Auto merge of #99806 - oli-obk:unconstrained_opaque_type, r=estebank

Allow patterns to constrain the hidden type of opaque types

fixes #96572

reverts a revert as original PR was a perf regression that was fixed by reverting it: https://github.com/rust-lang/rust/pull/99368#issuecomment-1186587864)

TODO:

* check if https://github.com/rust-lang/rust/issues/99685 is avoided

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2146,7 +2146,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             }
                             StorageDeadOrDrop::Destructor(_) => kind,
                         },
-                        ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
+                        ProjectionElem::OpaqueCast { .. }
+                        | ProjectionElem::Field(..)
+                        | ProjectionElem::Downcast(..) => {
                             match place_ty.ty.kind() {
                                 ty::Adt(def, _) if def.has_dtor(tcx) => {
                                     // Report the outermost adt with a destructor

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -237,6 +237,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
                 ProjectionElem::Downcast(..) if opt.including_downcast => return None,
                 ProjectionElem::Downcast(..) => (),
+                ProjectionElem::OpaqueCast(..) => (),
                 ProjectionElem::Field(field, _ty) => {
                     // FIXME(project-rfc_2229#36): print capture precisely here.
                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
@@ -317,6 +318,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     PlaceRef { local, projection: proj_base }.ty(self.body, self.infcx.tcx)
                 }
                 ProjectionElem::Downcast(..) => place.ty(self.body, self.infcx.tcx),
+                ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(*ty),
                 ProjectionElem::Field(_, field_type) => PlaceTy::from_ty(*field_type),
             },
         };

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -169,6 +169,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         ..,
                         ProjectionElem::Index(_)
                         | ProjectionElem::ConstantIndex { .. }
+                        | ProjectionElem::OpaqueCast { .. }
                         | ProjectionElem::Subslice { .. }
                         | ProjectionElem::Downcast(..),
                     ],

compiler/rustc_borrowck/src/lib.rs

@@ -1781,6 +1781,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         for (place_base, elem) in place.iter_projections().rev() {
             match elem {
                 ProjectionElem::Index(_/*operand*/) |
+                ProjectionElem::OpaqueCast(_) |
                 ProjectionElem::ConstantIndex { .. } |
                 // assigning to P[i] requires P to be valid.
                 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
@@ -2172,6 +2173,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     | ProjectionElem::Index(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. }
+                    | ProjectionElem::OpaqueCast { .. }
                     | ProjectionElem::Downcast(..) => {
                         let upvar_field_projection = self.is_upvar_field_projection(place);
                         if let Some(field) = upvar_field_projection {

compiler/rustc_borrowck/src/places_conflict.rs

@@ -250,6 +250,7 @@ fn place_components_conflict<'tcx>(
                 | (ProjectionElem::Index { .. }, _, _)
                 | (ProjectionElem::ConstantIndex { .. }, _, _)
                 | (ProjectionElem::Subslice { .. }, _, _)
+                | (ProjectionElem::OpaqueCast { .. }, _, _)
                 | (ProjectionElem::Downcast { .. }, _, _) => {
                     // Recursive case. This can still be disjoint on a
                     // further iteration if this a shallow access and
@@ -317,6 +318,17 @@ fn place_projection_conflict<'tcx>(
             debug!("place_element_conflict: DISJOINT-OR-EQ-DEREF");
             Overlap::EqualOrDisjoint
         }
+        (ProjectionElem::OpaqueCast(v1), ProjectionElem::OpaqueCast(v2)) => {
+            if v1 == v2 {
+                // same type - recur.
+                debug!("place_element_conflict: DISJOINT-OR-EQ-OPAQUE");
+                Overlap::EqualOrDisjoint
+            } else {
+                // Different types. Disjoint!
+                debug!("place_element_conflict: DISJOINT-OPAQUE");
+                Overlap::Disjoint
+            }
+        }
         (ProjectionElem::Field(f1, _), ProjectionElem::Field(f2, _)) => {
             if f1 == f2 {
                 // same field (e.g., `a.y` vs. `a.y`) - recur.
@@ -520,6 +532,7 @@ fn place_projection_conflict<'tcx>(
             | ProjectionElem::Field(..)
             | ProjectionElem::Index(..)
             | ProjectionElem::ConstantIndex { .. }
+            | ProjectionElem::OpaqueCast { .. }
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Downcast(..),
             _,

compiler/rustc_borrowck/src/prefixes.rs

@@ -81,6 +81,7 @@ impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {
                         }
                         ProjectionElem::Downcast(..)
                         | ProjectionElem::Subslice { .. }
+                        | ProjectionElem::OpaqueCast { .. }
                         | ProjectionElem::ConstantIndex { .. }
                         | ProjectionElem::Index(_) => {
                             cursor = cursor_base;

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -764,6 +764,19 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 }
                 PlaceTy::from_ty(fty)
             }
+            ProjectionElem::OpaqueCast(ty) => {
+                let ty = self.sanitize_type(place, ty);
+                let ty = self.cx.normalize(ty, location);
+                self.cx
+                    .eq_types(
+                        base.ty,
+                        ty,
+                        location.to_locations(),
+                        ConstraintCategory::TypeAnnotation,
+                    )
+                    .unwrap();
+                PlaceTy::from_ty(ty)
+            }
         }
     }
 
@@ -1170,10 +1183,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 tcx,
                 self.param_env,
                 proj,
-                |this, field, ()| {
+                |this, field, _| {
                     let ty = this.field_ty(tcx, field);
                     self.normalize(ty, locations)
                 },
+                |_, _| unreachable!(),
             );
             curr_projected_ty = projected_ty;
         }
@@ -2503,6 +2517,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
                 ProjectionElem::Field(..)
                 | ProjectionElem::Downcast(..)
+                | ProjectionElem::OpaqueCast(..)
                 | ProjectionElem::Index(..)
                 | ProjectionElem::ConstantIndex { .. }
                 | ProjectionElem::Subslice { .. } => {

compiler/rustc_codegen_cranelift/src/base.rs

@@ -850,6 +850,7 @@ pub(crate) fn codegen_place<'tcx>(
             PlaceElem::Deref => {
                 cplace = cplace.place_deref(fx);
             }
+            PlaceElem::OpaqueCast(ty) => cplace = cplace.place_opaque_cast(fx, ty),
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }

compiler/rustc_codegen_cranelift/src/value_and_place.rs

@@ -621,6 +621,14 @@ impl<'tcx> CPlace<'tcx> {
         }
     }
 
+    pub(crate) fn place_opaque_cast(
+        self,
+        fx: &mut FunctionCx<'_, '_, 'tcx>,
+        ty: Ty<'tcx>,
+    ) -> CPlace<'tcx> {
+        CPlace { inner: self.inner, layout: fx.layout_of(ty) }
+    }
+
     pub(crate) fn place_field(
         self,
         fx: &mut FunctionCx<'_, '_, 'tcx>,

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -400,6 +400,21 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
         downcast
     }
 
