
-use rustc_data_structures::fx::FxIndexMap;
-use rustc_hir::def_id::LocalDefId;
-use rustc_middle::ty::{OpaqueHiddenType, Ty, TyCtxt};
-
-#[derive(Debug, Default)]
-pub(super) struct ConcreteOpaqueTypes<'tcx> {
-    concrete_opaque_types: FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>>,
-}
-
-impl<'tcx> ConcreteOpaqueTypes<'tcx> {
-    pub(super) fn is_empty(&self) -> bool {
-        self.concrete_opaque_types.is_empty()
-    }
-
-    pub(super) fn into_inner(self) -> FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>> {
-        self.concrete_opaque_types
-    }
-
-    /// Insert an opaque type into the list of opaque types defined by this function
-    /// after mapping the hidden type to the generic parameters of the opaque type
-    /// definition.
-    pub(super) fn insert(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        def_id: LocalDefId,
-        hidden_ty: OpaqueHiddenType<'tcx>,
-    ) {
-        // Sometimes two opaque types are the same only after we remap the generic parameters
-        // back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to
-        // `(X, Y)` and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we
-        // only know that once we convert the generic parameters to those of the opaque type.
-        if let Some(prev) = self.concrete_opaque_types.get_mut(&def_id) {
-            if prev.ty != hidden_ty.ty {
-                let (Ok(guar) | Err(guar)) =
-                    prev.build_mismatch_error(&hidden_ty, tcx).map(|d| d.emit());
-                prev.ty = Ty::new_error(tcx, guar);
-            }
-            // Pick a better span if there is one.
-            // FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
-            prev.span = prev.span.substitute_dummy(hidden_ty.span);
-        } else {
-            self.concrete_opaque_types.insert(def_id, hidden_ty);
-        }
-    }
-
-    pub(super) fn extend_from_nested_body(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        nested_body: &FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>>,
-    ) {
-        for (&def_id, &hidden_ty) in nested_body {
-            self.insert(tcx, def_id, hidden_ty);
-        }
-    }
-}
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index a098450352f..5dc21667447 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -10,7 +10,7 @@ use rustc_trait_selection::opaque_types::check_opaque_type_parameter_valid;
 use tracing::{debug, instrument};
 
 use super::RegionInferenceContext;
-use crate::opaque_types::ConcreteOpaqueTypes;
+use crate::BorrowCheckRootCtxt;
 use crate::session_diagnostics::LifetimeMismatchOpaqueParam;
 use crate::universal_regions::RegionClassification;
 
@@ -58,12 +58,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// [rustc-dev-guide chapter]:
     /// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
-    #[instrument(level = "debug", skip(self, infcx), ret)]
+    #[instrument(level = "debug", skip(self, root_cx, infcx), ret)]
     pub(crate) fn infer_opaque_types(
         &self,
+        root_cx: &mut BorrowCheckRootCtxt<'tcx>,
         infcx: &InferCtxt<'tcx>,
         opaque_ty_decls: FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
-        concrete_opaque_types: &mut ConcreteOpaqueTypes<'tcx>,
     ) {
         let mut decls_modulo_regions: FxIndexMap<OpaqueTypeKey<'tcx>, (OpaqueTypeKey<'tcx>, Span)> =
             FxIndexMap::default();
@@ -140,11 +140,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 }
             }
 
