Auto merge of #27045 - nikomatsakis:better-object-defaults-error, r=pnkfelix

Transition to the new object lifetime defaults, replacing the old defaults completely.

r? @pnkfelix 

This is a [breaking-change] as specified by [RFC 1156][1156] (though all cases that would break should have been receiving warnings starting in Rust 1.2). Types like `&'a Box<Trait>` (or `&'a Rc<Trait>`, etc) will change from being interpreted as `&'a Box<Trait+'a>` to `&'a Box<Trait+'static>`. To restore the old behavior, write the `+'a` explicitly. For example, the function:


```rust
trait Trait { }
fn foo(x: &Box<Trait>) { ... }
```

would be rewritten as:

```rust
trait Trait { }
fn foo(x: &'a Box<Trait+'a>) { ... }
```

if one wanted to preserve the current typing.

[1156]: https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md

src/test/compile-fail/lifetime-bound-will-change-warning.rs

@@ -10,8 +10,8 @@
 
 // aux-build:lifetime_bound_will_change_warning_lib.rs
 
-// Test that we get suitable warnings when lifetime bound change will
-// cause breakage.
+// Test that various corner cases cause an error. These are tests
+// that used to pass before we tweaked object defaults.
 
 #![allow(dead_code)]
 #![allow(unused_variables)]
@@ -41,12 +41,12 @@ fn test1cc<'a>(x: &'a Box<Fn()+'a>) {
 
 fn test2<'a>(x: &'a Box<Fn()+'a>) {
     // but ref_obj will not, so warn.
-    ref_obj(x) //~ WARNING this code may fail to compile in Rust 1.3
+    ref_obj(x) //~ ERROR mismatched types
 }
 
 fn test2cc<'a>(x: &'a Box<Fn()+'a>) {
     // same as test2, but cross crate
-    lib::ref_obj(x) //~ WARNING this code may fail to compile in Rust 1.3
+    lib::ref_obj(x) //~ ERROR mismatched types
 }
 
 fn test3<'a>(x: &'a Box<Fn()+'static>) {
@@ -60,5 +60,5 @@ fn test3cc<'a>(x: &'a Box<Fn()+'static>) {
 }
 
 #[rustc_error]
-fn main() { //~ ERROR compilation successful
+fn main() {
 }

src/test/compile-fail/object-lifetime-default-ambiguous.rs

@@ -47,10 +47,7 @@ fn d(t: Ref2<Ref1<Test>>) {
 }
 
 fn e(t: Ref2<Ref0<Test>>) {
-    //~^ ERROR lifetime bound for this object type cannot be deduced from context
-    //
-    // In this case, Ref2 is ambiguous, and Ref0 inherits the
-    // ambiguity.
+    // In this case, Ref2 is ambiguous, but Ref0 overrides with 'static.
 }
 
 fn f(t: &Ref2<Test>) {

src/test/compile-fail/object-lifetime-default-elision.rs

@@ -34,13 +34,11 @@ fn load0<'a>(ss: &'a Box<SomeTrait>) -> Box<SomeTrait> {
     //
     // Under new rules the result is:
     //
-    // for<'a> fn(&'a Box<SomeTrait+'a>) -> Box<SomeTrait+'static>
+    // for<'a> fn(&'a Box<SomeTrait+'static>) -> Box<SomeTrait+'static>
     //
-    // Therefore, we get a type error attempting to return `deref(ss)`
-    // since `SomeTrait+'a <: SomeTrait+'static` does not hold.
+    // Therefore, no type error.
 
     deref(ss)
-        //~^ ERROR cannot infer
 }
 
 fn load1(ss: &SomeTrait) -> &SomeTrait {

src/test/compile-fail/object-lifetime-default-from-rptr-box-error.rs

@@ -0,0 +1,31 @@
+// 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 the lifetime from the enclosing `&` is "inherited"
+// through the `Box` struct.
+
+// pretty-expanded FIXME #23616
+
+#![allow(dead_code)]
+
+trait Test {
+    fn foo(&self) { }
+}
+
+struct SomeStruct<'a> {
+    t: &'a Box<Test>,
+}
+
+fn c<'a>(t: &'a Box<Test+'a>, mut ss: SomeStruct<'a>) {
+    ss.t = t; //~ ERROR mismatched types
+}
+
+fn main() {
+}

src/test/compile-fail/object-lifetime-default-from-rptr-struct-error.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.
+
+// Test that the lifetime from the enclosing `&` is "inherited"
+// through the `MyBox` struct.
+
+// pretty-expanded FIXME #23616
+
+#![allow(dead_code)]
+#![feature(rustc_error)]
+
+trait Test {
+    fn foo(&self) { }
+}
+
+struct SomeStruct<'a> {
+    t: &'a MyBox<Test>,
+    u: &'a MyBox<Test+'a>,
+}
+
+struct MyBox<T:?Sized> {
+    b: Box<T>
+}
+
+fn c<'a>(t: &'a MyBox<Test+'a>, mut ss: SomeStruct<'a>) {
+    ss.t = t; //~ ERROR mismatched types
+}
+
+fn main() {
+}

src/test/compile-fail/object-lifetime-default-mybox.rs

@@ -27,7 +27,7 @@ fn deref<T>(ss: &T) -> T {
 }
 
 fn load0(ss: &MyBox<SomeTrait>) -> MyBox<SomeTrait> {
-    deref(ss) //~ ERROR cannot infer
+    deref(ss)
 }
 
 fn load1<'a,'b>(a: &'a MyBox<SomeTrait>,
@@ -36,11 +36,10 @@ fn load1<'a,'b>(a: &'a MyBox<SomeTrait>,
 {
     a
       //~^ ERROR cannot infer
-      //~| ERROR mismatched types
 }
 
 fn load2<'a>(ss: &MyBox<SomeTrait+'a>) -> MyBox<SomeTrait+'a> {
-    load0(ss) //~ WARNING E0398
+    load0(ss) //~ ERROR mismatched types
 }
 
 fn main() {

src/test/run-pass/lang-item-public.rs

@@ -1,22 +0,0 @@
-// Copyright 2014-2015 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:lang-item-public.rs
-// ignore-android
-
-#![feature(start, no_std)]
-#![no_std]
-
-extern crate lang_item_public as lang_lib;
-
-#[start]
-fn main(_: isize, _: *const *const u8) -> isize {
-    1_isize % 1_isize
-}

src/test/run-pass/object-lifetime-default-from-rptr-box.rs

@@ -32,9 +32,7 @@ fn b<'a>(t: &'a Box<Test>, mut ss: SomeStruct<'a>) {
     ss.u = t;
 }
 
-fn c<'a>(t: &'a Box<Test+'a>, mut ss: SomeStruct<'a>) {
-    ss.t = t;
-}
+// see also compile-fail/object-lifetime-default-from-rptr-box-error.rs
 
 fn d<'a>(t: &'a Box<Test+'a>, mut ss: SomeStruct<'a>) {
     ss.u = t;

src/test/run-pass/object-lifetime-default-from-rptr-struct.rs

@@ -36,9 +36,7 @@ fn b<'a>(t: &'a MyBox<Test>, mut ss: SomeStruct<'a>) {
     ss.u = t;
 }
 
-fn c<'a>(t: &'a MyBox<Test+'a>, mut ss: SomeStruct<'a>) {
-    ss.t = t;
-}
+// see also compile-fail/object-lifetime-default-from-rptr-box-error.rs
 
 fn d<'a>(t: &'a MyBox<Test+'a>, mut ss: SomeStruct<'a>) {
     ss.u = t;