+    pub fn project_type<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
+        &self,
+        bx: &mut Bx,
+        ty: Ty<'tcx>,
+    ) -> Self {
+        let mut downcast = *self;
+        downcast.layout = bx.cx().layout_of(ty);
+
+        // Cast to the appropriate type.
+        let variant_ty = bx.cx().backend_type(downcast.layout);
+        downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
+
+        downcast
+    }
+
     pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
         bx.lifetime_start(self.llval, self.layout.size);
     }
@@ -442,6 +457,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 mir::ProjectionElem::Field(ref field, _) => {
                     cg_base.project_field(bx, field.index())
                 }
+                mir::ProjectionElem::OpaqueCast(ty) => cg_base.project_type(bx, ty),
                 mir::ProjectionElem::Index(index) => {
                     let index = &mir::Operand::Copy(mir::Place::from(index));
                     let index = self.codegen_operand(bx, index);

compiler/rustc_const_eval/src/interpret/projection.rs

@@ -350,6 +350,11 @@ where
     ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> {
         use rustc_middle::mir::ProjectionElem::*;
         Ok(match proj_elem {
+            OpaqueCast(ty) => {
+                let mut place = base.clone();
+                place.layout = self.layout_of(ty)?;
+                place
+            }
             Field(field, _) => self.place_field(base, field.index())?,
             Downcast(_, variant) => self.place_downcast(base, variant)?,
             Deref => self.deref_operand(&self.place_to_op(base)?)?.into(),
@@ -374,6 +379,11 @@ where
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
         use rustc_middle::mir::ProjectionElem::*;
         Ok(match proj_elem {
+            OpaqueCast(ty) => {
+                let mut op = base.clone();
+                op.layout = self.layout_of(ty)?;
+                op
+            }
             Field(field, _) => self.operand_field(base, field.index())?,
             Downcast(_, variant) => self.operand_downcast(base, variant)?,
             Deref => self.deref_operand(base)?.into(),

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -656,6 +656,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
             ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Downcast(..)
+            | ProjectionElem::OpaqueCast(..)
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Field(..)
             | ProjectionElem::Index(_) => {}

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -308,6 +308,7 @@ where
 
             ProjectionElem::Deref
             | ProjectionElem::Field(_, _)
+            | ProjectionElem::OpaqueCast(_)
             | ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Downcast(_, _)

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -361,7 +361,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                             return Err(Unpromotable);
                         }
                     }
-                    ProjectionElem::Downcast(..) => {
+                    ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
                         return Err(Unpromotable);
                     }
 

compiler/rustc_middle/src/mir/mod.rs

@@ -1380,6 +1380,7 @@ impl<V, T> ProjectionElem<V, T> {
 
             Self::Field(_, _)
             | Self::Index(_)
+            | Self::OpaqueCast(_)
             | Self::ConstantIndex { .. }
             | Self::Subslice { .. }
             | Self::Downcast(_, _) => false,
@@ -1574,7 +1575,9 @@ impl Debug for Place<'_> {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
         for elem in self.projection.iter().rev() {
             match elem {
-                ProjectionElem::Downcast(_, _) | ProjectionElem::Field(_, _) => {
+                ProjectionElem::OpaqueCast(_)
+                | ProjectionElem::Downcast(_, _)
+                | ProjectionElem::Field(_, _) => {
                     write!(fmt, "(").unwrap();
                 }
                 ProjectionElem::Deref => {
@@ -1590,6 +1593,9 @@ impl Debug for Place<'_> {
 
         for elem in self.projection.iter() {
             match elem {
+                ProjectionElem::OpaqueCast(ty) => {
+                    write!(fmt, " as {})", ty)?;
+                }
                 ProjectionElem::Downcast(Some(name), _index) => {
                     write!(fmt, " as {})", name)?;
                 }

compiler/rustc_middle/src/mir/syntax.rs

@@ -829,6 +829,9 @@ pub type AssertMessage<'tcx> = AssertKind<Operand<'tcx>>;
 ///    generator has more than one variant, the parent place's variant index must be set, indicating
 ///    which variant is being used. If it has just one variant, the variant index may or may not be
 ///    included - the single possible variant is inferred if it is not included.
+///  - [`OpaqueCast`](ProjectionElem::OpaqueCast): This projection changes the place's type to the
+///    given one, and makes no other changes. A `OpaqueCast` projection on any type other than an
+///    opaque type from the current crate is not well-formed.
 ///  - [`ConstantIndex`](ProjectionElem::ConstantIndex): Computes an offset in units of `T` into the
 ///    place as described in the documentation for the `ProjectionElem`. The resulting address is
 ///    the parent's address plus that offset, and the type is `T`. This is only legal if the parent
@@ -928,6 +931,10 @@ pub enum ProjectionElem<V, T> {
     ///
     /// The included Symbol is the name of the variant, used for printing MIR.
     Downcast(Option<Symbol>, VariantIdx),
+
+    /// Like an explicit cast from an opaque type to a concrete type, but without
+    /// requiring an intermediate variable.
+    OpaqueCast(T),
 }
 
 /// Alias for projections as they appear in places, where the base is a place

compiler/rustc_middle/src/mir/tcx.rs

@@ -56,7 +56,7 @@ impl<'tcx> PlaceTy<'tcx> {
     /// `PlaceElem`, where we can just use the `Ty` that is already
     /// stored inline on field projection elems.
     pub fn projection_ty(self, tcx: TyCtxt<'tcx>, elem: PlaceElem<'tcx>) -> PlaceTy<'tcx> {
-        self.projection_ty_core(tcx, ty::ParamEnv::empty(), &elem, |_, _, ty| ty)
+        self.projection_ty_core(tcx, ty::ParamEnv::empty(), &elem, |_, _, ty| ty, |_, ty| ty)
     }
 
     /// `place_ty.projection_ty_core(tcx, elem, |...| { ... })`
@@ -70,6 +70,7 @@ impl<'tcx> PlaceTy<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         elem: &ProjectionElem<V, T>,
         mut handle_field: impl FnMut(&Self, Field, T) -> Ty<'tcx>,
+        mut handle_opaque_cast: impl FnMut(&Self, T) -> Ty<'tcx>,
     ) -> PlaceTy<'tcx>
     where
         V: ::std::fmt::Debug,
@@ -108,6 +109,7 @@ impl<'tcx> PlaceTy<'tcx> {
                 PlaceTy { ty: self.ty, variant_index: Some(index) }
             }
             ProjectionElem::Field(f, fty) => PlaceTy::from_ty(handle_field(&self, f, fty)),
+            ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(handle_opaque_cast(&self, ty)),
         };
         debug!("projection_ty self: {:?} elem: {:?} yields: {:?}", self, elem, answer);
         answer

