Auto merge of #44691 - cramertj:underscore-lifetimes, r=nikomatsakis

Implement underscore lifetimes

Part of https://github.com/rust-lang/rust/issues/44524

src/test/compile-fail/E0637.rs

@@ -0,0 +1,20 @@
+// 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(underscore_lifetimes)]
+
+struct Foo<'a: '_>(&'a u8); //~ ERROR invalid lifetime bound name: `'_`
+fn foo<'a: '_>(_: &'a u8) {} //~ ERROR invalid lifetime bound name: `'_`
+
+struct Bar<'a>(&'a u8);
+impl<'a: '_> Bar<'a> { //~ ERROR invalid lifetime bound name: `'_`
+  fn bar() {}
+}
+
+fn main() {}

src/test/compile-fail/feature-gate-underscore-lifetimes.rs

@@ -0,0 +1,20 @@
+// 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.
+
+struct Foo<'a>(&'a u8);
+
+fn foo(x: &u8) -> Foo<'_> { //~ ERROR underscore lifetimes are unstable
+    Foo(x)
+}
+
+fn main() {
+    let x = 5;
+    let _ = foo(&x);
+}

src/test/compile-fail/label-underscore.rs

@@ -8,12 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn _f<'_>() //~ ERROR invalid lifetime name `'_`
-    -> &'_ u8 //~ ERROR invalid lifetime name `'_`
-{
-    panic!();
-}
-
 fn main() {
     '_: loop { //~ ERROR invalid label name `'_`
         break '_ //~ ERROR invalid label name `'_`

src/test/compile-fail/underscore-lifetime-binders.rs

@@ -0,0 +1,39 @@
+// 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(underscore_lifetimes)]
+
+struct Foo<'a>(&'a u8);
+struct Baz<'a>(&'_ &'a u8); //~ ERROR missing lifetime specifier
+
+impl Foo<'_> { //~ ERROR missing lifetime specifier
+    fn x() {}
+}
+
+fn foo<'_> //~ ERROR invalid lifetime parameter name: `'_`
+(_: Foo<'_>) {}
+
+trait Meh<'a> {}
+impl<'a> Meh<'a> for u8 {}
+
+fn meh() -> Box<for<'_> Meh<'_>> //~ ERROR invalid lifetime parameter name: `'_`
+//~^ ERROR missing lifetime specifier
+//~^^ ERROR missing lifetime specifier
+{
+  Box::new(5u8)
+}
+
+fn foo2(_: &'_ u8, y: &'_ u8) -> &'_ u8 { y } //~ ERROR missing lifetime specifier
+
+fn main() {
+    let x = 5;
+    foo(Foo(&x));
+    let _ = meh();
+}

src/test/compile-fail/underscore-lifetime-elison-mismatch.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(underscore_lifetimes)]
+
+fn foo(x: &mut Vec<&'_ u8>, y: &'_ u8) { x.push(y); } //~ ERROR lifetime mismatch
+
+fn main() {}

src/test/run-pass/underscore-lifetimes.rs

@@ -0,0 +1,47 @@
+// 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(underscore_lifetimes)]
+
+struct Foo<'a>(&'a u8);
+
+fn foo(x: &u8) -> Foo<'_> {
+    Foo(x)
+}
+
+fn foo2(x: &'_ u8) -> Foo<'_> {
+    Foo(x)
+}
+
+fn foo3(x: &'_ u8) -> Foo {
+    Foo(x)
+}
+
+fn foo4(_: Foo<'_>) {}
+
+struct Foo2<'a, 'b> {
+    a: &'a u8,
+    b: &'b u8,
+}
+fn foo5<'b>(foo: Foo2<'_, 'b>) -> &'b u8 {
+    foo.b
+}
+
+fn main() {
+    let x = &5;
+    let _ = foo(x);
+    let _ = foo2(x);
+    let _ = foo3(x);
+    foo4(Foo(x));
+    let _ = foo5(Foo2 {
+        a: x,
+        b: &6,
+    });
+}