Add basic specialization tests, including for default item

inheritance. Updates some of the coherence tests as well.

15 files changed, 570 insertions, 19 deletions

diff --git a/src/test/auxiliary/go_trait.rs b/src/test/auxiliary/go_trait.rs
index 0a921c8f5b3..ab1051c5650 100644
--- a/src/test/auxiliary/go_trait.rs
+++ b/src/test/auxiliary/go_trait.rs
@@ -37,7 +37,7 @@ pub fn go_once<G:GoOnce>(this: G, arg: isize) {
 impl<G> GoMut for G
     where G : Go
 {
-    fn go_mut(&mut self, arg: isize) {
+    default fn go_mut(&mut self, arg: isize) {
         go(&*self, arg)
     }
 }
@@ -45,7 +45,7 @@ impl<G> GoMut for G
 impl<G> GoOnce for G
     where G : GoMut
 {
-    fn go_once(mut self, arg: isize) {
+    default fn go_once(mut self, arg: isize) {
         go_mut(&mut self, arg)
     }
 }
diff --git a/src/test/auxiliary/specialization_cross_crate.rs b/src/test/auxiliary/specialization_cross_crate.rs
new file mode 100644
index 00000000000..92c985a3e1d
--- /dev/null
+++ b/src/test/auxiliary/specialization_cross_crate.rs
@@ -0,0 +1,80 @@
+// 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 Foo {
+    fn foo(&self) -> &'static str;
+}
+
+impl<T> Foo for T {
+    default fn foo(&self) -> &'static str {
+        "generic"
+    }
+}
+
+impl<T: Clone> Foo for T {
+    default fn foo(&self) -> &'static str {
+        "generic Clone"
+    }
+}
+
+impl<T, U> Foo for (T, U) where T: Clone, U: Clone {
+    default fn foo(&self) -> &'static str {
+        "generic pair"
+    }
+}
+
+impl<T: Clone> Foo for (T, T) {
+    default fn foo(&self) -> &'static str {
+        "generic uniform pair"
+    }
+}
+
+impl Foo for (u8, u32) {
+    default fn foo(&self) -> &'static str {
+        "(u8, u32)"
+    }
+}
+
+impl Foo for (u8, u8) {
+    default fn foo(&self) -> &'static str {
+        "(u8, u8)"
+    }
+}
+
+impl<T: Clone> Foo for Vec<T> {
+    default fn foo(&self) -> &'static str {
+        "generic Vec"
+    }
+}
+
+impl Foo for Vec<i32> {
+    fn foo(&self) -> &'static str {
+        "Vec<i32>"
+    }
+}
+
+impl Foo for String {
+    fn foo(&self) -> &'static str {
+        "String"
+    }
+}
+
+impl Foo for i32 {
+    fn foo(&self) -> &'static str {
+        "i32"
+    }
+}
+
+pub trait MyMarker {}
+impl<T: Clone + MyMarker> Foo for T {
+    default fn foo(&self) -> &'static str {
+        "generic Clone + MyMarker"
+    }
+}
diff --git a/src/test/auxiliary/specialization_cross_crate_defaults.rs b/src/test/auxiliary/specialization_cross_crate_defaults.rs
new file mode 100755
index 00000000000..b62d80b589f
--- /dev/null
+++ b/src/test/auxiliary/specialization_cross_crate_defaults.rs
@@ -0,0 +1,49 @@
+// 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.
+
+
+#![feature(specialization)]
+
+// First, test only use of explicit `default` items:
+
+pub trait Foo {
+    fn foo(&self) -> bool;
+}
+
+impl<T> Foo for T {
+    default fn foo(&self) -> bool { false }
+}
+
+impl Foo for i32 {}
+
+impl Foo for i64 {
+    fn foo(&self) -> bool { true }
+}
+
+// Next, test mixture of explicit `default` and provided methods:
+
+pub trait Bar {
+    fn bar(&self) -> i32 { 0 }
+}
+
+impl<T> Bar for T {} // use the provided method
+
+impl Bar for i32 {
+    fn bar(&self) -> i32 { 1 }
+}
+impl<'a> Bar for &'a str {}
+
+impl<T> Bar for Vec<T> {
+    default fn bar(&self) -> i32 { 2 }
+}
+impl Bar for Vec<i32> {}
+impl Bar for Vec<i64> {
+    fn bar(&self) -> i32 { 3 }
+}
diff --git a/src/test/compile-fail/coherence-no-direct-lifetime-dispatch.rs b/src/test/compile-fail/coherence-no-direct-lifetime-dispatch.rs
new file mode 100644
index 00000000000..6de338f1db0
--- /dev/null
+++ b/src/test/compile-fail/coherence-no-direct-lifetime-dispatch.rs
@@ -0,0 +1,18 @@
+// 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.
+
+// Test that you cannot *directly* dispatch on lifetime requirements
+
+trait MyTrait {}
+
+impl<T> MyTrait for T {}
+impl<T: 'static> MyTrait for T {} //~ ERROR E0119
+
+fn main() {}
diff --git a/src/test/compile-fail/coherence-overlap-messages.rs b/src/test/compile-fail/coherence-overlap-messages.rs
index 4f1092f960e..2a54ad88055 100644
--- a/src/test/compile-fail/coherence-overlap-messages.rs
+++ b/src/test/compile-fail/coherence-overlap-messages.rs
@@ -15,28 +15,18 @@ impl<U> Foo for U {}
 