compiler/rustc_middle/src/mir/visit.rs

@@ -1084,6 +1084,11 @@ macro_rules! visit_place_fns {
                     self.visit_ty(&mut new_ty, TyContext::Location(location));
                     if ty != new_ty { Some(PlaceElem::Field(field, new_ty)) } else { None }
                 }
+                PlaceElem::OpaqueCast(ty) => {
+                    let mut new_ty = ty;
+                    self.visit_ty(&mut new_ty, TyContext::Location(location));
+                    if ty != new_ty { Some(PlaceElem::OpaqueCast(new_ty)) } else { None }
+                }
                 PlaceElem::Deref
                 | PlaceElem::ConstantIndex { .. }
                 | PlaceElem::Subslice { .. }
@@ -1153,7 +1158,7 @@ macro_rules! visit_place_fns {
             location: Location,
         ) {
             match elem {
-                ProjectionElem::Field(_field, ty) => {
+                ProjectionElem::OpaqueCast(ty) | ProjectionElem::Field(_, ty) => {
                     self.visit_ty(ty, TyContext::Location(location));
                 }
                 ProjectionElem::Index(local) => {

compiler/rustc_mir_build/src/build/expr/as_place.rs

@@ -69,7 +69,7 @@ pub(crate) enum PlaceBase {
 /// This is used internally when building a place for an expression like `a.b.c`. The fields `b`
 /// and `c` can be progressively pushed onto the place builder that is created when converting `a`.
 #[derive(Clone, Debug, PartialEq)]
-pub(crate) struct PlaceBuilder<'tcx> {
+pub(in crate::build) struct PlaceBuilder<'tcx> {
     base: PlaceBase,
     projection: Vec<PlaceElem<'tcx>>,
 }
@@ -102,6 +102,8 @@ fn convert_to_hir_projections_and_truncate_for_capture<'tcx>(
                 variant = Some(*idx);
                 continue;
             }
+            // These do not affect anything, they just make sure we know the right type.
+            ProjectionElem::OpaqueCast(_) => continue,
             ProjectionElem::Index(..)
             | ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Subslice { .. } => {
@@ -168,22 +170,22 @@ fn find_capture_matching_projections<'a, 'tcx>(
 /// `PlaceBuilder` now starts from `PlaceBase::Local`.
 ///
 /// Returns a Result with the error being the PlaceBuilder (`from_builder`) that was not found.
-fn to_upvars_resolved_place_builder<'a, 'tcx>(
+#[instrument(level = "trace", skip(cx), ret)]
+fn to_upvars_resolved_place_builder<'tcx>(
     from_builder: PlaceBuilder<'tcx>,
-    tcx: TyCtxt<'tcx>,
+    cx: &Builder<'_, 'tcx>,
-    upvars: &'a CaptureMap<'tcx>,
 ) -> Result<PlaceBuilder<'tcx>, PlaceBuilder<'tcx>> {
     match from_builder.base {
         PlaceBase::Local(_) => Ok(from_builder),
         PlaceBase::Upvar { var_hir_id, closure_def_id } => {
             let Some((capture_index, capture)) =
                 find_capture_matching_projections(
-                    upvars,
+                    &cx.upvars,
                     var_hir_id,
                     &from_builder.projection,
                 ) else {
-                let closure_span = tcx.def_span(closure_def_id);
+                let closure_span = cx.tcx.def_span(closure_def_id);
-                if !enable_precise_capture(tcx, closure_span) {
+                if !enable_precise_capture(cx.tcx, closure_span) {
                     bug!(
                         "No associated capture found for {:?}[{:#?}] even though \
                             capture_disjoint_fields isn't enabled",
@@ -200,12 +202,13 @@ fn to_upvars_resolved_place_builder<'a, 'tcx>(
             };
 
             // Access the capture by accessing the field within the Closure struct.
-            let capture_info = &upvars[capture_index];
+            let capture_info = &cx.upvars[capture_index];
 
             let mut upvar_resolved_place_builder = PlaceBuilder::from(capture_info.use_place);
 
             // We used some of the projections to build the capture itself,
             // now we apply the remaining to the upvar resolved place.
+            trace!(?capture.captured_place, ?from_builder.projection);
             let remaining_projections = strip_prefix(
                 capture.captured_place.place.base_ty,
                 from_builder.projection,
@@ -230,16 +233,21 @@ fn strip_prefix<'tcx>(
     prefix_projections: &[HirProjection<'tcx>],
 ) -> impl Iterator<Item = PlaceElem<'tcx>> {
     let mut iter = projections.into_iter();
+    let mut next = || match iter.next()? {
+        // Filter out opaque casts, they are unnecessary in the prefix.
+        ProjectionElem::OpaqueCast(..) => iter.next(),
+        other => Some(other),
+    };
     for projection in prefix_projections {
         match projection.kind {
             HirProjectionKind::Deref => {
-                assert!(matches!(iter.next(), Some(ProjectionElem::Deref)));
+                assert!(matches!(next(), Some(ProjectionElem::Deref)));
             }
             HirProjectionKind::Field(..) => {
                 if base_ty.is_enum() {
-                    assert!(matches!(iter.next(), Some(ProjectionElem::Downcast(..))));
+                    assert!(matches!(next(), Some(ProjectionElem::Downcast(..))));
                 }
-                assert!(matches!(iter.next(), Some(ProjectionElem::Field(..))));
+                assert!(matches!(next(), Some(ProjectionElem::Field(..))));
             }
             HirProjectionKind::Index | HirProjectionKind::Subslice => {
                 bug!("unexpected projection kind: {:?}", projection);
@@ -251,24 +259,16 @@ fn strip_prefix<'tcx>(
 }
 
 impl<'tcx> PlaceBuilder<'tcx> {
-    pub(in crate::build) fn into_place<'a>(
+    pub(in crate::build) fn into_place(self, cx: &Builder<'_, 'tcx>) -> Place<'tcx> {
-        self,
-        tcx: TyCtxt<'tcx>,
-        upvars: &'a CaptureMap<'tcx>,
-    ) -> Place<'tcx> {
         if let PlaceBase::Local(local) = self.base {
-            Place { local, projection: tcx.intern_place_elems(&self.projection) }
+            Place { local, projection: cx.tcx.intern_place_elems(&self.projection) }
         } else {
-            self.expect_upvars_resolved(tcx, upvars).into_place(tcx, upvars)
+            self.expect_upvars_resolved(cx).into_place(cx)
         }
     }
 
-    fn expect_upvars_resolved<'a>(
+    fn expect_upvars_resolved(self, cx: &Builder<'_, 'tcx>) -> PlaceBuilder<'tcx> {
-        self,
+        to_upvars_resolved_place_builder(self, cx).unwrap()
-        tcx: TyCtxt<'tcx>,
-        upvars: &'a CaptureMap<'tcx>,
-    ) -> PlaceBuilder<'tcx> {
-        to_upvars_resolved_place_builder(self, tcx, upvars).unwrap()
     }
 
