Auto merge of #39158 - petrochenkov:bounds, r=nikomatsakis

Bounds parsing refactoring 2

See https://github.com/rust-lang/rust/pull/37511 for previous discussion.
cc @matklad

Relaxed parsing rules:
 - zero bounds after `:` are allowed in all contexts.
 - zero predicates are allowed after `where`.
- trailing separator `,` is allowed after predicates in `where` clauses not followed by `{`.

Other parsing rules:
 - trailing separator `+` is still allowed in all bound lists.

Code is also cleaned up and tests added.

I haven't touched parsing of trait object types yet, I'll do it later.

27 files changed, 233 insertions, 30 deletions

diff --git a/src/test/compile-fail/attrs-with-no-formal-in-generics-2.rs b/src/test/compile-fail/attrs-with-no-formal-in-generics-2.rs
index a38a7bfb937..5e09473ab77 100644
--- a/src/test/compile-fail/attrs-with-no-formal-in-generics-2.rs
+++ b/src/test/compile-fail/attrs-with-no-formal-in-generics-2.rs
@@ -17,10 +17,7 @@
 
 struct RefAny<'a, T>(&'a T);
 
-impl<#[rustc_1] 'a, #[rustc_2] T, #[oops]> RefAny<'a, T> {
-    //~^ ERROR expected identifier, found `>`
-}
+impl<#[rustc_1] 'a, #[rustc_2] T, #[oops]> RefAny<'a, T> {}
+//~^ ERROR trailing attribute after type parameters
 
-fn main() {
-
-}
+fn main() {}
diff --git a/src/test/compile-fail/generic-non-trailing-defaults.rs b/src/test/compile-fail/generic-non-trailing-defaults.rs
new file mode 100644
index 00000000000..77e55203263
--- /dev/null
+++ b/src/test/compile-fail/generic-non-trailing-defaults.rs
@@ -0,0 +1,20 @@
+// Copyright 2014 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.
+
+struct Heap;
+
+struct Vec<A = Heap, T>;
+//~^ ERROR type parameters with a default must be trailing
+
+struct Foo<A, B = Vec<C>, C>;
+//~^ ERROR type parameters with a default must be trailing
+//~| ERROR type parameters with a default cannot use forward declared identifiers
+
+fn main() {}
diff --git a/src/test/compile-fail/impl-trait/no-trait.rs b/src/test/compile-fail/impl-trait/no-trait.rs
new file mode 100644
index 00000000000..ce61c5bf63d
--- /dev/null
+++ b/src/test/compile-fail/impl-trait/no-trait.rs
@@ -0,0 +1,15 @@
+// Copyright 2017 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(conservative_impl_trait)]
+
+fn f() -> impl 'static {} //~ ERROR at least one trait must be specified
+
+fn main() {}
diff --git a/src/test/compile-fail/issue-20616-1.rs b/src/test/compile-fail/issue-20616-1.rs
index 5b4f9942d28..a1949df661a 100644
--- a/src/test/compile-fail/issue-20616-1.rs
+++ b/src/test/compile-fail/issue-20616-1.rs
@@ -16,7 +16,7 @@
 type Type_1_<'a, T> = &'a T;
 
 
-type Type_1<'a T> = &'a T; //~ error: expected `,` or `>` after lifetime name, found `T`
+type Type_1<'a T> = &'a T; //~ error: expected one of `,`, `:`, or `>`, found `T`
 
 
 //type Type_2 = Type_1_<'static ()>; // error: expected `,` or `>` after lifetime name, found `(`
diff --git a/src/test/compile-fail/issue-20616-2.rs b/src/test/compile-fail/issue-20616-2.rs
index 65305ff3ac8..87b836d6872 100644
--- a/src/test/compile-fail/issue-20616-2.rs
+++ b/src/test/compile-fail/issue-20616-2.rs
@@ -19,7 +19,7 @@ type Type_1_<'a, T> = &'a T;
 //type Type_1<'a T> = &'a T; // error: expected `,` or `>` after lifetime name, found `T`
 