 trait Bar {}
 
-impl<T> Bar for T {} //~ ERROR conflicting implementations of trait `Bar` for type `u8`:
-impl Bar for u8 {}
+impl<T> Bar for (T, u8) {} //~ ERROR conflicting implementations of trait `Bar` for type `(u8, u8)`:
+impl<T> Bar for (u8, T) {}
 
 trait Baz<T> {}
 
-impl<T, U> Baz<U> for T {} //~ ERROR conflicting implementations of trait `Baz<_>` for type `u8`:
+impl<T> Baz<u8> for T {} //~ ERROR conflicting implementations of trait `Baz<u8>` for type `u8`:
 impl<T> Baz<T> for u8 {}
 
-trait Quux<T> {}
+trait Quux<U, V> {}
 
-impl<T, U> Quux<U> for T {} //~ ERROR conflicting implementations of trait `Quux<_>`:
-impl<T> Quux<T> for T {}
-
-trait Qaar<T> {}
-
-impl<T, U> Qaar<U> for T {} //~ ERROR conflicting implementations of trait `Qaar<u8>`:
-impl<T> Qaar<u8> for T {}
-
-trait Qaax<T> {}
-
-impl<T, U> Qaax<U> for T {}
-//~^ ERROR conflicting implementations of trait `Qaax<u8>` for type `u32`:
-impl Qaax<u8> for u32 {}
+impl<T, U, V> Quux<U, V> for T {} //~ ERROR conflicting implementations of trait `Quux<_, _>`:
+impl<T, U> Quux<U, U> for T {}
+impl<T, V> Quux<T, V> for T {}
 