     /// Attempts to resolve the `PlaceBuilder`.
@@ -282,18 +282,21 @@ impl<'tcx> PlaceBuilder<'tcx> {
     /// not captured. This can happen because the final mir that will be
     /// generated doesn't require a read for this place. Failures will only
     /// happen inside closures.
-    pub(in crate::build) fn try_upvars_resolved<'a>(
+    pub(in crate::build) fn try_upvars_resolved(
         self,
-        tcx: TyCtxt<'tcx>,
+        cx: &Builder<'_, 'tcx>,
-        upvars: &'a CaptureMap<'tcx>,
     ) -> Result<PlaceBuilder<'tcx>, PlaceBuilder<'tcx>> {
-        to_upvars_resolved_place_builder(self, tcx, upvars)
+        to_upvars_resolved_place_builder(self, cx)
     }
 
     pub(crate) fn base(&self) -> PlaceBase {
         self.base
     }
 
+    pub(crate) fn projection(&self) -> &[PlaceElem<'tcx>] {
+        &self.projection
+    }
+
     pub(crate) fn field(self, f: Field, ty: Ty<'tcx>) -> Self {
         self.project(PlaceElem::Field(f, ty))
     }
@@ -353,7 +356,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         expr: &Expr<'tcx>,
     ) -> BlockAnd<Place<'tcx>> {
         let place_builder = unpack!(block = self.as_place_builder(block, expr));
-        block.and(place_builder.into_place(self.tcx, &self.upvars))
+        block.and(place_builder.into_place(self))
     }
 
     /// This is used when constructing a compound `Place`, so that we can avoid creating
@@ -377,7 +380,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         expr: &Expr<'tcx>,
     ) -> BlockAnd<Place<'tcx>> {
         let place_builder = unpack!(block = self.as_read_only_place_builder(block, expr));
-        block.and(place_builder.into_place(self.tcx, &self.upvars))
+        block.and(place_builder.into_place(self))
     }
 
     /// This is used when constructing a compound `Place`, so that we can avoid creating
@@ -472,7 +475,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             inferred_ty: expr.ty,
                         });
 
-                    let place = place_builder.clone().into_place(this.tcx, &this.upvars);
+                    let place = place_builder.clone().into_place(this);
                     this.cfg.push(
                         block,
                         Statement {
@@ -610,7 +613,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         if is_outermost_index {
             self.read_fake_borrows(block, fake_borrow_temps, source_info)
         } else {
-            base_place = base_place.expect_upvars_resolved(self.tcx, &self.upvars);
+            base_place = base_place.expect_upvars_resolved(self);
             self.add_fake_borrows_of_base(
                 &base_place,
                 block,
@@ -638,12 +641,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let lt = self.temp(bool_ty, expr_span);
 
         // len = len(slice)
-        self.cfg.push_assign(
+        self.cfg.push_assign(block, source_info, len, Rvalue::Len(slice.into_place(self)));
-            block,
-            source_info,
-            len,
-            Rvalue::Len(slice.into_place(self.tcx, &self.upvars)),
-        );
         // lt = idx < len
         self.cfg.push_assign(
             block,
@@ -723,6 +721,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     }
                     ProjectionElem::Field(..)
                     | ProjectionElem::Downcast(..)
+                    | ProjectionElem::OpaqueCast(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. } => (),
                 }

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -329,10 +329,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     let place_builder =
                         unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
 
-                    if let Ok(place_builder_resolved) =
+                    if let Ok(place_builder_resolved) = place_builder.try_upvars_resolved(this) {
-                        place_builder.try_upvars_resolved(this.tcx, &this.upvars)
+                        let mir_place = place_builder_resolved.into_place(this);
-                    {
-                        let mir_place = place_builder_resolved.into_place(this.tcx, &this.upvars);
                         this.cfg.push_fake_read(
                             block,
                             this.source_info(this.tcx.hir().span(*hir_id)),
@@ -623,8 +621,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // by the parent itself. The mutability of the current capture
             // is same as that of the capture in the parent closure.
             PlaceBase::Upvar { .. } => {
-                let enclosing_upvars_resolved =
+                let enclosing_upvars_resolved = arg_place_builder.clone().into_place(this);
-                    arg_place_builder.clone().into_place(this.tcx, &this.upvars);
 
                 match enclosing_upvars_resolved.as_ref() {
                     PlaceRef {
@@ -661,7 +658,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
         };
 
-        let arg_place = arg_place_builder.into_place(this.tcx, &this.upvars);
+        let arg_place = arg_place_builder.into_place(this);
 
         this.cfg.push_assign(
             block,

compiler/rustc_mir_build/src/build/expr/as_temp.rs

@@ -23,6 +23,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         ensure_sufficient_stack(|| self.as_temp_inner(block, temp_lifetime, expr, mutability))
     }
 
+    #[instrument(skip(self), level = "debug")]
     fn as_temp_inner(
         &mut self,
         mut block: BasicBlock,
@@ -30,10 +31,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         expr: &Expr<'tcx>,
         mutability: Mutability,
     ) -> BlockAnd<Local> {
-        debug!(
-            "as_temp(block={:?}, temp_lifetime={:?}, expr={:?}, mutability={:?})",
-            block, temp_lifetime, expr, mutability
-        );
         let this = self;
 
         let expr_span = expr.span;

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -15,14 +15,13 @@ use std::iter;
 impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// Compile `expr`, storing the result into `destination`, which
     /// is assumed to be uninitialized.
+    #[instrument(level = "debug", skip(self))]
     pub(crate) fn expr_into_dest(
         &mut self,
         destination: Place<'tcx>,
         mut block: BasicBlock,
         expr: &Expr<'tcx>,
     ) -> BlockAnd<()> {
-        debug!("expr_into_dest(destination={:?}, block={:?}, expr={:?})", destination, block, expr);
-
         // since we frequently have to reference `self` from within a
         // closure, where `self` would be shadowed, it's easier to
         // just use the name `this` uniformly
@@ -366,7 +365,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             None => {
                                 let place_builder = place_builder.clone();
                                 this.consume_by_copy_or_move(
-                                    place_builder.field(n, *ty).into_place(this.tcx, &this.upvars),
+                                    place_builder.field(n, *ty).into_place(this),
                                 )
                             }
                         })

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -220,10 +220,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let cause_matched_place = FakeReadCause::ForMatchedPlace(None);
         let source_info = self.source_info(scrutinee_span);
 
-        if let Ok(scrutinee_builder) =
+        if let Ok(scrutinee_builder) = scrutinee_place_builder.clone().try_upvars_resolved(self) {
-            scrutinee_place_builder.clone().try_upvars_resolved(self.tcx, &self.upvars)
+            let scrutinee_place = scrutinee_builder.into_place(self);
-        {
-            let scrutinee_place = scrutinee_builder.into_place(self.tcx, &self.upvars);
             self.cfg.push_fake_read(block, source_info, cause_matched_place, scrutinee_place);
         }
 
