Handle anon lifetime arg being returned with named lifetime return type

When there's a lifetime mismatch between an argument with an anonymous
lifetime being returned in a method with a return type that has a named
lifetime, show specialized lifetime error pointing at argument with a
hint to give it an explicit lifetime matching the return type.

```
error[E0621]: explicit lifetime required in the type of `other`
  --> file2.rs:21:21
   |
17 |     fn bar(&self, other: Foo) -> Foo<'a> {
   |                   ----- consider changing the type of `other` to `Foo<'a>`
...
21 |                     other
   |                     ^^^^^ lifetime `'a` required
```

Follow up to #44124 and #42669.

3 files changed, 44 insertions, 3 deletions

diff --git a/src/test/ui/lifetime-errors/ex3-both-anon-regions-earlybound-regions.stderr b/src/test/ui/lifetime-errors/ex3-both-anon-regions-earlybound-regions.stderr
index 58f2cb94cec..6c5ed672604 100644
--- a/src/test/ui/lifetime-errors/ex3-both-anon-regions-earlybound-regions.stderr
+++ b/src/test/ui/lifetime-errors/ex3-both-anon-regions-earlybound-regions.stderr
@@ -1,11 +1,11 @@
-error[E0623]: lifetime mismatch
+error[E0621]: explicit lifetime required in the type of `y`
   --> $DIR/ex3-both-anon-regions-earlybound-regions.rs:17:12
    |
 13 | fn baz<'a, 'b, T>(x: &mut Vec<&'a T>, y: &T)
-   |                               -----      -- these two types are declared with different lifetimes...
+   |                                       - consider changing the type of `y` to `&'a T`
 ...
 17 |     x.push(y);
-   |            ^ ...but data from `y` flows into `x` here
+   |            ^ lifetime `'a` required
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/lifetime-errors/ex4-anon-named-regions.rs b/src/test/ui/lifetime-errors/ex4-anon-named-regions.rs
new file mode 100644
index 00000000000..55752f753ef
--- /dev/null
+++ b/src/test/ui/lifetime-errors/ex4-anon-named-regions.rs
@@ -0,0 +1,30 @@
+// 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.
+
+#[derive(Clone)]
+enum Foo<'a> {
+    Bar(&'a str),
+}
+
+impl<'a> Foo<'a> {
+    fn bar(&self, other: Foo) -> Foo<'a> {
+        match *self {
+            Foo::Bar(s) => {
+                if s == "test" {
+                    other
+                } else {
+                    self.clone()
+                }
+            }
+        }
+    }
+}
+
+fn main() { }
diff --git a/src/test/ui/lifetime-errors/ex4-anon-named-regions.stderr b/src/test/ui/lifetime-errors/ex4-anon-named-regions.stderr
new file mode 100644
index 00000000000..4a127bbc551
--- /dev/null
+++ b/src/test/ui/lifetime-errors/ex4-anon-named-regions.stderr
@@ -0,0 +1,11 @@
+error[E0621]: explicit lifetime required in the type of `other`
+  --> $DIR/ex4-anon-named-regions.rs:21:21
+   |
+17 |     fn bar(&self, other: Foo) -> Foo<'a> {
+   |                   ----- consider changing the type of `other` to `Foo<'a>`
+...
+21 |                     other
+   |                     ^^^^^ lifetime `'a` required
+
+error: aborting due to previous error
+