Rollup merge of #107486 - compiler-errors:bound-ty-keep-name, r=oli-obk

Track bound types like bound regions

When we instantiate bound types into placeholder types, we throw away the names for some reason. These names are particularly useful for error reporting once we have `for<T>` binders.

r? types

compiler/rustc_middle/src/ty/fold.rs

@@ -610,7 +610,9 @@ impl<'tcx> TyCtxt<'tcx> {
                 let index = entry.index();
                 let var = ty::BoundVar::from_usize(index);
                 let kind = entry
-                    .or_insert_with(|| ty::BoundVariableKind::Ty(ty::BoundTyKind::Anon))
+                    .or_insert_with(|| {
+                        ty::BoundVariableKind::Ty(ty::BoundTyKind::Anon(index as u32))
+                    })
                     .expect_ty();
                 self.tcx.mk_ty(ty::Bound(ty::INNERMOST, BoundTy { var, kind }))
             }

compiler/rustc_middle/src/ty/mod.rs

@@ -1369,7 +1369,7 @@ pub struct Placeholder<T> {
 
 pub type PlaceholderRegion = Placeholder<BoundRegionKind>;
 
-pub type PlaceholderType = Placeholder<BoundVar>;
+pub type PlaceholderType = Placeholder<BoundTyKind>;
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 #[derive(TyEncodable, TyDecodable, PartialOrd, Ord)]

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -698,8 +698,10 @@ pub trait PrettyPrinter<'tcx>:
             ty::Error(_) => p!("[type error]"),
             ty::Param(ref param_ty) => p!(print(param_ty)),
             ty::Bound(debruijn, bound_ty) => match bound_ty.kind {
-                ty::BoundTyKind::Anon => self.pretty_print_bound_var(debruijn, bound_ty.var)?,
-                ty::BoundTyKind::Param(p) => p!(write("{}", p)),
+                ty::BoundTyKind::Anon(bv) => {
+                    self.pretty_print_bound_var(debruijn, ty::BoundVar::from_u32(bv))?
+                }
+                ty::BoundTyKind::Param(_, s) => p!(write("{}", s)),
             },
             ty::Adt(def, substs) => {
                 p!(print_def_path(def.did(), substs));

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -240,6 +240,7 @@ TrivialTypeTraversalAndLiftImpls! {
     crate::ty::AssocKind,
     crate::ty::AliasKind,
     crate::ty::Placeholder<crate::ty::BoundRegionKind>,
+    crate::ty::Placeholder<crate::ty::BoundTyKind>,
     crate::ty::ClosureKind,
     crate::ty::FreeRegion,
     crate::ty::InferTy,

compiler/rustc_middle/src/ty/sty.rs

@@ -1504,13 +1504,22 @@ pub struct BoundTy {
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub enum BoundTyKind {
-    Anon,
-    Param(Symbol),
+    Anon(u32),
+    Param(DefId, Symbol),
+}
+
+impl BoundTyKind {
+    pub fn expect_anon(self) -> u32 {
+        match self {
+            BoundTyKind::Anon(i) => i,
+            _ => bug!(),
+        }
+    }
 }
 
 impl From<BoundVar> for BoundTy {
     fn from(var: BoundVar) -> Self {
-        BoundTy { var, kind: BoundTyKind::Anon }
+        BoundTy { var, kind: BoundTyKind::Anon(var.as_u32()) }
     }
 }