@@ -246,7 +244,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             .map(|arm| {
                 let arm = &self.thir[arm];
                 let arm_has_guard = arm.guard.is_some();
-                let arm_candidate = Candidate::new(scrutinee.clone(), &arm.pattern, arm_has_guard);
+                let arm_candidate =
+                    Candidate::new(scrutinee.clone(), &arm.pattern, arm_has_guard, self);
                 (arm, arm_candidate)
             })
             .collect()
@@ -349,9 +348,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     let mut opt_scrutinee_place: Option<(Option<&Place<'tcx>>, Span)> = None;
                     let scrutinee_place: Place<'tcx>;
                     if let Ok(scrutinee_builder) =
-                        scrutinee_place_builder.clone().try_upvars_resolved(this.tcx, &this.upvars)
+                        scrutinee_place_builder.clone().try_upvars_resolved(this)
                     {
-                        scrutinee_place = scrutinee_builder.into_place(this.tcx, &this.upvars);
+                        scrutinee_place = scrutinee_builder.into_place(this);
                         opt_scrutinee_place = Some((Some(&scrutinee_place), scrutinee_span));
                     }
                     let scope = this.declare_bindings(
@@ -584,7 +583,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         initializer: PlaceBuilder<'tcx>,
         set_match_place: bool,
     ) -> BlockAnd<()> {
-        let mut candidate = Candidate::new(initializer.clone(), &irrefutable_pat, false);
+        let mut candidate = Candidate::new(initializer.clone(), &irrefutable_pat, false, self);
         let fake_borrow_temps = self.lower_match_tree(
             block,
             irrefutable_pat.span,
@@ -601,12 +600,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             while let Some(next) = {
                 for binding in &candidate_ref.bindings {
                     let local = self.var_local_id(binding.var_id, OutsideGuard);
-
-                    let Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
-                        VarBindingForm { opt_match_place: Some((ref mut match_place, _)), .. },
-                    )))) = self.local_decls[local].local_info else {
-                        bug!("Let binding to non-user variable.")
-                    };
                     // `try_upvars_resolved` may fail if it is unable to resolve the given
                     // `PlaceBuilder` inside a closure. In this case, we don't want to include
                     // a scrutinee place. `scrutinee_place_builder` will fail for destructured
@@ -621,10 +614,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     //    let (v1, v2) = foo;
                     // };
                     // ```
-                    if let Ok(match_pair_resolved) =
+                    if let Ok(match_pair_resolved) = initializer.clone().try_upvars_resolved(self) {
-                        initializer.clone().try_upvars_resolved(self.tcx, &self.upvars)
+                        let place = match_pair_resolved.into_place(self);
-                    {
+
-                        let place = match_pair_resolved.into_place(self.tcx, &self.upvars);
+                        let Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
+                            VarBindingForm { opt_match_place: Some((ref mut match_place, _)), .. },
+                        )))) = self.local_decls[local].local_info else {
+                            bug!("Let binding to non-user variable.")
+                        };
                         *match_place = Some(place);
                     }
                 }
@@ -654,6 +651,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// scope for the bindings in these patterns, if such a scope had to be
     /// created. NOTE: Declaring the bindings should always be done in their
     /// drop scope.
+    #[instrument(skip(self), level = "debug")]
     pub(crate) fn declare_bindings(
         &mut self,
         mut visibility_scope: Option<SourceScope>,
@@ -662,7 +660,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         has_guard: ArmHasGuard,
         opt_match_place: Option<(Option<&Place<'tcx>>, Span)>,
     ) -> Option<SourceScope> {
-        debug!("declare_bindings: pattern={:?}", pattern);
         self.visit_primary_bindings(
             &pattern,
             UserTypeProjections::none(),
@@ -868,11 +865,16 @@ struct Candidate<'pat, 'tcx> {
 }
 
 impl<'tcx, 'pat> Candidate<'pat, 'tcx> {
-    fn new(place: PlaceBuilder<'tcx>, pattern: &'pat Pat<'tcx>, has_guard: bool) -> Self {
+    fn new(
+        place: PlaceBuilder<'tcx>,
+        pattern: &'pat Pat<'tcx>,
+        has_guard: bool,
+        cx: &Builder<'_, 'tcx>,
+    ) -> Self {
         Candidate {
             span: pattern.span,
             has_guard,
-            match_pairs: smallvec![MatchPair { place, pattern }],
+            match_pairs: smallvec![MatchPair::new(place, pattern, cx)],
             bindings: Vec::new(),
             ascriptions: Vec::new(),
             subcandidates: Vec::new(),
@@ -1048,6 +1050,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// if `x.0` matches `false` (for the third arm). In the (impossible at
     /// runtime) case when `x.0` is now `true`, we branch to
     /// `otherwise_block`.
+    #[instrument(skip(self, fake_borrows), level = "debug")]
     fn match_candidates<'pat>(
         &mut self,
         span: Span,
@@ -1057,11 +1060,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         candidates: &mut [&mut Candidate<'pat, 'tcx>],
         fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
     ) {
-        debug!(
-            "matched_candidate(span={:?}, candidates={:?}, start_block={:?}, otherwise_block={:?})",
-            span, candidates, start_block, otherwise_block,
-        );
-
         // Start by simplifying candidates. Once this process is complete, all
         // the match pairs which remain require some form of test, whether it
         // be a switch or pattern comparison.
@@ -1380,6 +1378,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         )
     }
 
+    #[instrument(
+        skip(self, otherwise, or_span, place, fake_borrows, candidate, pats),
+        level = "debug"
+    )]
     fn test_or_pattern<'pat>(
         &mut self,
         candidate: &mut Candidate<'pat, 'tcx>,
@@ -1389,10 +1391,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         place: PlaceBuilder<'tcx>,
         fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
     ) {
-        debug!("test_or_pattern:\ncandidate={:#?}\npats={:#?}", candidate, pats);
+        debug!("candidate={:#?}\npats={:#?}", candidate, pats);
         let mut or_candidates: Vec<_> = pats
             .iter()
-            .map(|pat| Candidate::new(place.clone(), pat, candidate.has_guard))
+            .map(|pat| Candidate::new(place.clone(), pat, candidate.has_guard, self))
             .collect();
         let mut or_candidate_refs: Vec<_> = or_candidates.iter_mut().collect();
         let otherwise = if candidate.otherwise_block.is_some() {
@@ -1605,9 +1607,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         // Insert a Shallow borrow of any places that is switched on.
         if let Some(fb) = fake_borrows && let Ok(match_place_resolved) =
-            match_place.clone().try_upvars_resolved(self.tcx, &self.upvars)
+            match_place.clone().try_upvars_resolved(self)
         {
-            let resolved_place = match_place_resolved.into_place(self.tcx, &self.upvars);
+            let resolved_place = match_place_resolved.into_place(self);
             fb.insert(resolved_place);
         }
 
@@ -1634,9 +1636,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             candidates = rest;
         }
         // at least the first candidate ought to be tested
-        assert!(total_candidate_count > candidates.len());
+        assert!(
-        debug!("test_candidates: tested_candidates: {}", total_candidate_count - candidates.len());
+            total_candidate_count > candidates.len(),
-        debug!("test_candidates: untested_candidates: {}", candidates.len());
+            "{}, {:#?}",
+            total_candidate_count,
+            candidates
+        );
+        debug!("tested_candidates: {}", total_candidate_count - candidates.len());
+        debug!("untested_candidates: {}", candidates.len());
 