 fn main() {}
diff --git a/src/test/compile-fail/specialization-negative-impl.rs b/src/test/compile-fail/specialization-negative-impl.rs
new file mode 100644
index 00000000000..d0d698d12e0
--- /dev/null
+++ b/src/test/compile-fail/specialization-negative-impl.rs
@@ -0,0 +1,23 @@
+// 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.
+
+#![feature(optin_builtin_traits)]
+
+struct TestType<T>(T);
+
+unsafe impl<T> Send for TestType<T> {}
+impl !Send for TestType<u8> {}
+
+fn assert_send<T: Send>() {}
+
+fn main() {
+    assert_send::<TestType<()>>();
+    assert_send::<TestType<u8>>(); //~ ERROR
+}
diff --git a/src/test/compile-fail/specialization-overlap-negative.rs b/src/test/compile-fail/specialization-overlap-negative.rs
new file mode 100644
index 00000000000..cc427b4fed2
--- /dev/null
+++ b/src/test/compile-fail/specialization-overlap-negative.rs
@@ -0,0 +1,20 @@
+// 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.
+
+#![feature(optin_builtin_traits)]
+
+trait MyTrait {}
+
+struct TestType<T>(::std::marker::PhantomData<T>);
+
+unsafe impl<T: Clone> Send for TestType<T> {}
+impl<T: MyTrait> !Send for TestType<T> {} //~ ERROR E0119
+
+fn main() {}
diff --git a/src/test/compile-fail/specialization-overlap.rs b/src/test/compile-fail/specialization-overlap.rs
new file mode 100644
index 00000000000..7d14e85fba8
--- /dev/null
+++ b/src/test/compile-fail/specialization-overlap.rs
@@ -0,0 +1,23 @@
+// 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.
+
+trait Foo {}
+impl<T: Clone> Foo for T {}
+impl<T> Foo for Vec<T> {} //~ ERROR E0119
+
+trait Bar {}
+impl<T> Bar for (T, u8) {}
+impl<T> Bar for (u8, T) {} //~ ERROR E0119
+
+trait Baz<U> {}
+impl<T> Baz<T> for u8 {}
+impl<T> Baz<u8> for T {} //~ ERROR E0119
+
+fn main() {}
diff --git a/src/test/run-pass/specialization-allowed-cross-crate.rs b/src/test/run-pass/specialization-allowed-cross-crate.rs
new file mode 100644
index 00000000000..139c63d3cdb
--- /dev/null
+++ b/src/test/run-pass/specialization-allowed-cross-crate.rs
@@ -0,0 +1,29 @@
+// 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.
+
+// aux-build:go_trait.rs
+
+extern crate go_trait;
+
+use go_trait::{Go,GoMut};
+use std::fmt::Debug;
+use std::default::Default;
+
+struct MyThingy;
+
+impl Go for MyThingy {
+    fn go(&self, arg: isize) { }
+}
+
+impl GoMut for MyThingy {
+    fn go_mut(&mut self, arg: isize) { }
+}
+
+fn main() { }
diff --git a/src/test/run-pass/specialization-assoc-fns.rs b/src/test/run-pass/specialization-assoc-fns.rs
new file mode 100644
index 00000000000..750581ffe92
--- /dev/null
+++ b/src/test/run-pass/specialization-assoc-fns.rs
@@ -0,0 +1,33 @@
+// 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.
+
+trait Foo {
+    fn mk() -> Self;
+}
+
+impl<T: Default> Foo for T {
+    default fn mk() -> T {
+        T::default()
+    }
+}
+
+impl Foo for Vec<u8> {
+    fn mk() -> Vec<u8> {
+        vec![0]
+    }
+}
+
+fn main() {
+    let v1: Vec<i32> = Foo::mk();
+    let v2: Vec<u8> = Foo::mk();
+
+    assert!(v1.len() == 0);
+    assert!(v2.len() == 1);
+}
diff --git a/src/test/run-pass/specialization-basics.rs b/src/test/run-pass/specialization-basics.rs
new file mode 100644
index 00000000000..e585c8e2353
--- /dev/null
+++ b/src/test/run-pass/specialization-basics.rs
