From 94ab344537f0c0cc77a44b7a1265041ac296d7c1 Mon Sep 17 00:00:00 2001
From: Tyler Mandry <tmandry@gmail.com>
Date: Sat, 14 Apr 2018 18:11:31 -0500
Subject: [PATCH] chalkify: Fix lowering of traits with supertraits

---
 src/librustc_traits/lowering.rs               | 12 +++++++++--
 .../ui/chalkify/lower_trait_supertrait.rs     | 21 +++++++++++++++++++
 .../ui/chalkify/lower_trait_supertrait.stderr | 14 +++++++++++++
 3 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/chalkify/lower_trait_supertrait.rs
 create mode 100644 src/test/ui/chalkify/lower_trait_supertrait.stderr

diff --git a/src/librustc_traits/lowering.rs b/src/librustc_traits/lowering.rs
index df6793e8a604c..afa999f10f321 100644
--- a/src/librustc_traits/lowering.rs
+++ b/src/librustc_traits/lowering.rs
@@ -172,11 +172,19 @@ fn program_clauses_for_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefI
     // ```
 
     // `FromEnv(WC) :- FromEnv(Self: Trait<P1..Pn>)`, for each where clause WC
-    // FIXME: Remove the [1..] slice; this is a hack because the query
+    // FIXME: Remove the filter; this is a hack because the query
     // predicates_of currently includes the trait itself (`Self: Trait<P1..Pn>`).
     let where_clauses = &tcx.predicates_of(def_id).predicates;
     let implied_bound_clauses =
-        where_clauses[1..].into_iter()
+        where_clauses.into_iter()
+        .filter(|wc| {
+            if let ty::Predicate::Trait(pred) = wc {
+                if pred.skip_binder().def_id() == def_id {
+                    return false;
+                }
+            }
+            true
+        })
         .map(|wc| implied_bound_from_trait(tcx, trait_pred, wc));
 
     Lrc::new(tcx.mk_clauses(clauses.chain(implied_bound_clauses)))
diff --git a/src/test/ui/chalkify/lower_trait_supertrait.rs b/src/test/ui/chalkify/lower_trait_supertrait.rs
new file mode 100644
index 0000000000000..6a885b5f9a983
--- /dev/null
+++ b/src/test/ui/chalkify/lower_trait_supertrait.rs
@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+#![feature(rustc_attrs)]
+
+trait Bar {}
+
+#[rustc_dump_program_clauses] //~ ERROR Implemented
+                              //~^ ERROR FromEnv
+trait Foo: Bar {}
+
+fn main() {
+    println!("hello");
+}
diff --git a/src/test/ui/chalkify/lower_trait_supertrait.stderr b/src/test/ui/chalkify/lower_trait_supertrait.stderr
new file mode 100644
index 0000000000000..8ea1dd6ee1614
--- /dev/null
+++ b/src/test/ui/chalkify/lower_trait_supertrait.stderr
@@ -0,0 +1,14 @@
+error: Implemented(Self: Foo) :- FromEnv(Self: Foo).
+  --> $DIR/lower_trait_supertrait.rs:15:1
+   |
+LL | #[rustc_dump_program_clauses] //~ ERROR Implemented
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: FromEnv(Self: Bar) :- FromEnv(Self: Foo).
+  --> $DIR/lower_trait_supertrait.rs:15:1
+   |
+LL | #[rustc_dump_program_clauses] //~ ERROR Implemented
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+