symbol_names: treat ReifyShim like VtableShim.

src/librustc/ty/instance.rs

@@ -406,10 +406,6 @@ impl<'tcx> Instance<'tcx> {
             | InstanceDef::VtableShim(..) => Some(self.substs),
         }
     }
-
-    pub fn is_vtable_shim(&self) -> bool {
-        if let InstanceDef::VtableShim(..) = self.def { true } else { false }
-    }
 }
 
 fn needs_fn_once_adapter_shim(

src/librustc_symbol_mangling/legacy.rs

@@ -59,10 +59,14 @@ pub(super) fn mangle(
         .print_def_path(def_id, &[])
         .unwrap();
 
-    if instance.is_vtable_shim() {
+    if let ty::InstanceDef::VtableShim(..) = instance.def {
         let _ = printer.write_str("{{vtable-shim}}");
     }
 
+    if let ty::InstanceDef::ReifyShim(..) = instance.def {
+        let _ = printer.write_str("{{reify-shim}}");
+    }
+
     printer.path.finish(hash)
 }
 
@@ -123,7 +127,8 @@ fn get_symbol_hash<'tcx>(
         }
 
         // We want to avoid accidental collision between different types of instances.
-        // Especially, VtableShim may overlap with its original instance without this.
+        // Especially, `VtableShim`s and `ReifyShim`s may overlap with their original
+        // instances without this.
         discriminant(&instance.def).hash_stable(&mut hcx, &mut hasher);
     });
 

src/librustc_symbol_mangling/v0.rs

@@ -34,8 +34,17 @@ pub(super) fn mangle(
         binders: vec![],
         out: String::from(prefix),
     };
-    cx = if instance.is_vtable_shim() {
-        cx.path_append_ns(|cx| cx.print_def_path(def_id, substs), 'S', 0, "").unwrap()
+
+    // Append `::{shim:...#0}` to shims that can coexist with a non-shim instance.
+    let shim_kind = match instance.def {
+        ty::InstanceDef::VtableShim(_) => Some("vtable"),
+        ty::InstanceDef::ReifyShim(_) => Some("reify"),
+
+        _ => None,
+    };
+
+    cx = if let Some(shim_kind) = shim_kind {
+        cx.path_append_ns(|cx| cx.print_def_path(def_id, substs), 'S', 0, shim_kind).unwrap()
     } else {
         cx.print_def_path(def_id, substs).unwrap()
     };