-            concrete_opaque_types.insert(
-                infcx.tcx,
+            root_cx.add_concrete_opaque_type(
                 opaque_type_key.def_id,
-                OpaqueHiddenType { ty, span: concrete_type.span },
+                OpaqueHiddenType { span: concrete_type.span, ty },
             );
+
             // Check that all opaque types have the same region parameters if they have the same
             // non-region parameters. This is necessary because within the new solver we perform
             // various query operations modulo regions, and thus could unsoundly select some impls
diff --git a/compiler/rustc_borrowck/src/root_cx.rs b/compiler/rustc_borrowck/src/root_cx.rs
new file mode 100644
index 00000000000..ed9e244f753
--- /dev/null
+++ b/compiler/rustc_borrowck/src/root_cx.rs
@@ -0,0 +1,102 @@
+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;
+
+/// The shared context used by both the root as well as all its nested
+/// items.
+pub(super) struct BorrowCheckRootCtxt<'tcx> {
+    pub tcx: TyCtxt<'tcx>,
+    root_def_id: LocalDefId,
+    concrete_opaque_types: ConcreteOpaqueTypes<'tcx>,
+    nested_bodies: FxHashMap<LocalDefId, PropagatedBorrowCheckResults<'tcx>>,
+    tainted_by_errors: Option<ErrorGuaranteed>,
+}
+
+impl<'tcx> BorrowCheckRootCtxt<'tcx> {
+    pub(super) fn new(tcx: TyCtxt<'tcx>, root_def_id: LocalDefId) -> BorrowCheckRootCtxt<'tcx> {
+        BorrowCheckRootCtxt {
+            tcx,
+            root_def_id,
+            concrete_opaque_types: Default::default(),
+            nested_bodies: Default::default(),
+            tainted_by_errors: None,
+        }
+    }
+
+    /// Collect all defining uses of opaque types inside of this typeck root. This
+    /// expects the hidden type to be mapped to the definition parameters of the opaque
+    /// and errors if we end up with distinct hidden types.
+    pub(super) fn add_concrete_opaque_type(
+        &mut self,
+        def_id: LocalDefId,
+        hidden_ty: OpaqueHiddenType<'tcx>,
+    ) {
+        // Sometimes two opaque types are the same only after we remap the generic parameters
+        // back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to
+        // `(X, Y)` and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we
+        // only know that once we convert the generic parameters to those of the opaque type.
+        if let Some(prev) = self.concrete_opaque_types.0.get_mut(&def_id) {
+            if prev.ty != hidden_ty.ty {
+                let guar = hidden_ty.ty.error_reported().err().unwrap_or_else(|| {
+                    let (Ok(e) | Err(e)) =
+                        prev.build_mismatch_error(&hidden_ty, self.tcx).map(|d| d.emit());
+                    e
+                });
+                prev.ty = Ty::new_error(self.tcx, guar);
+            }
+            // Pick a better span if there is one.
+            // FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
+            prev.span = prev.span.substitute_dummy(hidden_ty.span);
+        } else {
+            self.concrete_opaque_types.0.insert(def_id, hidden_ty);
+        }
+    }
+
+    pub(super) fn set_tainted_by_errors(&mut self, guar: ErrorGuaranteed) {
+        self.tainted_by_errors = Some(guar);
+    }
+
+    fn get_or_insert_nested(&mut self, def_id: LocalDefId) -> &PropagatedBorrowCheckResults<'tcx> {
+        debug_assert_eq!(
+            self.tcx.typeck_root_def_id(def_id.to_def_id()),
+            self.root_def_id.to_def_id()
+        );
+        if !self.nested_bodies.contains_key(&def_id) {
+            let result = super::do_mir_borrowck(self, def_id, None).0;
+            if let Some(prev) = self.nested_bodies.insert(def_id, result) {
+                bug!("unexpected previous nested body: {prev:?}");
+            }
+        }
+
+        self.nested_bodies.get(&def_id).unwrap()
+    }
+
+    pub(super) fn closure_requirements(
+        &mut self,
+        nested_body_def_id: LocalDefId,
+    ) -> &Option<ClosureRegionRequirements<'tcx>> {
+        &self.get_or_insert_nested(nested_body_def_id).closure_requirements
+    }
+
+    pub(super) fn used_mut_upvars(
+        &mut self,
+        nested_body_def_id: LocalDefId,
+    ) -> &SmallVec<[FieldIdx; 8]> {
+        &self.get_or_insert_nested(nested_body_def_id).used_mut_upvars
+    }
+
+    pub(super) fn finalize(self) -> Result<&'tcx ConcreteOpaqueTypes<'tcx>, ErrorGuaranteed> {
+        if let Some(guar) = self.tainted_by_errors {
+            Err(guar)
+        } else {
+            Ok(self.tcx.arena.alloc(self.concrete_opaque_types))
+        }
+    }
+}
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index f6144a25938..a17dff5d271 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -45,7 +45,6 @@ use crate::borrow_set::BorrowSet;
 use crate::constraints::{OutlivesConstraint, OutlivesConstraintSet};
 use crate::diagnostics::UniverseInfo;
 use crate::member_constraints::MemberConstraintSet;
-use crate::opaque_types::ConcreteOpaqueTypes;
 use crate::polonius::legacy::{PoloniusFacts, PoloniusLocationTable};
 use crate::polonius::{PoloniusContext, PoloniusLivenessContext};
 use crate::region_infer::TypeTest;
@@ -53,7 +52,7 @@ use crate::region_infer::values::{LivenessValues, PlaceholderIndex, PlaceholderI
 use crate::session_diagnostics::{MoveUnsized, SimdIntrinsicArgConst};
 use crate::type_check::free_region_relations::{CreateResult, UniversalRegionRelations};
 use crate::universal_regions::{DefiningTy, UniversalRegions};
-use crate::{BorrowckInferCtxt, path_utils};
+use crate::{BorrowCheckRootCtxt, BorrowckInferCtxt, path_utils};
 
