Substitute free lifetimes in `Self::T`

Fixes #27281

3 files changed, 63 insertions, 44 deletions

diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index c448af2288a..d516c648d7e 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -60,7 +60,7 @@ use middle::traits;
 use middle::ty::{self, RegionEscape, Ty, ToPredicate, HasTypeFlags};
 use middle::ty_fold;
 use require_c_abi_if_variadic;
-use rscope::{self, UnelidableRscope, RegionScope, ElidableRscope, ExplicitRscope,
+use rscope::{self, UnelidableRscope, RegionScope, ElidableRscope,
              ObjectLifetimeDefaultRscope, ShiftedRscope, BindingRscope,
              ElisionFailureInfo, ElidedLifetime};
 use util::common::{ErrorReported, FN_OUTPUT_NAME};
@@ -1208,40 +1208,33 @@ fn associated_path_def_to_ty<'tcx>(this: &AstConv<'tcx>,
         (_, def::DefSelfTy(Some(trait_did), Some((impl_id, _)))) => {
             // `Self` in an impl of a trait - we have a concrete self type and a
             // trait reference.
-            match tcx.map.expect_item(impl_id).node {
-                ast::ItemImpl(_, _, _, Some(ref trait_ref), _, _) => {
-                    if this.ensure_super_predicates(span, trait_did).is_err() {
-                        return (tcx.types.err, ty_path_def);
-                    }
+            let trait_ref = tcx.impl_trait_ref(ast_util::local_def(impl_id)).unwrap();
+            let trait_ref = if let Some(free_substs) = this.get_free_substs() {
+                trait_ref.subst(tcx, free_substs)
+            } else {
+                trait_ref
+            };
 
-                    let trait_segment = &trait_ref.path.segments.last().unwrap();
-                    let trait_ref = ast_path_to_mono_trait_ref(this,
-                                                               &ExplicitRscope,
-                                                               span,
-                                                               PathParamMode::Explicit,
-                                                               trait_did,
-                                                               Some(ty),
-                                                               trait_segment);
-
-                    let candidates: Vec<ty::PolyTraitRef> =
-                        traits::supertraits(tcx, ty::Binder(trait_ref.clone()))
-                        .filter(|r| this.trait_defines_associated_type_named(r.def_id(),
-                                                                             assoc_name))
-                        .collect();
-
-                    match one_bound_for_assoc_type(tcx,
-                                                   candidates,
-                                                   "Self",
-                                                   &token::get_name(assoc_name),
-                                                   span) {
-                        Ok(bound) => bound,
-                        Err(ErrorReported) => return (tcx.types.err, ty_path_def),
-                    }
-                }
-                _ => unreachable!()
+            if this.ensure_super_predicates(span, trait_did).is_err() {
+                return (tcx.types.err, ty_path_def);
+            }
+
+            let candidates: Vec<ty::PolyTraitRef> =
+                traits::supertraits(tcx, ty::Binder(trait_ref))
+                .filter(|r| this.trait_defines_associated_type_named(r.def_id(),
+                                                                     assoc_name))
+                .collect();
+
+            match one_bound_for_assoc_type(tcx,
+                                           candidates,
+                                           "Self",
+                                           &token::get_name(assoc_name),
+                                           span) {
+                Ok(bound) => bound,
+                Err(ErrorReported) => return (tcx.types.err, ty_path_def),
             }
         }
-        (&ty::TyParam(_), def::DefSelfTy(Some(trait_did),  None)) => {
+        (&ty::TyParam(_), def::DefSelfTy(Some(trait_did), None)) => {
             assert_eq!(trait_did.krate, ast::LOCAL_CRATE);
             match find_bound_for_assoc_item(this,
                                             trait_did.node,
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index 5a6519cb4b7..b003f0fc4f8 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -836,6 +836,18 @@ fn convert_item(ccx: &CrateCtxt, it: &ast::Item) {
                                                 ty: selfty });
             tcx.predicates.borrow_mut().insert(local_def(it.id),
                                                ty_predicates.clone());
+            if let &Some(ref ast_trait_ref) = opt_trait_ref {
+                tcx.impl_trait_refs.borrow_mut().insert(
+                    local_def(it.id),
+                    Some(astconv::instantiate_mono_trait_ref(&ccx.icx(&ty_predicates),
+                                                             &ExplicitRscope,
+                                                             ast_trait_ref,
+                                                             Some(selfty)))
+                        );
+            } else {
+                tcx.impl_trait_refs.borrow_mut().insert(local_def(it.id), None);
+            }
+
 
             // If there is a trait reference, treat the methods as always public.
             // This is to work around some incorrect behavior in privacy checking:
@@ -935,18 +947,6 @@ fn convert_item(ccx: &CrateCtxt, it: &ast::Item) {
                 }
             }
 
-            if let &Some(ref ast_trait_ref) = opt_trait_ref {
-                tcx.impl_trait_refs.borrow_mut().insert(
-                    local_def(it.id),
-                    Some(astconv::instantiate_mono_trait_ref(&ccx.icx(&ty_predicates),
-                                                             &ExplicitRscope,
-                                                             ast_trait_ref,
-                                                             Some(selfty)))
-                        );
-            } else {
-                tcx.impl_trait_refs.borrow_mut().insert(local_def(it.id), None);
-            }
-
             enforce_impl_params_are_constrained(tcx,
                                                 generics,
                                                 local_def(it.id),
diff --git a/src/test/run-pass/issue-27281.rs b/src/test/run-pass/issue-27281.rs
new file mode 100644
index 00000000000..c84fc0fffe3
--- /dev/null
+++ b/src/test/run-pass/issue-27281.rs
@@ -0,0 +1,26 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub trait Trait<'a> {
+    type T;
+    type U;
+    fn foo(&self, s: &'a ()) -> &'a ();
+}
+
+impl<'a> Trait<'a> for () {
+    type T = &'a ();
+    type U = Self::T;
+
+    fn foo(&self, s: &'a ()) -> &'a () {
+        let t: Self::T = s; t
+    }
+}
+
+fn main() {}