Rollup merge of #42669 - gaurikholkar:master, r=nikomatsakis

Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter

This is a fix for #42517
Note that this only handles the above case for **function declarations** and **traits**.
`impl items` and `closures` will be handled in a later PR.
Example
```
fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
    if x > y { x } else { y }
}
```
now displays the following error message. ui tests have been added for the same.
```
error[E0611]: explicit lifetime required in the type of `x`
11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
   |                     ^ consider changing the type of `x` to `&'a i32`
12 |     if x > y { x } else { y }
   |                  - lifetime `'a` required
```
#42516
r? @nikomatsakis

src/test/compile-fail/E0621-does-not-trigger-for-closures.rs

@@ -0,0 +1,28 @@
+// Copyright 2016 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 we give the generic E0495 when one of the free regions is
+// bound in a closure (rather than suggesting a change to the signature
+// of the closure, which is not specified in `foo` but rather in `invoke`).
+
+// FIXME - This might be better as a UI test, but the finer details
+// of the error seem to vary on different machines.
+fn invoke<'a, F>(x: &'a i32, f: F) -> &'a i32
+where F: FnOnce(&'a i32, &i32) -> &'a i32
+{
+    let y = 22;
+    f(x, &y)
+}
+
+fn foo<'a>(x: &'a i32) {
+    invoke(&x, |a, b| if a > b { a } else { b }); //~ ERROR E0495
+}
+
+fn main() {}

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-2.rs

@@ -0,0 +1,15 @@
+// Copyright 2016 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 foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+    if x > y { x } else { y }
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-2.stderr

@@ -0,0 +1,10 @@
+error[E0621]: explicit lifetime required in the type of `x`
+  --> $DIR/ex1-return-one-existing-name-if-else-2.rs:12:16
+   |
+11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+   |            - consider changing the type of `x` to `&'a i32`
+12 |     if x > y { x } else { y }
+   |                ^ lifetime `'a` required
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-3.rs

@@ -0,0 +1,15 @@
+// Copyright 2016 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 foo<'a>((x, y): (&'a i32, &i32)) -> &'a i32 {
+    if x > y { x } else { y }
+}
+
+fn main () { }

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-3.stderr

@@ -0,0 +1,10 @@
+error[E0621]: explicit lifetime required in parameter type
+  --> $DIR/ex1-return-one-existing-name-if-else-3.rs:12:27
+   |
+11 | fn foo<'a>((x, y): (&'a i32, &i32)) -> &'a i32 {
+   |            ------ consider changing type to `(&'a i32, &'a i32)`
+12 |     if x > y { x } else { y }
+   |                           ^ lifetime `'a` required
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl-2.rs

@@ -0,0 +1,18 @@
+// Copyright 2016 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 foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+   if x > y { x } else { y }
+   }
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl-2.stderr

@@ -0,0 +1,10 @@
+error[E0621]: explicit lifetime required in the type of `x`
+  --> $DIR/ex1-return-one-existing-name-if-else-using-impl-2.rs:14:15
+   |
+13 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+   |            - consider changing the type of `x` to `&'a i32`
+14 |    if x > y { x } else { y }
+   |               ^ lifetime `'a` required
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl-3.rs

@@ -0,0 +1,24 @@
+// Copyright 2016 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 {
+  field: i32
+}
+
+impl Foo {
+  fn foo<'a>(&'a self, x: &i32) -> &i32 {
+
+    if true { &self.field } else { x }
+
+  }
+
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl-3.stderr

@@ -0,0 +1,11 @@
+error[E0621]: explicit lifetime required in the type of `x`
+  --> $DIR/ex1-return-one-existing-name-if-else-using-impl-3.rs:18:36
+   |
+16 |   fn foo<'a>(&'a self, x: &i32) -> &i32 {
+   |                        - consider changing the type of `x` to `&'a i32`
+17 | 
+18 |     if true { &self.field } else { x }
+   |                                    ^ lifetime `'a` required
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 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 foo<'a>(x: &i32, y: &'a i32) -> &'a i32;
+
+}
+
+impl Foo for () {
+
+    fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+
+        if x > y { x } else { y }
+
+    }
+
+}
+
+fn main() {}

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl.stderr

@@ -0,0 +1,27 @@
+error[E0312]: lifetime of reference outlives lifetime of borrowed content...
+  --> $DIR/ex1-return-one-existing-name-if-else-using-impl.rs:21:20
+   |
+21 |         if x > y { x } else { y }
+   |                    ^
+   |
+note: ...the reference is valid for the lifetime 'a as defined on the method body at 19:5...
+  --> $DIR/ex1-return-one-existing-name-if-else-using-impl.rs:19:5
+   |
+19 | /     fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+20 | |
+21 | |         if x > y { x } else { y }
+22 | |
+23 | |     }
+   | |_____^
+note: ...but the borrowed content is only valid for the anonymous lifetime #1 defined on the method body at 19:5
+  --> $DIR/ex1-return-one-existing-name-if-else-using-impl.rs:19:5
+   |
+19 | /     fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
+20 | |
+21 | |         if x > y { x } else { y }
+22 | |
+23 | |     }
+   | |_____^
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else.stderr

