Revert "Rollup merge of #98582 - oli-obk:unconstrained_opaque_type, r=estebank"

This reverts commit 6f8fb911ad504b77549cf3256a09465621beab9d, reversing
changes made to 7210e46dc69a4b197a313d093fe145722c248b7d.

5 files changed, 3 insertions, 24 deletions

diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 0b5d23be58d..f61cb7e8c47 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1397,7 +1397,6 @@ impl<V, T> ProjectionElem<V, T> {
 
             Self::Field(_, _)
             | Self::Index(_)
-            | Self::OpaqueCast(_)
             | Self::ConstantIndex { .. }
             | Self::Subslice { .. }
             | Self::Downcast(_, _) => false,
@@ -1575,9 +1574,7 @@ impl Debug for Place<'_> {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
         for elem in self.projection.iter().rev() {
             match elem {
-                ProjectionElem::OpaqueCast(_)
-                | ProjectionElem::Downcast(_, _)
-                | ProjectionElem::Field(_, _) => {
+                ProjectionElem::Downcast(_, _) | ProjectionElem::Field(_, _) => {
                     write!(fmt, "(").unwrap();
                 }
                 ProjectionElem::Deref => {
@@ -1593,9 +1590,6 @@ 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)?;
                 }
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 263c2ca3c70..510316c778b 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -754,9 +754,6 @@ 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
@@ -859,10 +856,6 @@ 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
diff --git a/compiler/rustc_middle/src/mir/tcx.rs b/compiler/rustc_middle/src/mir/tcx.rs
index c6975df45ef..fd3359ea80f 100644
--- a/compiler/rustc_middle/src/mir/tcx.rs
+++ b/compiler/rustc_middle/src/mir/tcx.rs
@@ -57,7 +57,7 @@ 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, |_, ty| ty)
+        self.projection_ty_core(tcx, ty::ParamEnv::empty(), &elem, |_, _, ty| ty)
     }
 
     /// `place_ty.projection_ty_core(tcx, elem, |...| { ... })`
@@ -71,7 +71,6 @@ 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,
@@ -110,7 +109,6 @@ 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
diff --git a/compiler/rustc_middle/src/mir/type_foldable.rs b/compiler/rustc_middle/src/mir/type_foldable.rs
index a73ef23e281..82a6b0c506f 100644
--- a/compiler/rustc_middle/src/mir/type_foldable.rs
+++ b/compiler/rustc_middle/src/mir/type_foldable.rs
@@ -182,7 +182,6 @@ impl<'tcx> TypeFoldable<'tcx> for PlaceElem<'tcx> {
         Ok(match self {
             Deref => Deref,
             Field(f, ty) => Field(f, ty.try_fold_with(folder)?),
-            OpaqueCast(ty) => OpaqueCast(ty.try_fold_with(folder)?),
             Index(v) => Index(v.try_fold_with(folder)?),
             Downcast(symbol, variantidx) => Downcast(symbol, variantidx),
             ConstantIndex { offset, min_length, from_end } => {
diff --git a/compiler/rustc_middle/src/mir/visit.rs b/compiler/rustc_middle/src/mir/visit.rs
index e5599fb15ad..d285728ec07 100644
--- a/compiler/rustc_middle/src/mir/visit.rs
+++ b/compiler/rustc_middle/src/mir/visit.rs
@@ -1064,11 +1064,6 @@ 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 { .. }
@@ -1138,7 +1133,7 @@ macro_rules! visit_place_fns {
             location: Location,
         ) {
             match elem {
-                ProjectionElem::OpaqueCast(ty) | ProjectionElem::Field(_, ty) => {
+                ProjectionElem::Field(_field, ty) => {
                     self.visit_ty(ty, TyContext::Location(location));
                 }
                 ProjectionElem::Index(local) => {