---

yaml
---
r: 213937
b: refs/heads/tmp
c: d914831
h: refs/heads/master
i:
  213935: ae1791a
v: v3

Author: eddyb

[refs]

@@ -32,7 +32,7 @@ refs/heads/building: 126db549b038c84269a1e4fe46f051b2c15d6970
 refs/heads/beta: e99b1404e9b3f60dc496a8eb0a6ce9fecc7ac583
 refs/heads/windistfix: 7608dbad651f02e837ed05eef3d74a6662a6e928
 refs/tags/1.0.0-alpha: e42bd6d93a1d3433c486200587f8f9e12590a4d7
-refs/heads/tmp: 0b58fdf9252ccd08bf610e13625f49380e769e06
+refs/heads/tmp: d9148311451d38e831dcaa15548fb6ac6f6450b9
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f
 refs/tags/homu-tmp: d8a9570154dfbc4032cb3a6ba8b51c6256518dcd
 refs/heads/gate: 97c84447b65164731087ea82685580cc81424412

branches/tmp/src/librustc/middle/ty.rs

@@ -816,6 +816,12 @@ impl<'tcx> ctxt<'tcx> {
 /// provided ty::ctxt<'tcx>.
 /// This can be done, for example, for Ty<'tcx> or &'tcx Substs<'tcx>
 /// by looking them up in their respective interners.
+/// None is returned if the value or one of the components is not part
+/// of the provided context.
+/// For Ty, None can be returned if either the type interner doesn't
+/// contain the TypeVariants key or if the address of the interned
+/// pointer differs. The latter case is possible if a primitive type,
+/// e.g. `()` or `u8`, was interned in a different context.
 pub trait Lift<'tcx> {
     type Lifted;
     fn lift_to_tcx(&self, tcx: &ctxt<'tcx>) -> Option<Self::Lifted>;
@@ -3016,6 +3022,10 @@ impl<'tcx> CommonTypes<'tcx> {
     }
 }
 
+/// Create a type context and call the closure with a `&ty::ctxt` reference
+/// to the context. The closure enforces that the type context and any interned
+/// value (types, substs, etc.) can only be used while `ty::tls` has a valid
+/// reference to the context, to allow formatting values that need it.
 pub fn with_ctxt<'tcx, F, R>(s: Session,
                              arenas: &'tcx CtxtArenas<'tcx>,
                              def_map: DefMap,