 
-type Type_2 = Type_1_<'static ()>; //~ error: expected `,` or `>` after lifetime name, found `(`
+type Type_2 = Type_1_<'static ()>; //~ error: expected one of `,` or `>`, found `(`
 
 
 //type Type_3<T> = Box<T,,>; // error: expected type, found `,`
diff --git a/src/test/compile-fail/issue-20616-3.rs b/src/test/compile-fail/issue-20616-3.rs
index 101f81019d9..e5ed46d2cb3 100644
--- a/src/test/compile-fail/issue-20616-3.rs
+++ b/src/test/compile-fail/issue-20616-3.rs
@@ -22,7 +22,7 @@ type Type_1_<'a, T> = &'a T;
 //type Type_2 = Type_1_<'static ()>; // error: expected `,` or `>` after lifetime name, found `(`
 
 
-type Type_3<T> = Box<T,,>; //~ error: expected type, found `,`
+type Type_3<T> = Box<T,,>; //~ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_4<T> = Type_1_<'static,, T>; // error: expected type, found `,`
diff --git a/src/test/compile-fail/issue-20616-4.rs b/src/test/compile-fail/issue-20616-4.rs
index 6450e9ed68c..9b731289e13 100644
--- a/src/test/compile-fail/issue-20616-4.rs
+++ b/src/test/compile-fail/issue-20616-4.rs
@@ -25,7 +25,8 @@ type Type_1_<'a, T> = &'a T;
 //type Type_3<T> = Box<T,,>; // error: expected type, found `,`
 
 
-type Type_4<T> = Type_1_<'static,, T>; //~ error: expected type, found `,`
+type Type_4<T> = Type_1_<'static,, T>;
+//~^ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 type Type_5_<'a> = Type_1_<'a, ()>;
diff --git a/src/test/compile-fail/issue-20616-5.rs b/src/test/compile-fail/issue-20616-5.rs
index d1840427ad8..5e3b024da9a 100644
--- a/src/test/compile-fail/issue-20616-5.rs
+++ b/src/test/compile-fail/issue-20616-5.rs
@@ -31,7 +31,8 @@ type Type_1_<'a, T> = &'a T;
 type Type_5_<'a> = Type_1_<'a, ()>;
 
 
-type Type_5<'a> = Type_1_<'a, (),,>; //~ error: expected type, found `,`
+type Type_5<'a> = Type_1_<'a, (),,>;
+//~^ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_6 = Type_5_<'a,,>; // error: expected type, found `,`
diff --git a/src/test/compile-fail/issue-20616-6.rs b/src/test/compile-fail/issue-20616-6.rs
index b0b5bc653f6..b6ee26f9f62 100644
--- a/src/test/compile-fail/issue-20616-6.rs
+++ b/src/test/compile-fail/issue-20616-6.rs
@@ -34,7 +34,8 @@ type Type_5_<'a> = Type_1_<'a, ()>;
 //type Type_5<'a> = Type_1_<'a, (),,>; // error: expected type, found `,`
 
 
-type Type_6 = Type_5_<'a,,>; //~ error: expected type, found `,`
+type Type_6 = Type_5_<'a,,>;
+//~^ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_7 = Box<(),,>; // error: expected type, found `,`
diff --git a/src/test/compile-fail/issue-20616-7.rs b/src/test/compile-fail/issue-20616-7.rs
index 0958f8b4ed2..fef3dd4e31d 100644
--- a/src/test/compile-fail/issue-20616-7.rs
+++ b/src/test/compile-fail/issue-20616-7.rs
@@ -37,7 +37,7 @@ type Type_5_<'a> = Type_1_<'a, ()>;
 //type Type_6 = Type_5_<'a,,>; // error: expected type, found `,`
 
 
-type Type_7 = Box<(),,>; //~ error: expected type, found `,`
+type Type_7 = Box<(),,>; //~ error: expected one of `>`, identifier, lifetime, or type, found `,`
 