 macro_rules! span_mirbug {
     ($context:expr, $elem:expr, $($message:tt)*) => ({
@@ -102,6 +101,7 @@ mod relate_tys;
 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysis
 /// - `location_map` -- map between MIR `Location` and `PointIndex`
 pub(crate) fn type_check<'a, 'tcx>(
+    root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     infcx: &BorrowckInferCtxt<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
@@ -112,7 +112,6 @@ pub(crate) fn type_check<'a, 'tcx>(
     flow_inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     location_map: Rc<DenseLocationMap>,
-    concrete_opaque_types: &mut ConcreteOpaqueTypes<'tcx>,
 ) -> MirTypeckResults<'tcx> {
     let implicit_region_bound = ty::Region::new_var(infcx.tcx, universal_regions.fr_fn_body);
     let mut constraints = MirTypeckRegionConstraints {
@@ -153,6 +152,7 @@ pub(crate) fn type_check<'a, 'tcx>(
     };
 
     let mut typeck = TypeChecker {
+        root_cx,
         infcx,
         last_span: body.span,
         body,
@@ -167,7 +167,6 @@ pub(crate) fn type_check<'a, 'tcx>(
         polonius_facts,
         borrow_set,
         constraints: &mut constraints,
-        concrete_opaque_types,
         polonius_liveness,
     };
 
@@ -215,6 +214,7 @@ enum FieldAccessError {
 /// way, it accrues region constraints -- these can later be used by
 /// NLL region checking.
 struct TypeChecker<'a, 'tcx> {
+    root_cx: &'a mut BorrowCheckRootCtxt<'tcx>,
     infcx: &'a BorrowckInferCtxt<'tcx>,
     last_span: Span,
     body: &'a Body<'tcx>,
@@ -233,7 +233,6 @@ struct TypeChecker<'a, 'tcx> {
     polonius_facts: &'a mut Option<PoloniusFacts>,
     borrow_set: &'a BorrowSet<'tcx>,
     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
-    concrete_opaque_types: &'a mut ConcreteOpaqueTypes<'tcx>,
     /// When using `-Zpolonius=next`, the liveness helper data used to create polonius constraints.
     polonius_liveness: Option<PoloniusLivenessContext>,
 }
@@ -2503,11 +2502,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         args: GenericArgsRef<'tcx>,
         locations: Locations,
     ) -> ty::InstantiatedPredicates<'tcx> {
-        let closure_borrowck_results = tcx.mir_borrowck(def_id);
-        self.concrete_opaque_types
-            .extend_from_nested_body(tcx, &closure_borrowck_results.concrete_opaque_types);
-
-        if let Some(closure_requirements) = &closure_borrowck_results.closure_requirements {
+        if let Some(closure_requirements) = &self.root_cx.closure_requirements(def_id) {
             constraint_conversion::ConstraintConversion::new(
                 self.infcx,
                 self.universal_regions,