use ProjectionFragment(Ref) type alias

makes it easier to change in the future, which will be needed for borrowck and co

Author: beepster4096

compiler/rustc_middle/src/mir/statement.rs

@@ -161,7 +161,7 @@ impl<'tcx> PlaceTy<'tcx> {
     pub fn projection_chain_ty(
         self,
         tcx: TyCtxt<'tcx>,
-        chain: &[&List<PlaceElem<'tcx>>],
+        chain: &[ProjectionFragment<'tcx>],
     ) -> PlaceTy<'tcx> {
         chain
             .iter()
@@ -556,6 +556,13 @@ impl From<Local> for PlaceRef<'_> {
     }
 }
 
+// In the future this will also have the type being projected alongside it.
+// This will be needed to represent derefs of non-pointer types like `Box`.
+//
+// (`Ty::builtin_deref` currently works on `Box` but that will be changed too)
+pub type ProjectionFragment<'tcx> = &'tcx List<PlaceElem<'tcx>>;
+pub type ProjectionFragmentRef<'tcx> = &'tcx [PlaceElem<'tcx>];
+
 /// A place possibly containing derefs in the middle of its projection by chaining projection lists.
 ///
 /// In `AnalysisPhase::PostCleanup` and later, [`Place`] and [`PlaceRef`] cannot represent these
@@ -567,15 +574,15 @@ pub struct CompoundPlace<'tcx> {
     /// - All segments in the chain other than the first must start with a deref.
     /// - Derefs may only appear at the start of a segment.
     /// - No segment may be empty.
-    pub projection_chain: &'tcx List<&'tcx List<PlaceElem<'tcx>>>,
+    pub projection_chain: &'tcx List<ProjectionFragment<'tcx>>,
 }
 
 /// Borrowed form of [`CompoundPlace`].
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct CompoundPlaceRef<'tcx> {
     pub local: Local,
-    pub projection_chain_base: &'tcx [&'tcx List<PlaceElem<'tcx>>],
-    pub last_projection: &'tcx [PlaceElem<'tcx>],
+    pub projection_chain_base: &'tcx [ProjectionFragment<'tcx>],
+    pub last_projection: ProjectionFragmentRef<'tcx>,
 }
 
 // these impls are bare-bones for now

compiler/rustc_middle/src/ty/context.rs

@@ -68,7 +68,7 @@ use crate::metadata::ModChild;
 use crate::middle::codegen_fn_attrs::{CodegenFnAttrs, TargetFeature};
 use crate::middle::resolve_bound_vars;
 use crate::mir::interpret::{self, Allocation, ConstAllocation};
-use crate::mir::{Body, Local, Place, PlaceElem, ProjectionKind, Promoted};
+use crate::mir::{Body, Local, Place, PlaceElem, ProjectionFragment, ProjectionKind, Promoted};
 use crate::query::plumbing::QuerySystem;
 use crate::query::{IntoQueryParam, LocalCrate, Providers, TyCtxtAt};
 use crate::thir::Thir;
@@ -2781,7 +2781,7 @@ slice_interners!(
     poly_existential_predicates: intern_poly_existential_predicates(PolyExistentialPredicate<'tcx>),
     projs: pub mk_projs(ProjectionKind),
     place_elems: pub mk_place_elems(PlaceElem<'tcx>),
-    place_elem_chains: pub mk_place_elem_chain(&'tcx List<PlaceElem<'tcx>>),
+    place_elem_chains: pub mk_place_elem_chain(ProjectionFragment<'tcx>),
     bound_variable_kinds: pub mk_bound_variable_kinds(ty::BoundVariableKind),
     fields: pub mk_fields(FieldIdx),
     local_def_ids: intern_local_def_ids(LocalDefId),
@@ -3175,7 +3175,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn mk_place_elem_chain_from_iter<I, T>(self, iter: I) -> T::Output
     where
         I: Iterator<Item = T>,
-        T: CollectAndApply<&'tcx List<PlaceElem<'tcx>>, &'tcx List<&'tcx List<PlaceElem<'tcx>>>>,
+        T: CollectAndApply<&'tcx List<PlaceElem<'tcx>>, &'tcx List<ProjectionFragment<'tcx>>>,
     {
         T::collect_and_apply(iter, |xs| self.mk_place_elem_chain(xs))
     }

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -13,7 +13,7 @@ use rustc_span::source_map::Spanned;
 use rustc_type_ir::{ConstKind, TypeFolder, VisitorResult, try_visit};
 
 use super::{GenericArg, GenericArgKind, Pattern, Region};
-use crate::mir::PlaceElem;
+use crate::mir::{PlaceElem, ProjectionFragment};
 use crate::ty::print::{FmtPrinter, Printer, with_no_trimmed_paths};
 use crate::ty::{
     self, FallibleTypeFolder, Lift, Term, TermKind, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
@@ -797,7 +797,7 @@ macro_rules! list_fold {
 list_fold! {
     &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> : mk_poly_existential_predicates,
     &'tcx ty::List<PlaceElem<'tcx>> : mk_place_elems,
-    &'tcx ty::List<&'tcx ty::List<PlaceElem<'tcx>>> : mk_place_elem_chain,
+    &'tcx ty::List<ProjectionFragment<'tcx>> : mk_place_elem_chain,
     &'tcx ty::List<ty::Pattern<'tcx>> : mk_patterns,
     &'tcx ty::List<ty::ArgOutlivesPredicate<'tcx>> : mk_outlives,
 }