@@ -0,0 +1,104 @@
+// 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.
+
+// Tests a variety of basic specialization scenarios and method
+// dispatch for them.
+
+trait Foo {
+    fn foo(&self) -> &'static str;
+}
+
+impl<T> Foo for T {
+    default fn foo(&self) -> &'static str {
+        "generic"
+    }
+}
+
+impl<T: Clone> Foo for T {
+    default fn foo(&self) -> &'static str {
+        "generic Clone"
+    }
+}
+
+impl<T, U> Foo for (T, U) where T: Clone, U: Clone {
+    default fn foo(&self) -> &'static str {
+        "generic pair"
+    }
+}
+
+impl<T: Clone> Foo for (T, T) {
+    default fn foo(&self) -> &'static str {
+        "generic uniform pair"
+    }
+}
+
+impl Foo for (u8, u32) {
+    default fn foo(&self) -> &'static str {
+        "(u8, u32)"
+    }
+}
+
+impl Foo for (u8, u8) {
+    default fn foo(&self) -> &'static str {
+        "(u8, u8)"
+    }
+}
+
+impl<T: Clone> Foo for Vec<T> {
+    default fn foo(&self) -> &'static str {
+        "generic Vec"
+    }
+}
+
+impl Foo for Vec<i32> {
+    fn foo(&self) -> &'static str {
+        "Vec<i32>"
+    }
+}
+
+impl Foo for String {
+    fn foo(&self) -> &'static str {
+        "String"
+    }
+}
+
+impl Foo for i32 {
+    fn foo(&self) -> &'static str {
+        "i32"
+    }
+}
+
+struct NotClone;
+
+trait MyMarker {}
+impl<T: Clone + MyMarker> Foo for T {
+    default fn foo(&self) -> &'static str {
+        "generic Clone + MyMarker"
+    }
+}
+
+#[derive(Clone)]
+struct MarkedAndClone;
+impl MyMarker for MarkedAndClone {}
+
+fn  main() {
+    assert!(NotClone.foo() == "generic");
+    assert!(0u8.foo() == "generic Clone");
+    assert!(vec![NotClone].foo() == "generic");
+    assert!(vec![0u8].foo() == "generic Vec");
+    assert!(vec![0i32].foo() == "Vec<i32>");
+    assert!(0i32.foo() == "i32");
+    assert!(String::new().foo() == "String");
+    assert!(((), 0).foo() == "generic pair");
+    assert!(((), ()).foo() == "generic uniform pair");
+    assert!((0u8, 0u32).foo() == "(u8, u32)");
+    assert!((0u8, 0u8).foo() == "(u8, u8)");
+    assert!(MarkedAndClone.foo() == "generic Clone + MyMarker");
+}
diff --git a/src/test/run-pass/specialization-cross-crate-defaults.rs b/src/test/run-pass/specialization-cross-crate-defaults.rs
new file mode 100644
index 00000000000..750c3cf8b3e
--- /dev/null
+++ b/src/test/run-pass/specialization-cross-crate-defaults.rs
@@ -0,0 +1,37 @@
+// 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.
+
+// aux-build:specialization_cross_crate_defaults.rs
+
+#![feature(specialization)]
+
+extern crate specialization_cross_crate_defaults;
+
+use specialization_cross_crate_defaults::*;
+
+fn test_foo() {
+    assert!(0i8.foo() == false);
+    assert!(0i32.foo() == false);
+    assert!(0i64.foo() == true);
+}
+
+fn test_bar() {
+    assert!(0u8.bar() == 0);
+    assert!(0i32.bar() == 1);
+    assert!("hello".bar() == 0);
+    assert!(vec![()].bar() == 2);
+    assert!(vec![0i32].bar() == 2);
+    assert!(vec![0i64].bar() == 3);
+}
+
+fn main() {
+    test_foo();
+    test_bar();
+}
diff --git a/src/test/run-pass/specialization-cross-crate.rs b/src/test/run-pass/specialization-cross-crate.rs
new file mode 100644
index 00000000000..c74b1f2e49e
--- /dev/null
+++ b/src/test/run-pass/specialization-cross-crate.rs