         // HACK(matthewjasper) This is a closure so that we can let the test
         // create its blocks before the rest of the match. This currently
@@ -1783,8 +1790,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let expr_span = expr.span;
         let expr_place_builder = unpack!(block = self.lower_scrutinee(block, expr, expr_span));
         let wildcard = Pat::wildcard_from_ty(pat.ty);
-        let mut guard_candidate = Candidate::new(expr_place_builder.clone(), &pat, false);
+        let mut guard_candidate = Candidate::new(expr_place_builder.clone(), &pat, false, self);
-        let mut otherwise_candidate = Candidate::new(expr_place_builder.clone(), &wildcard, false);
+        let mut otherwise_candidate =
+            Candidate::new(expr_place_builder.clone(), &wildcard, false, self);
         let fake_borrow_temps = self.lower_match_tree(
             block,
             pat.span,
@@ -1794,8 +1802,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         );
         let mut opt_expr_place: Option<(Option<&Place<'tcx>>, Span)> = None;
         let expr_place: Place<'tcx>;
-        if let Ok(expr_builder) = expr_place_builder.try_upvars_resolved(self.tcx, &self.upvars) {
+        if let Ok(expr_builder) = expr_place_builder.try_upvars_resolved(self) {
-            expr_place = expr_builder.into_place(self.tcx, &self.upvars);
+            expr_place = expr_builder.into_place(self);
             opt_expr_place = Some((Some(&expr_place), expr_span));
         }
         let otherwise_post_guard_block = otherwise_candidate.pre_binding_block.unwrap();
@@ -2209,6 +2217,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// first local is a binding for occurrences of `var` in the guard, which
     /// will have type `&T`. The second local is a binding for occurrences of
     /// `var` in the arm body, which will have type `T`.
+    #[instrument(skip(self), level = "debug")]
     fn declare_binding(
         &mut self,
         source_info: SourceInfo,
@@ -2223,19 +2232,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         opt_match_place: Option<(Option<Place<'tcx>>, Span)>,
         pat_span: Span,
     ) {
-        debug!(
-            "declare_binding(var_id={:?}, name={:?}, mode={:?}, var_ty={:?}, \
-             visibility_scope={:?}, source_info={:?})",
-            var_id, name, mode, var_ty, visibility_scope, source_info
-        );
-
         let tcx = self.tcx;
         let debug_source_info = SourceInfo { span: source_info.span, scope: visibility_scope };
         let binding_mode = match mode {
             BindingMode::ByValue => ty::BindingMode::BindByValue(mutability),
             BindingMode::ByRef(_) => ty::BindingMode::BindByReference(mutability),
         };
-        debug!("declare_binding: user_ty={:?}", user_ty);
         let local = LocalDecl::<'tcx> {
             mutability,
             ty: var_ty,
@@ -2285,7 +2287,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         } else {
             LocalsForNode::One(for_arm_body)
         };
-        debug!("declare_binding: vars={:?}", locals);
+        debug!(?locals);
         self.var_indices.insert(var_id, locals);
     }
 
@@ -2302,8 +2304,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let (matching, failure) = self.in_if_then_scope(*let_else_scope, |this| {
             let scrutinee = unpack!(block = this.lower_scrutinee(block, init, initializer_span));
             let pat = Pat { ty: init.ty, span: else_block_span, kind: PatKind::Wild };
-            let mut wildcard = Candidate::new(scrutinee.clone(), &pat, false);
+            let mut wildcard = Candidate::new(scrutinee.clone(), &pat, false, this);
-            let mut candidate = Candidate::new(scrutinee.clone(), pattern, false);
+            let mut candidate = Candidate::new(scrutinee.clone(), pattern, false, this);
             let fake_borrow_temps = this.lower_match_tree(
                 block,
                 initializer_span,

compiler/rustc_mir_build/src/build/matches/simplify.rs

@@ -37,12 +37,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     ///
     /// only generates a single switch. If this happens this method returns
     /// `true`.
+    #[instrument(skip(self, candidate), level = "debug")]
     pub(super) fn simplify_candidate<'pat>(
         &mut self,
         candidate: &mut Candidate<'pat, 'tcx>,
     ) -> bool {
         // repeatedly simplify match pairs until fixed point is reached
-        debug!(?candidate, "simplify_candidate");
+        debug!("{candidate:#?}");
 
         // existing_bindings and new_bindings exists to keep the semantics in order.
         // Reversing the binding order for bindings after `@` changes the binding order in places
@@ -131,7 +132,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     ) -> Vec<Candidate<'pat, 'tcx>> {
         pats.iter()
             .map(|box pat| {
-                let mut candidate = Candidate::new(place.clone(), pat, candidate.has_guard);
+                let mut candidate = Candidate::new(place.clone(), pat, candidate.has_guard, self);
                 self.simplify_candidate(&mut candidate);
                 candidate
             })
@@ -155,17 +156,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 ascription: thir::Ascription { ref annotation, variance },
             } => {
                 // Apply the type ascription to the value at `match_pair.place`, which is the
-                if let Ok(place_resolved) =
+                if let Ok(place_resolved) = match_pair.place.clone().try_upvars_resolved(self) {
-                    match_pair.place.clone().try_upvars_resolved(self.tcx, &self.upvars)
-                {
                     candidate.ascriptions.push(Ascription {
                         annotation: annotation.clone(),
-                        source: place_resolved.into_place(self.tcx, &self.upvars),
+                        source: place_resolved.into_place(self),
                         variance,
                     });
                 }
 
-                candidate.match_pairs.push(MatchPair::new(match_pair.place, subpattern));
+                candidate.match_pairs.push(MatchPair::new(match_pair.place, subpattern, self));
 
                 Ok(())
             }
@@ -184,12 +183,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 ref subpattern,
                 is_primary: _,
             } => {
-                if let Ok(place_resolved) =
+                if let Ok(place_resolved) = match_pair.place.clone().try_upvars_resolved(self) {
-                    match_pair.place.clone().try_upvars_resolved(self.tcx, &self.upvars)
-                {
                     candidate.bindings.push(Binding {
                         span: match_pair.pattern.span,
-                        source: place_resolved.into_place(self.tcx, &self.upvars),
+                        source: place_resolved.into_place(self),
                         var_id: var,
                         binding_mode: mode,
                     });
@@ -197,7 +194,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
                 if let Some(subpattern) = subpattern.as_ref() {
                     // this is the `x @ P` case; have to keep matching against `P` now
-                    candidate.match_pairs.push(MatchPair::new(match_pair.place, subpattern));
+                    candidate.match_pairs.push(MatchPair::new(match_pair.place, subpattern, self));
                 }
 
