Auto merge of rust-lang#105905 - lqd:revert-103880, r=jackh726

Revert rust-lang#103880 "Use non-ascribed type as field's type in mir"

This PR prepares a revert for rust-lang#103880 to fix rust-lang#105809, rust-lang#105881, rust-lang#105886 and others (like the duplicates of the first one), in case an actual fix can't get done today.

I've also added the MCVE from rust-lang#105809. There is no MCVE for the rust-lang#105881 and rust-lang#105886 ICEs yet however, so there are no tests for them here, although we'll need one before relanding the original changes.

Were this PR to land, it would also reopen rust-lang#96514 as it was fixed by the original PR.

Opening as draft to allow time for a possible fix.

r? `@jackh726`

compiler/rustc_middle/src/mir/mod.rs

@@ -1488,7 +1488,7 @@ impl<'tcx> StatementKind<'tcx> {
 ///////////////////////////////////////////////////////////////////////////
 // Places
 
-impl<V, T, U> ProjectionElem<V, T, U> {
+impl<V, T> ProjectionElem<V, T> {
     /// Returns `true` if the target of this projection may refer to a different region of memory
     /// than the base.
     fn is_indirect(&self) -> bool {
@@ -1517,7 +1517,7 @@ impl<V, T, U> ProjectionElem<V, T, U> {
 
 /// Alias for projections as they appear in `UserTypeProjection`, where we
 /// need neither the `V` parameter for `Index` nor the `T` for `Field`.
-pub type ProjectionKind = ProjectionElem<(), (), ()>;
+pub type ProjectionKind = ProjectionElem<(), ()>;
 
 rustc_index::newtype_index! {
     /// A [newtype'd][wrapper] index type in the MIR [control-flow graph][CFG]

compiler/rustc_middle/src/mir/syntax.rs

@@ -890,18 +890,11 @@ pub struct Place<'tcx> {
     pub projection: &'tcx List<PlaceElem<'tcx>>,
 }
 
-/// The different kinds of projections that can be used in the projection of a `Place`.
-///
-/// `T1` is the generic type for a field projection. For an actual projection on a `Place`
-/// this parameter will always be `Ty`, but the field type can be unavailable when
-/// building (by using `PlaceBuilder`) places that correspond to upvars.
-/// `T2` is the generic type for an `OpaqueCast` (is generic since it's abstracted over
-/// in dataflow analysis, see `AbstractElem`).
 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
-pub enum ProjectionElem<V, T1, T2> {
+pub enum ProjectionElem<V, T> {
     Deref,
-    Field(Field, T1),
+    Field(Field, T),
     /// Index into a slice/array.
     ///
     /// Note that this does not also dereference, and so it does not exactly correspond to slice
@@ -957,36 +950,12 @@ pub enum ProjectionElem<V, T1, T2> {
 
     /// Like an explicit cast from an opaque type to a concrete type, but without
     /// requiring an intermediate variable.
-    OpaqueCast(T2),
+    OpaqueCast(T),
 }
 
 /// Alias for projections as they appear in places, where the base is a place
 /// and the index is a local.
-pub type PlaceElem<'tcx> = ProjectionElem<Local, Ty<'tcx>, Ty<'tcx>>;
-
-/// Alias for projections that appear in `PlaceBuilder::Upvar`, for which
-/// we cannot provide any field types.
-pub type UpvarProjectionElem<'tcx> = ProjectionElem<Local, (), Ty<'tcx>>;
-
-impl<'tcx> From<PlaceElem<'tcx>> for UpvarProjectionElem<'tcx> {
-    fn from(elem: PlaceElem<'tcx>) -> Self {
-        match elem {
-            ProjectionElem::Deref => ProjectionElem::Deref,
-            ProjectionElem::Field(field, _) => ProjectionElem::Field(field, ()),
-            ProjectionElem::Index(v) => ProjectionElem::Index(v),
-            ProjectionElem::ConstantIndex { offset, min_length, from_end } => {
-                ProjectionElem::ConstantIndex { offset, min_length, from_end }
-            }
-            ProjectionElem::Subslice { from, to, from_end } => {
-                ProjectionElem::Subslice { from, to, from_end }
-            }
-            ProjectionElem::Downcast(opt_sym, variant_idx) => {
-                ProjectionElem::Downcast(opt_sym, variant_idx)
-            }
-            ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty),
-        }
-    }
-}
+pub type PlaceElem<'tcx> = ProjectionElem<Local, Ty<'tcx>>;
 
 ///////////////////////////////////////////////////////////////////////////
 // Operands

compiler/rustc_middle/src/mir/tcx.rs

@@ -28,8 +28,8 @@ impl<'tcx> PlaceTy<'tcx> {
     /// `place_ty.field_ty(tcx, f)` computes the type at a given field
     /// of a record or enum-variant. (Most clients of `PlaceTy` can
     /// instead just extract the relevant type directly from their
-    /// `PlaceElem`, but some instances of `ProjectionElem<V, T1, T2>` do
-    /// not carry a `Ty` for `T1` or `T2`.)
+    /// `PlaceElem`, but some instances of `ProjectionElem<V, T>` do
+    /// not carry a `Ty` for `T`.)
     ///
     /// Note that the resulting type has not been normalized.
     pub fn field_ty(self, tcx: TyCtxt<'tcx>, f: Field) -> Ty<'tcx> {
@@ -64,18 +64,17 @@ impl<'tcx> PlaceTy<'tcx> {
     /// `Ty` or downcast variant corresponding to that projection.
     /// The `handle_field` callback must map a `Field` to its `Ty`,
     /// (which should be trivial when `T` = `Ty`).
-    pub fn projection_ty_core<V, T1, T2>(
+    pub fn projection_ty_core<V, T>(
         self,
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        elem: &ProjectionElem<V, T1, T2>,
-        mut handle_field: impl FnMut(&Self, Field, T1) -> Ty<'tcx>,
-        mut handle_opaque_cast: impl FnMut(&Self, T2) -> Ty<'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,
-        T1: ::std::fmt::Debug + Copy,
-        T2: ::std::fmt::Debug + Copy,
+        T: ::std::fmt::Debug + Copy,
     {
         if self.variant_index.is_some() && !matches!(elem, ProjectionElem::Field(..)) {
             bug!("cannot use non field projection on downcasted place")