 
 //type Type_8<'a,,> = &'a (); // error: expected ident, found `,`
diff --git a/src/test/compile-fail/issue-20616-8.rs b/src/test/compile-fail/issue-20616-8.rs
index d6cf9acae9b..b7bef47c4f4 100644
--- a/src/test/compile-fail/issue-20616-8.rs
+++ b/src/test/compile-fail/issue-20616-8.rs
@@ -40,7 +40,7 @@ type Type_5_<'a> = Type_1_<'a, ()>;
 //type Type_7 = Box<(),,>; // error: expected type, found `,`
 
 
-type Type_8<'a,,> = &'a (); //~ error: expected identifier, found `,`
+type Type_8<'a,,> = &'a (); //~ error: expected one of `>`, identifier, or lifetime, found `,`
 
 
 //type Type_9<T,,> = Box<T>; // error: expected identifier, found `,`
diff --git a/src/test/compile-fail/issue-20616-9.rs b/src/test/compile-fail/issue-20616-9.rs
index d64cec446ef..5c16d24cef8 100644
--- a/src/test/compile-fail/issue-20616-9.rs
+++ b/src/test/compile-fail/issue-20616-9.rs
@@ -43,4 +43,4 @@ type Type_5_<'a> = Type_1_<'a, ()>;
 //type Type_8<'a,,> = &'a (); // error: expected identifier, found `,`
 
