From a5cfc4011d6981437ea65ec5adc346b114e29a52 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Mon, 30 Sep 2019 18:34:48 -0700
Subject: [PATCH 1/2] Avoid ICE on ReFree region from malformed code

---
 src/librustc_typeck/outlives/utils.rs           | 17 +++++++++++++++--
 src/test/ui/associated-types/issue-64855.rs     |  8 ++++++++
 src/test/ui/associated-types/issue-64855.stderr |  9 +++++++++
 3 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/associated-types/issue-64855.rs
 create mode 100644 src/test/ui/associated-types/issue-64855.stderr

diff --git a/src/librustc_typeck/outlives/utils.rs b/src/librustc_typeck/outlives/utils.rs
index d83c97b522c67..cd92189176eff 100644
--- a/src/librustc_typeck/outlives/utils.rs
+++ b/src/librustc_typeck/outlives/utils.rs
@@ -1,6 +1,7 @@
 use rustc::ty::outlives::Component;
 use rustc::ty::subst::{GenericArg, GenericArgKind};
 use rustc::ty::{self, Region, RegionKind, Ty, TyCtxt};
+use syntax_pos::DUMMY_SP;
 use smallvec::smallvec;
 use std::collections::BTreeSet;
 
@@ -161,9 +162,21 @@ fn is_free_region(tcx: TyCtxt<'_>, region: Region<'_>) -> bool {
         // ignore it.  We can't put it on the struct header anyway.
         RegionKind::ReLateBound(..) => false,
 
+        // This can appear with malformed code (#64855):
+        //
+        //     struct Bar<T>(<Self as Foo>::Type) where Self: ;
+        //
+        // We accept it only to avoid an ICE.
+        RegionKind::ReEmpty => {
+            tcx.sess.delay_span_bug(
+                DUMMY_SP,
+                &format!("unexpected region in outlives inference: {:?}", region),
+            );
+            false
+        }
+
         // These regions don't appear in types from type declarations:
-        RegionKind::ReEmpty
-        | RegionKind::ReErased
+        RegionKind::ReErased
         | RegionKind::ReClosureBound(..)
         | RegionKind::ReScope(..)
         | RegionKind::ReVar(..)
diff --git a/src/test/ui/associated-types/issue-64855.rs b/src/test/ui/associated-types/issue-64855.rs
new file mode 100644
index 0000000000000..81cf3ae6e83b6
--- /dev/null
+++ b/src/test/ui/associated-types/issue-64855.rs
@@ -0,0 +1,8 @@
+pub trait Foo {
+    type Type;
+}
+
+pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
+//~^ ERROR the trait bound `Bar<T>: Foo` is not satisfied
+
+fn main() {}
diff --git a/src/test/ui/associated-types/issue-64855.stderr b/src/test/ui/associated-types/issue-64855.stderr
new file mode 100644
index 0000000000000..6ad795c11176d
--- /dev/null
+++ b/src/test/ui/associated-types/issue-64855.stderr
@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `Bar<T>: Foo` is not satisfied
+  --> $DIR/issue-64855.rs:5:19
+   |
+LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
+   |                   ^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `Bar<T>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

From de815653eda51093d31a41ada7041f48d7417866 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Wed, 2 Oct 2019 15:53:36 -0700
Subject: [PATCH 2/2] review comments

---
 src/librustc_typeck/outlives/utils.rs         | 14 +++-----------
 src/test/ui/associated-types/issue-64855-2.rs |  5 +++++
 2 files changed, 8 insertions(+), 11 deletions(-)
 create mode 100644 src/test/ui/associated-types/issue-64855-2.rs

diff --git a/src/librustc_typeck/outlives/utils.rs b/src/librustc_typeck/outlives/utils.rs
index cd92189176eff..d34605dc482a3 100644
--- a/src/librustc_typeck/outlives/utils.rs
+++ b/src/librustc_typeck/outlives/utils.rs
@@ -1,7 +1,6 @@
 use rustc::ty::outlives::Component;
 use rustc::ty::subst::{GenericArg, GenericArgKind};
 use rustc::ty::{self, Region, RegionKind, Ty, TyCtxt};
-use syntax_pos::DUMMY_SP;
 use smallvec::smallvec;
 use std::collections::BTreeSet;
 
@@ -162,18 +161,11 @@ fn is_free_region(tcx: TyCtxt<'_>, region: Region<'_>) -> bool {
         // ignore it.  We can't put it on the struct header anyway.
         RegionKind::ReLateBound(..) => false,
 
-        // This can appear with malformed code (#64855):
+        // This can appear in `where Self: ` bounds (#64855):
         //
         //     struct Bar<T>(<Self as Foo>::Type) where Self: ;
-        //
-        // We accept it only to avoid an ICE.
-        RegionKind::ReEmpty => {
-            tcx.sess.delay_span_bug(
-                DUMMY_SP,
-                &format!("unexpected region in outlives inference: {:?}", region),
-            );
-            false
-        }
+        //     struct Baz<'a>(&'a Self) where Self: ;
+        RegionKind::ReEmpty => false,
 
         // These regions don't appear in types from type declarations:
         RegionKind::ReErased
diff --git a/src/test/ui/associated-types/issue-64855-2.rs b/src/test/ui/associated-types/issue-64855-2.rs
new file mode 100644
index 0000000000000..1d53bd5703165
--- /dev/null
+++ b/src/test/ui/associated-types/issue-64855-2.rs
@@ -0,0 +1,5 @@
+// check-pass
+
+pub struct Bar<'a>(&'a Self) where Self: ;
+
+fn main() {}