Auto merge of #51096 - matthewjasper:reverse-normalization-bounds, r=nikomatsakis

Register outlives predicates from queries the right way around.

Closes #49354
The region constraints from queries need to be reversed from sub to outlives.

Note: wf checking reports these errors before NLL, so I'm not sure if there's any case when these predicates need to be created at all.

cc @nikomatsakis

src/librustc_traits/util.rs

@@ -74,17 +74,19 @@ where
         let mut outlives: Vec<_> = constraints
             .into_iter()
             .map(|(k, _)| match *k {
+                // Swap regions because we are going from sub (<=) to outlives
+                // (>=).
                 Constraint::VarSubVar(v1, v2) => ty::OutlivesPredicate(
-                    tcx.mk_region(ty::ReVar(v1)).into(),
-                    tcx.mk_region(ty::ReVar(v2)),
+                    tcx.mk_region(ty::ReVar(v2)).into(),
+                    tcx.mk_region(ty::ReVar(v1)),
                 ),
                 Constraint::VarSubReg(v1, r2) => {
-                    ty::OutlivesPredicate(tcx.mk_region(ty::ReVar(v1)).into(), r2)
+                    ty::OutlivesPredicate(r2.into(), tcx.mk_region(ty::ReVar(v1)))
                 }
                 Constraint::RegSubVar(r1, v2) => {
-                    ty::OutlivesPredicate(r1.into(), tcx.mk_region(ty::ReVar(v2)))
+                    ty::OutlivesPredicate(tcx.mk_region(ty::ReVar(v2)).into(), r1)
                 }
-                Constraint::RegSubReg(r1, r2) => ty::OutlivesPredicate(r1.into(), r2),
+                Constraint::RegSubReg(r1, r2) => ty::OutlivesPredicate(r2.into(), r1),
             })
             .map(ty::Binder::dummy) // no bound regions in the code above
             .collect();

src/test/ui/nll/normalization-bounds-error.rs

@@ -0,0 +1,26 @@
+// 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.
+
+// Check that we error when a bound from the impl is not satisfied when
+// normalizing an associated type.
+
+#![feature(nll)]
+trait Visitor<'d> {
+    type Value;
+}
+
+impl<'a, 'd: 'a> Visitor<'d> for &'a () {
+    type Value = ();
+}
+
+fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
+//~^ ERROR
+
+fn main() {}

src/test/ui/nll/normalization-bounds-error.stderr

@@ -0,0 +1,23 @@
+error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'d` due to conflicting requirements
+  --> $DIR/normalization-bounds-error.rs:23:1
+   |
+LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: first, the lifetime cannot outlive the lifetime 'd as defined on the function body at 23:1...
+  --> $DIR/normalization-bounds-error.rs:23:1
+   |
+LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: ...but the lifetime must also be valid for the lifetime 'a as defined on the function body at 23:1...
+  --> $DIR/normalization-bounds-error.rs:23:1
+   |
+LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: ...so that the types are compatible:
+           expected Visitor<'d>
+              found Visitor<'_>
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/normalization-bounds.rs

@@ -0,0 +1,26 @@
+// 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.
+
+// Check that lifetime bounds get checked the right way around with NLL enabled.
+
+//run-pass
+
+#![feature(nll)]
+trait Visitor<'d> {
+    type Value;
+}
+
+impl<'a, 'd: 'a> Visitor<'d> for &'a () {
+    type Value = ();
+}
+
+fn visit_seq<'d: 'a, 'a>() -> <&'a () as Visitor<'d>>::Value {}
+
+fn main() {}