 
-type Type_9<T,,> = Box<T>; //~ error: expected identifier, found `,`
+type Type_9<T,,> = Box<T>; //~ error: expected one of `>`, identifier, or lifetime, found `,`
diff --git a/src/test/compile-fail/where-equality-constraints.rs b/src/test/compile-fail/where-equality-constraints.rs
new file mode 100644
index 00000000000..5b2fe2901c4
--- /dev/null
+++ b/src/test/compile-fail/where-equality-constraints.rs
@@ -0,0 +1,16 @@
+// Copyright 2017 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.
+
+fn f() where u8 = u16 {}
+//~^ ERROR equality constraints are not yet supported in where clauses
+fn g() where for<'a> &(u8,) == u16, {}
+//~^ ERROR equality constraints are not yet supported in where clauses
+
+fn main() {}
diff --git a/src/test/compile-fail/where-lifetime-resolution.rs b/src/test/compile-fail/where-lifetime-resolution.rs
new file mode 100644
index 00000000000..f4c6842206d
--- /dev/null
+++ b/src/test/compile-fail/where-lifetime-resolution.rs
@@ -0,0 +1,23 @@
+// Copyright 2017 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.
+
+trait Trait1 {}
+trait Trait2 {}
+
+fn f() where
+    for<'a> Trait1<'a>: Trait1<'a>, // OK
+    (for<'a> Trait1<'a>): Trait1<'a>,
+    //~^ ERROR use of undeclared lifetime name `'a`
+    for<'a> for<'b> Trait2<'a, 'b>: Trait2<'a, 'b>,
+    //~^ ERROR use of undeclared lifetime name `'b`
+    //~| ERROR nested quantification of lifetimes
+{}
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-lifetime-1.rs b/src/test/parse-fail/bounds-lifetime-1.rs
new file mode 100644
index 00000000000..824d243d5f8
--- /dev/null
+++ b/src/test/parse-fail/bounds-lifetime-1.rs
@@ -0,0 +1,15 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+type A = for<'a 'b> fn(); //~ ERROR expected one of `,`, `:`, or `>`, found `'b`
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-lifetime-2.rs b/src/test/parse-fail/bounds-lifetime-2.rs
new file mode 100644
index 00000000000..3c67dda70f5
--- /dev/null
+++ b/src/test/parse-fail/bounds-lifetime-2.rs
@@ -0,0 +1,15 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+type A = for<'a + 'b> fn(); //~ ERROR expected one of `,`, `:`, or `>`, found `+`
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-lifetime-where-1.rs b/src/test/parse-fail/bounds-lifetime-where-1.rs
new file mode 100644
index 00000000000..aae9d729987
--- /dev/null
+++ b/src/test/parse-fail/bounds-lifetime-where-1.rs
@@ -0,0 +1,15 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+type A where 'a; //~ ERROR expected `:`, found `;`
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-lifetime-where.rs b/src/test/parse-fail/bounds-lifetime-where.rs
new file mode 100644
index 00000000000..0a30818bc96
--- /dev/null
+++ b/src/test/parse-fail/bounds-lifetime-where.rs
@@ -0,0 +1,22 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+type A where 'a: 'b + 'c = u8; // OK
+type A where 'a: 'b, = u8; // OK
+type A where 'a: = u8; // OK
+type A where 'a:, = u8; // OK
+type A where 'a: 'b + 'c = u8; // OK
+type A where = u8; // OK
+type A where 'a: 'b + = u8; // OK
+type A where , = u8; //~ ERROR expected one of `=`, lifetime, or type, found `,`
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-lifetime.rs b/src/test/parse-fail/bounds-lifetime.rs
new file mode 100644
index 00000000000..5113a6b4803
--- /dev/null
+++ b/src/test/parse-fail/bounds-lifetime.rs
@@ -0,0 +1,24 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only -Z continue-parse-after-error
+
+type A = for<'a: 'b + 'c> fn(); // OK
+type A = for<'a: 'b,> fn(); // OK
+type A = for<'a:> fn(); // OK
+type A = for<'a:,> fn(); // OK
+type A = for<'a> fn(); // OK
+type A = for<> fn(); // OK
+type A = for<'a: 'b +> fn(); // OK
+
+type A = for<'a, T> fn(); //~ ERROR only lifetime parameters can be used in this context
+type A = for<,> fn(); //~ ERROR expected one of `>`, identifier, or lifetime, found `,`
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-type-where.rs b/src/test/parse-fail/bounds-type-where.rs
new file mode 100644
index 00000000000..9dc5d827744
--- /dev/null
+++ b/src/test/parse-fail/bounds-type-where.rs
@@ -0,0 +1,23 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only
+
+type A where for<'a> for<'b> Trait1 + ?Trait2: 'a + Trait = u8; // OK
+type A where T: Trait, = u8; // OK
+type A where T: = u8; // OK
+type A where T:, = u8; // OK
+type A where T: Trait + Trait = u8; // OK
+type A where = u8; // OK
+type A where T: Trait + = u8; // OK
+type A where T, = u8;
+//~^ ERROR expected one of `!`, `(`, `+`, `::`, `:`, `<`, `==`, or `=`, found `,`
+
+fn main() {}
diff --git a/src/test/parse-fail/bounds-type.rs b/src/test/parse-fail/bounds-type.rs
new file mode 100644
index 00000000000..c224b44a14b
--- /dev/null
+++ b/src/test/parse-fail/bounds-type.rs
@@ -0,0 +1,23 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z parse-only -Z continue-parse-after-error
+
+struct S<
+    T: 'a + Tr, // OK
+    T: Tr + 'a, // OK
+    T: 'a, // OK
+    T:, // OK
+    T: ?for<'a: 'b + 'c> Trait, // OK
+    T: Tr +, // OK
+    T: ?'a, //~ ERROR `?` may only modify trait bounds, not lifetime bounds
+>;
+
+fn main() {}
diff --git a/src/test/parse-fail/issue-14303-path.rs b/src/test/parse-fail/issue-14303-path.rs
index 431a917c2d9..f0d1feffec8 100644
--- a/src/test/parse-fail/issue-14303-path.rs
+++ b/src/test/parse-fail/issue-14303-path.rs
@@ -12,4 +12,3 @@
 