                 Ok(())
@@ -308,7 +305,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             PatKind::Deref { ref subpattern } => {
                 let place_builder = match_pair.place.deref();
-                candidate.match_pairs.push(MatchPair::new(place_builder, subpattern));
+                candidate.match_pairs.push(MatchPair::new(place_builder, subpattern, self));
                 Ok(())
             }
 

compiler/rustc_mir_build/src/build/matches/test.rs

@@ -144,6 +144,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
     }
 
+    #[instrument(skip(self, make_target_blocks, place_builder), level = "debug")]
     pub(super) fn perform_test(
         &mut self,
         match_start_span: Span,
@@ -153,19 +154,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         test: &Test<'tcx>,
         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
     ) {
-        let place: Place<'tcx>;
+        let place = place_builder.into_place(self);
-        if let Ok(test_place_builder) = place_builder.try_upvars_resolved(self.tcx, &self.upvars) {
+        let place_ty = place.ty(&self.local_decls, self.tcx);
-            place = test_place_builder.into_place(self.tcx, &self.upvars);
+        debug!(?place, ?place_ty,);
-        } else {
-            return;
-        }
-        debug!(
-            "perform_test({:?}, {:?}: {:?}, {:?})",
-            block,
-            place,
-            place.ty(&self.local_decls, self.tcx),
-            test
-        );
 
         let source_info = self.source_info(test.span);
         match test.kind {
@@ -733,14 +724,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
         // we want to create a set of derived match-patterns like
         // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
-        let elem =
+        let downcast_place = match_pair.place.downcast(adt_def, variant_index); // `(x as Variant)`
-            ProjectionElem::Downcast(Some(adt_def.variant(variant_index).name), variant_index);
-        let downcast_place = match_pair.place.project(elem); // `(x as Variant)`
         let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
             // e.g., `(x as Variant).0`
             let place = downcast_place.clone().field(subpattern.field, subpattern.pattern.ty);
             // e.g., `(x as Variant).0 @ P1`
-            MatchPair::new(place, &subpattern.pattern)
+            MatchPair::new(place, &subpattern.pattern, self)
         });
 
         candidate.match_pairs.extend(consequent_match_pairs);

compiler/rustc_mir_build/src/build/matches/util.rs

@@ -1,9 +1,11 @@
+use crate::build::expr::as_place::PlaceBase;
 use crate::build::expr::as_place::PlaceBuilder;
 use crate::build::matches::MatchPair;
 use crate::build::Builder;
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use rustc_middle::ty;
+use rustc_middle::ty::TypeVisitable;
 use smallvec::SmallVec;
 use std::convert::TryInto;
 
@@ -17,7 +19,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             .iter()
             .map(|fieldpat| {
                 let place = place.clone().field(fieldpat.field, fieldpat.pattern.ty);
-                MatchPair::new(place, &fieldpat.pattern)
+                MatchPair::new(place, &fieldpat.pattern, self)
             })
             .collect()
     }
@@ -31,11 +33,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         suffix: &'pat [Box<Pat<'tcx>>],
     ) {
         let tcx = self.tcx;
-        let (min_length, exact_size) = if let Ok(place_resolved) =
+        let (min_length, exact_size) =
-            place.clone().try_upvars_resolved(tcx, &self.upvars)
+            if let Ok(place_resolved) = place.clone().try_upvars_resolved(self) {
-        {
+                match place_resolved.into_place(self).ty(&self.local_decls, tcx).ty.kind() {
-            match place_resolved.into_place(tcx, &self.upvars).ty(&self.local_decls, tcx).ty.kind()
-            {
                     ty::Array(_, length) => (length.eval_usize(tcx, self.param_env), true),
                     _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
                 }
@@ -47,7 +47,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             let elem =
                 ProjectionElem::ConstantIndex { offset: idx as u64, min_length, from_end: false };
             let place = place.clone().project(elem);
-            MatchPair::new(place, subpattern)
+            MatchPair::new(place, subpattern, self)
         }));
 
         if let Some(subslice_pat) = opt_slice {
@@ -57,7 +57,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 to: if exact_size { min_length - suffix_len } else { suffix_len },
                 from_end: !exact_size,
             });
-            match_pairs.push(MatchPair::new(subslice, subslice_pat));
+            match_pairs.push(MatchPair::new(subslice, subslice_pat, self));
         }
 
         match_pairs.extend(suffix.iter().rev().enumerate().map(|(idx, subpattern)| {
@@ -68,7 +68,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 from_end: !exact_size,
             };
             let place = place.clone().project(elem);
-            MatchPair::new(place, subpattern)
+            MatchPair::new(place, subpattern, self)
         }));
     }
 
@@ -96,10 +96,29 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 }
 
 impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
-    pub(crate) fn new(
+    pub(in crate::build) fn new(
         place: PlaceBuilder<'tcx>,
         pattern: &'pat Pat<'tcx>,
+        cx: &Builder<'_, 'tcx>,
     ) -> MatchPair<'pat, 'tcx> {
+        // Force the place type to the pattern's type.
+        // FIXME(oli-obk): can we use this to simplify slice/array pattern hacks?
+        let mut place = match place.try_upvars_resolved(cx) {
+            Ok(val) | Err(val) => val,
+        };
+
+        // Only add the OpaqueCast projection if the given place is an opaque type and the
+        // expected type from the pattern is not.
+        let may_need_cast = match place.base() {
+            PlaceBase::Local(local) => {
+                let ty = Place::ty_from(local, place.projection(), &cx.local_decls, cx.tcx).ty;
+                ty != pattern.ty && ty.has_opaque_types()
+            }
+            _ => true,
+        };
+        if may_need_cast {
+            place = place.project(ProjectionElem::OpaqueCast(pattern.ty));
+        }
         MatchPair { place, pattern }
     }
 }

compiler/rustc_mir_build/src/build/scope.rs

@@ -553,6 +553,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
     /// Convenience wrapper that pushes a scope and then executes `f`
     /// to build its contents, popping the scope afterwards.
+    #[instrument(skip(self, f), level = "debug")]
     pub(crate) fn in_scope<F, R>(
         &mut self,
         region_scope: (region::Scope, SourceInfo),
@@ -562,7 +563,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     where
         F: FnOnce(&mut Builder<'a, 'tcx>) -> BlockAnd<R>,
     {
-        debug!("in_scope(region_scope={:?})", region_scope);
         let source_scope = self.source_scope;
         let tcx = self.tcx;
         if let LintLevel::Explicit(current_hir_id) = lint_level {
@@ -589,7 +589,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let rv = unpack!(block = f(self));
         unpack!(block = self.pop_scope(region_scope, block));
         self.source_scope = source_scope;
-        debug!("in_scope: exiting region_scope={:?} block={:?}", region_scope, block);
+        debug!(?block);
         block.and(rv)
     }
 

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -48,6 +48,8 @@ impl<'tcx> Cx<'tcx> {
             _ => None,
         };
 
+        trace!(?expr.ty);
+
         // Now apply adjustments, if any.
         for adjustment in self.typeck_results.expr_adjustments(hir_expr) {
             trace!(?expr, ?adjustment);
@@ -56,6 +58,8 @@ impl<'tcx> Cx<'tcx> {
                 self.apply_adjustment(hir_expr, expr, adjustment, adjustment_span.unwrap_or(span));
         }
 
+        trace!(?expr.ty, "after adjustments");
+
         // Next, wrap this up in the expr's scope.
         expr = Expr {
             temp_lifetime,

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -200,6 +200,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         }
     }
 
