Rollup merge of #89922 - JohnTitor:update-e0637, r=jackh726

Update E0637 description to mention `&` w/o an explicit lifetime name

Deal with https://github.com/rust-lang/rust/issues/89824#issuecomment-941598647. Another solution would be splitting the error code into two as (I think) it's a bit unclear to users why they have the same error code.

2 files changed, 32 insertions, 17 deletions

diff --git a/src/test/ui/error-codes/E0637.rs b/src/test/ui/error-codes/E0637.rs
index b4888d4af6a..382ce3ed01f 100644
--- a/src/test/ui/error-codes/E0637.rs
+++ b/src/test/ui/error-codes/E0637.rs
@@ -1,9 +1,17 @@
-struct Foo<'a: '_>(&'a u8); //~ ERROR cannot be used here
-fn foo<'a: '_>(_: &'a u8) {} //~ ERROR cannot be used here
+fn underscore_lifetime<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
+    //~^ ERROR: `'_` cannot be used here [E0637]
+    //~| ERROR: missing lifetime specifier
+    if str1.len() > str2.len() {
+        str1
+    } else {
+        str2
+    }
+}
 
-struct Bar<'a>(&'a u8);
-impl<'a: '_> Bar<'a> { //~ ERROR cannot be used here
-  fn bar() {}
+fn and_without_explicit_lifetime<T>()
+where
+    T: Into<&u32>, //~ ERROR: `&` without an explicit lifetime name cannot be used here [E0637]
+{
 }
 
 fn main() {}
diff --git a/src/test/ui/error-codes/E0637.stderr b/src/test/ui/error-codes/E0637.stderr
index d19ebfd15a5..87aaba65a73 100644
--- a/src/test/ui/error-codes/E0637.stderr
+++ b/src/test/ui/error-codes/E0637.stderr
@@ -1,21 +1,28 @@
 error[E0637]: `'_` cannot be used here
-  --> $DIR/E0637.rs:1:16
+  --> $DIR/E0637.rs:1:24
    |
-LL | struct Foo<'a: '_>(&'a u8);
-   |                ^^ `'_` is a reserved lifetime name
+LL | fn underscore_lifetime<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
+   |                        ^^ `'_` is a reserved lifetime name
 
-error[E0637]: `'_` cannot be used here
-  --> $DIR/E0637.rs:2:12
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/E0637.rs:13:13
    |
-LL | fn foo<'a: '_>(_: &'a u8) {}
-   |            ^^ `'_` is a reserved lifetime name
+LL |     T: Into<&u32>,
+   |             ^ explicit lifetime name needed here
 
-error[E0637]: `'_` cannot be used here
-  --> $DIR/E0637.rs:5:10
+error[E0106]: missing lifetime specifier
+  --> $DIR/E0637.rs:1:62
+   |
+LL | fn underscore_lifetime<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
+   |                                  -------        -------      ^^ expected named lifetime parameter
+   |
+   = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `str1` or `str2`
+help: consider introducing a named lifetime parameter
    |
-LL | impl<'a: '_> Bar<'a> {
-   |          ^^ `'_` is a reserved lifetime name
+LL | fn underscore_lifetime<'a, '_>(str1: &'a str, str2: &'a str) -> &'a str {
+   |                        +++            ~~             ~~          ~~
 
 error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0637`.
+Some errors have detailed explanations: E0106, E0637.
+For more information about an error, try `rustc --explain E0106`.