@@ -0,0 +1,56 @@
+// 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.
+
+// aux-build:specialization_cross_crate.rs
+
+extern crate specialization_cross_crate;
+
+use specialization_cross_crate::*;
+
+struct NotClone;
+
+#[derive(Clone)]
+struct MarkedAndClone;
+impl MyMarker for MarkedAndClone {}
+
+struct MyType<T>(T);
+impl<T> Foo for MyType<T> {
+    default fn foo(&self) -> &'static str {
+        "generic MyType"
+    }
+}
+
+impl Foo for MyType<u8> {
+    fn foo(&self) -> &'static str {
+        "MyType<u8>"
+    }
+}
+
+struct MyOtherType;
+impl Foo for MyOtherType {}
+
+fn  main() {
+    assert!(NotClone.foo() == "generic");
+    assert!(0u8.foo() == "generic Clone");
+    assert!(vec![NotClone].foo() == "generic");
+    assert!(vec![0u8].foo() == "generic Vec");
+    assert!(vec![0i32].foo() == "Vec<i32>");
+    assert!(0i32.foo() == "i32");
+    assert!(String::new().foo() == "String");
+    assert!(((), 0).foo() == "generic pair");
+    assert!(((), ()).foo() == "generic uniform pair");
+    assert!((0u8, 0u32).foo() == "(u8, u32)");
+    assert!((0u8, 0u8).foo() == "(u8, u8)");
+    assert!(MarkedAndClone.foo() == "generic Clone + MyMarker");
+
+    assert!(MyType(()).foo() == "generic MyType");
+    assert!(MyType(0u8).foo() == "MyType<u8>");
+    assert!(MyOtherType.foo() == "generic");
+}
diff --git a/src/test/run-pass/specialization-default-methods.rs b/src/test/run-pass/specialization-default-methods.rs
new file mode 100644
index 00000000000..7482d3acbc1
--- /dev/null
+++ b/src/test/run-pass/specialization-default-methods.rs
@@ -0,0 +1,66 @@
+// 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.
+
+// First, test only use of explicit `default` items:
+
+trait Foo {
+    fn foo(&self) -> bool;
+}
+
+impl<T> Foo for T {
+    default fn foo(&self) -> bool { false }
+}
+
+impl Foo for i32 {}
+
+impl Foo for i64 {
+    fn foo(&self) -> bool { true }
+}
+
+fn test_foo() {
+    assert!(0i8.foo() == false);
+    assert!(0i32.foo() == false);
+    assert!(0i64.foo() == true);
+}
+
+// Next, test mixture of explicit `default` and provided methods:
+
+trait Bar {
+    fn bar(&self) -> i32 { 0 }
+}
+
+impl<T> Bar for T {} // use the provided method
+
+impl Bar for i32 {
+    fn bar(&self) -> i32 { 1 }
+}
+impl<'a> Bar for &'a str {}
+
+impl<T> Bar for Vec<T> {
+    default fn bar(&self) -> i32 { 2 }
+}
+impl Bar for Vec<i32> {}
+impl Bar for Vec<i64> {
+    fn bar(&self) -> i32 { 3 }
+}
+
+fn test_bar() {
+    assert!(0u8.bar() == 0);
+    assert!(0i32.bar() == 1);
+    assert!("hello".bar() == 0);
+    assert!(vec![()].bar() == 2);
+    assert!(vec![0i32].bar() == 2);
+    assert!(vec![0i64].bar() == 3);
+}
+
+fn main() {
+    test_foo();
+    test_bar();
+}
diff --git a/src/test/run-pass/specialization-super-traits.rs b/src/test/run-pass/specialization-super-traits.rs
new file mode 100644
index 00000000000..4a30e6bcd25
--- /dev/null
+++ b/src/test/run-pass/specialization-super-traits.rs
@@ -0,0 +1,23 @@
+// 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.
+
+// Test that you can specialize via an explicit trait hierarchy
+
+// FIXME: this doesn't work yet...
+
+trait Parent {}
+trait Child: Parent {}
+
+trait Foo {}
+
+impl<T: Parent> Foo for T {}
+impl<T: Child> Foo for T {}
+
+fn main() {}