+    #[instrument(skip(self), level = "debug")]
     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat<'tcx>) -> Box<Pat<'tcx>> {
         let mut ty = self.typeck_results.node_type(pat.hir_id);
         let mut span = pat.span;

compiler/rustc_mir_build/src/thir/pattern/usefulness.rs

@@ -842,7 +842,15 @@ fn is_useful<'p, 'tcx>(
             }
         }
     } else {
-        let ty = v.head().ty();
+        let mut ty = v.head().ty();
+
+        // Opaque types can't get destructured/split, but the patterns can
+        // actually hint at hidden types, so we use the patterns' types instead.
+        if let ty::Opaque(..) = ty.kind() {
+            if let Some(row) = rows.first() {
+                ty = row.head().ty();
+            }
+        }
         let is_non_exhaustive = cx.is_foreign_non_exhaustive_enum(ty);
         debug!("v.head: {:?}, v.span: {:?}", v.head(), v.head().span());
         let pcx = &PatCtxt { cx, ty, span: v.head().span(), is_top_level, is_non_exhaustive };

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -893,7 +893,7 @@ where
             }
             ty::Slice(ety) => self.open_drop_for_array(*ety, None),
 
-            _ => bug!("open drop from non-ADT `{:?}`", ty),
+            _ => span_bug!(self.source_info.span, "open drop from non-ADT `{:?}`", ty),
         }
     }
 

compiler/rustc_mir_dataflow/src/move_paths/abs_domain.rs

@@ -48,6 +48,7 @@ impl<'tcx> Lift for PlaceElem<'tcx> {
         match *self {
             ProjectionElem::Deref => ProjectionElem::Deref,
             ProjectionElem::Field(f, ty) => ProjectionElem::Field(f, ty.lift()),
+            ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty.lift()),
             ProjectionElem::Index(ref i) => ProjectionElem::Index(i.lift()),
             ProjectionElem::Subslice { from, to, from_end } => {
                 ProjectionElem::Subslice { from, to, from_end }

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug.rs

@@ -1,8 +1,9 @@
 // compile-flags: --edition=2021
+// check-pass
 #![feature(type_alias_impl_trait)]
 
 fn main() {
-    type T = impl Copy; //~ ERROR unconstrained opaque type
+    type T = impl Copy;
     let foo: T = (1u32, 2u32);
     let (a, b): (u32, u32) = foo;
 }

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug.stderr

@@ -1,10 +0,0 @@
-error: unconstrained opaque type
-  --> $DIR/cross_inference_pattern_bug.rs:5:14
-   |
-LL |     type T = impl Copy;
-   |              ^^^^^^^^^
-   |
-   = note: `T` must be used in combination with a concrete type within the same module
-
-error: aborting due to previous error
-

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug_no_type.rs

@@ -1,13 +1,13 @@
-// known-bug: #96572
 // compile-flags: --edition=2021 --crate-type=lib
 // rustc-env:RUST_BACKTRACE=0
+// check-pass
 
 // tracked in https://github.com/rust-lang/rust/issues/96572
 
 #![feature(type_alias_impl_trait)]
 
 fn main() {
-    type T = impl Copy;  // error: unconstrained opaque type
+    type T = impl Copy;
     let foo: T = (1u32, 2u32);
-    let (a, b) = foo; // removing this line makes the code compile
+    let (a, b) = foo; // this line used to make the code fail
 }

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug_no_type.stderr

@@ -1,10 +0,0 @@
-error: unconstrained opaque type
-  --> $DIR/cross_inference_pattern_bug_no_type.rs:10:14
-   |
-LL |     type T = impl Copy;  // error: unconstrained opaque type
-   |              ^^^^^^^^^
-   |
-   = note: `T` must be used in combination with a concrete type within the same module
-
-error: aborting due to previous error
-

src/test/ui/type-alias-impl-trait/issue-96572-unconstrained-mismatch.rs

@@ -0,0 +1,10 @@
+#![feature(type_alias_impl_trait)]
+
+fn main() {
+    type T = impl Copy;
+    let foo: T = Some((1u32, 2u32));
+    match foo {
+        None => (),
+        Some((a, b, c)) => (), //~ ERROR mismatched types
+    }
+}

src/test/ui/type-alias-impl-trait/issue-96572-unconstrained-mismatch.stderr

@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-96572-unconstrained-mismatch.rs:8:14
+   |
+LL |     match foo {
+   |           --- this expression has type `T`
+LL |         None => (),
+LL |         Some((a, b, c)) => (),
+   |              ^^^^^^^^^ expected a tuple with 2 elements, found one with 3 elements
+   |
+   = note: expected tuple `(u32, u32)`
+              found tuple `(_, _, _)`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/type-alias-impl-trait/issue-96572-unconstrained.rs

@@ -0,0 +1,92 @@
+#![feature(type_alias_impl_trait)]
+// check-pass
+
+fn main() {
+    type T = impl Copy;
+    let foo: T = Some((1u32, 2u32));
+    match foo {
+        None => (),
+        Some((a, b)) => (),
+    }
+}
+
+fn upvar() {
+    #[derive(Copy, Clone)]
+    struct Foo((u32, u32));
+
+    type T = impl Copy;
+    let foo: T = Foo((1u32, 2u32));
+    let x = move || {
+        let Foo((a, b)) = foo;
+    };
+}
+
+fn enum_upvar() {
+    type T = impl Copy;
+    let foo: T = Some((1u32, 2u32));
+    let x = move || {
+        match foo {
+            None => (),
+            Some((a, b)) => (),
+        }
+    };
+}
+
+fn r#struct() {
+    #[derive(Copy, Clone)]
+    struct Foo((u32, u32));
+
+    type U = impl Copy;
+    let foo: U = Foo((1u32, 2u32));
+    let Foo((a, b)) = foo;
+}
+
+mod only_pattern {
+    type T = impl Copy;
+
+    fn foo(foo: T) {
+        let (mut x, mut y) = foo;
+        x = 42;
+        y = "foo";
+    }
+
+    type U = impl Copy;
+
+    fn bar(bar: Option<U>) {
+        match bar {
+            Some((mut x, mut y)) => {
+                x = 42;
+                y = "foo";
+            }
+            None => {}
+        }
+    }
+}
+
+mod only_pattern_rpit {
+    #[allow(unconditional_recursion)]
+    fn foo(b: bool) -> impl Copy {
+        let (mut x, mut y) = foo(false);
+        x = 42;
+        y = "foo";
+        if b {
+            panic!()
+        } else {
+            foo(true)
+        }
+    }
+
+    fn bar(b: bool) -> Option<impl Copy> {
+        if b {
+            return None;
+        }
+        match bar(!b) {
+            Some((mut x, mut y)) => {
+                x = 42;
+                y = "foo";
+            }
+            None => {}
+        }
+        None
+    }
+}

src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs

@@ -260,6 +260,7 @@ fn check_place<'tcx>(tcx: TyCtxt<'tcx>, place: Place<'tcx>, span: Span, body: &B
                 }
             },
             ProjectionElem::ConstantIndex { .. }
+            | ProjectionElem::OpaqueCast(..)
             | ProjectionElem::Downcast(..)
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Deref