 fn bar<'a, T>(x: mymodule::X<'a, T, 'b, 'c>) {}
 //~^ ERROR lifetime parameters must be declared prior to type parameters
-//~^^ ERROR expected pattern, found `'c`
diff --git a/src/test/parse-fail/generic-non-trailing-defaults.rs b/src/test/parse-fail/issue-17904-2.rs
index 2bb593258ae..3f41c0edd2e 100644
--- a/src/test/parse-fail/generic-non-trailing-defaults.rs
+++ b/src/test/parse-fail/issue-17904-2.rs
@@ -10,10 +10,6 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
-struct Heap;
-
-struct Vec<A = Heap, T>; //~ ERROR type parameters with a default must be trailing
-
-struct Foo<A, B = Vec<C>, C>; //~ ERROR type parameters with a default must be trailing
+struct Bar<T> { x: T } where T: Copy //~ ERROR expected item, found `where`
 
 fn main() {}
diff --git a/src/test/parse-fail/issue-17904.rs b/src/test/parse-fail/issue-17904.rs
index de5aeb02ab7..ae28ac76acb 100644
--- a/src/test/parse-fail/issue-17904.rs
+++ b/src/test/parse-fail/issue-17904.rs
@@ -13,7 +13,6 @@
 struct Baz<U> where U: Eq(U); //This is parsed as the new Fn* style parenthesis syntax.
 struct Baz<U> where U: Eq(U) -> R; // Notice this parses as well.
 struct Baz<U>(U) where U: Eq; // This rightfully signals no error as well.
-struct Foo<T> where T: Copy, (T); //~ ERROR unexpected token in `where` clause
-struct Bar<T> { x: T } where T: Copy //~ ERROR expected item, found `where`
+struct Foo<T> where T: Copy, (T); //~ ERROR expected one of `+`, `:`, `==`, or `=`, found `;`
 
 fn main() {}
diff --git a/src/test/parse-fail/issue-32214.rs b/src/test/parse-fail/issue-32214.rs
index 3ba59c8ee94..9e200094093 100644
--- a/src/test/parse-fail/issue-32214.rs
+++ b/src/test/parse-fail/issue-32214.rs
@@ -10,8 +10,7 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
-pub fn test<W, I: Iterator<Item=(), W> >() {
-    //~^ ERROR expected `=`, found `>`
-}
+pub fn test<W, I: Iterator<Item=(), W> >() {}
+//~^ ERROR type parameters must be declared prior to associated type bindings
 
 fn main() { }
diff --git a/src/test/parse-fail/lifetime-semicolon.rs b/src/test/parse-fail/lifetime-semicolon.rs
index 7010d0e7deb..e1975952fca 100644
--- a/src/test/parse-fail/lifetime-semicolon.rs
+++ b/src/test/parse-fail/lifetime-semicolon.rs
@@ -15,5 +15,4 @@ struct Foo<'a, 'b> {
 }
 
 fn foo<'a, 'b>(x: &mut Foo<'a; 'b>) {}
-//~^ ERROR expected `,` or `>` after lifetime name, found `;`
-//~^^ NOTE did you mean a single argument type &'a Type, or did you mean the comma-separated
+//~^ ERROR expected one of `,` or `>`, found `;`
diff --git a/src/test/parse-fail/where-clauses-no-bounds-or-predicates.rs b/src/test/parse-fail/where-clauses-no-bounds-or-predicates.rs
index 78d97454087..cf67b518fff 100644
--- a/src/test/parse-fail/where-clauses-no-bounds-or-predicates.rs
+++ b/src/test/parse-fail/where-clauses-no-bounds-or-predicates.rs
@@ -10,13 +10,13 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
+// Empty predicate list is OK
 fn equal1<T>(_: &T, _: &T) -> bool where {
-//~^ ERROR a `where` clause must have at least one predicate in it
     true
 }
 
+// Empty bound list is OK
 fn equal2<T>(_: &T, _: &T) -> bool where T: {
-//~^ ERROR each predicate in a `where` clause must have at least one bound
     true
 }