@@ -1,23 +1,10 @@
-error[E0312]: lifetime of reference outlives lifetime of borrowed content...
+error[E0621]: explicit lifetime required in the type of `y`
   --> $DIR/ex1-return-one-existing-name-if-else.rs:12:27
    |
+11 | fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
+   |                        - consider changing the type of `y` to `&'a i32`
 12 |     if x > y { x } else { y }
-   |                           ^
-   |
-note: ...the reference is valid for the lifetime 'a as defined on the function body at 11:1...
-  --> $DIR/ex1-return-one-existing-name-if-else.rs:11:1
-   |
-11 | / fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
-12 | |     if x > y { x } else { y }
-13 | | }
-   | |_^
-note: ...but the borrowed content is only valid for the anonymous lifetime #1 defined on the function body at 11:1
-  --> $DIR/ex1-return-one-existing-name-if-else.rs:11:1
-   |
-11 | / fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
-12 | |     if x > y { x } else { y }
-13 | | }
-   | |_^
+   |                           ^ lifetime `'a` required
 
 error: aborting due to previous error(s)
 

src/test/ui/lifetime-errors/ex1-return-one-existing-name-return-type-is-anon.rs

@@ -0,0 +1,24 @@
+// Copyright 2016 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 {
+  field: i32
+}
+
+impl Foo {
+  fn foo<'a>(&self, x: &'a i32) -> &i32 {
+
+    x
+
+  }
+
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex1-return-one-existing-name-return-type-is-anon.stderr

@@ -0,0 +1,27 @@
+error[E0312]: lifetime of reference outlives lifetime of borrowed content...
+  --> $DIR/ex1-return-one-existing-name-return-type-is-anon.rs:18:5
+   |
+18 |     x
+   |     ^
+   |
+note: ...the reference is valid for the anonymous lifetime #1 defined on the method body at 16:3...
+  --> $DIR/ex1-return-one-existing-name-return-type-is-anon.rs:16:3
+   |
+16 | /   fn foo<'a>(&self, x: &'a i32) -> &i32 {
+17 | |
+18 | |     x
+19 | |
+20 | |   }
+   | |___^
+note: ...but the borrowed content is only valid for the lifetime 'a as defined on the method body at 16:3
+  --> $DIR/ex1-return-one-existing-name-return-type-is-anon.rs:16:3
+   |
+16 | /   fn foo<'a>(&self, x: &'a i32) -> &i32 {
+17 | |
+18 | |     x
+19 | |
+20 | |   }
+   | |___^
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex1-return-one-existing-name-self-is-anon.rs

@@ -0,0 +1,23 @@
+// Copyright 2016 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 {
+    field: i32,
+}
+
+impl Foo {
+    fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
+
+        if true { x } else { self }
+
+    }
+}
+
+fn main() {}

src/test/ui/lifetime-errors/ex1-return-one-existing-name-self-is-anon.stderr

@@ -0,0 +1,27 @@
+error[E0312]: lifetime of reference outlives lifetime of borrowed content...
+  --> $DIR/ex1-return-one-existing-name-self-is-anon.rs:18:30
+   |
+18 |         if true { x } else { self }
+   |                              ^^^^
+   |
+note: ...the reference is valid for the lifetime 'a as defined on the method body at 16:5...
+  --> $DIR/ex1-return-one-existing-name-self-is-anon.rs:16:5
+   |
+16 | /     fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
+17 | |
+18 | |         if true { x } else { self }
+19 | |
+20 | |     }
+   | |_____^
+note: ...but the borrowed content is only valid for the anonymous lifetime #1 defined on the method body at 16:5
+  --> $DIR/ex1-return-one-existing-name-self-is-anon.rs:16:5
+   |
+16 | /     fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
+17 | |
+18 | |         if true { x } else { self }
+19 | |
+20 | |     }
+   | |_____^
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex2a-push-one-existing-name-2.rs

@@ -0,0 +1,19 @@
+// Copyright 2016 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 Ref<'a, T: 'a> {
+    data: &'a T
+}
+
+fn foo<'a>(x: Ref<i32>, y: &mut Vec<Ref<'a, i32>>) {
+    y.push(x);
+}
+
+fn main() { }

src/test/ui/lifetime-errors/ex2a-push-one-existing-name-2.stderr

@@ -0,0 +1,10 @@
+error[E0621]: explicit lifetime required in the type of `x`
+  --> $DIR/ex2a-push-one-existing-name-2.rs:16:12
+   |
+15 | fn foo<'a>(x: Ref<i32>, y: &mut Vec<Ref<'a, i32>>) {
+   |            - consider changing the type of `x` to `Ref<'a, i32>`
+16 |     y.push(x);
+   |            ^ lifetime `'a` required
+
+error: aborting due to previous error(s)
+

src/test/ui/lifetime-errors/ex2a-push-one-existing-name.stderr

@@ -1,25 +1,10 @@
-error[E0308]: mismatched types
+error[E0621]: explicit lifetime required in the type of `y`
   --> $DIR/ex2a-push-one-existing-name.rs:16:12
    |
+15 | fn foo<'a>(x: &mut Vec<Ref<'a, i32>>, y: Ref<i32>) {
+   |                                       - consider changing the type of `y` to `Ref<'a, i32>`
 16 |     x.push(y);
-   |            ^ lifetime mismatch
-   |
-   = note: expected type `Ref<'a, _>`
-              found type `Ref<'_, _>`
-note: the anonymous lifetime #2 defined on the function body at 15:1...
-  --> $DIR/ex2a-push-one-existing-name.rs:15:1
-   |
-15 | / fn foo<'a>(x: &mut Vec<Ref<'a, i32>>, y: Ref<i32>) {
-16 | |     x.push(y);
-17 | | }
-   | |_^
-note: ...does not necessarily outlive the lifetime 'a as defined on the function body at 15:1
-  --> $DIR/ex2a-push-one-existing-name.rs:15:1
-   |
-15 | / fn foo<'a>(x: &mut Vec<Ref<'a, i32>>, y: Ref<i32>) {
-16 | |     x.push(y);
-17 | | }
-   | |_^
+   |            ^ lifetime `'a` required
 
 error: aborting due to previous error(s)