Rollup merge of #68908 - jwhite927:E0637, r=Dylan-DPC

Add long error code explanation message for E0637

Reference issue [#61137](https://github.com/rust-lang/rust/issues/61137)
To incorporate a long error description for E0637, I have made the necessary modification to error_codes.rs and added error_codes/E0637.md, and blessed the relevant .stderror files. ~~, however when I build rustc stage 1, I am unable to make `$ rustc --explain E0637` work even though rustc appears to be able to call up the long error explanations for other errors. I wanted to guarantee this would work before moving on the blessing the various ui tests that have been affected. @GuillaumeGomez Do you know the most likely reason(s) why this would be the case?~~
Update: `$ rustc --explain E0637` works now.

src/librustc_error_codes/error_codes.rs

@@ -353,6 +353,7 @@ E0631: include_str!("./error_codes/E0631.md"),
 E0633: include_str!("./error_codes/E0633.md"),
 E0635: include_str!("./error_codes/E0635.md"),
 E0636: include_str!("./error_codes/E0636.md"),
+E0637: include_str!("./error_codes/E0637.md"),
 E0638: include_str!("./error_codes/E0638.md"),
 E0639: include_str!("./error_codes/E0639.md"),
 E0641: include_str!("./error_codes/E0641.md"),
@@ -584,7 +585,6 @@ E0746: include_str!("./error_codes/E0746.md"),
     E0632, // cannot provide explicit generic arguments when `impl Trait` is
            // used in argument position
     E0634, // type has conflicting packed representaton hints
-    E0637, // "'_" is not a valid lifetime bound
     E0640, // infer outlives requirements
 //  E0645, // trait aliases not finished
     E0657, // `impl Trait` can only capture lifetimes bound at the fn level

src/librustc_error_codes/error_codes/E0637.md

@@ -0,0 +1,32 @@
+An underscore `_` character has been used as the identifier for a lifetime.
+
+Erroneous example:
+```compile_fail,E0106,E0637
+fn longest<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
+         //^^ `'_` is a reserved lifetime name
+    if str1.len() > str2.len() {
+        str1
+    } else {
+        str2
+    }
+}
+```
+`'_`, cannot be used as a lifetime identifier because it is a reserved for the
+anonymous lifetime. To fix this, use a lowercase letter such as 'a, or a series
+of lowercase letters such as `'foo`.  For more information, see [the
+book][bk-no].  For more information on using the anonymous lifetime in rust
+nightly, see [the nightly book][bk-al].
+
+Corrected example:
+```
+fn longest<'a>(str1: &'a str, str2: &'a str) -> &'a str {
+    if str1.len() > str2.len() {
+        str1
+    } else {
+        str2
+    }
+}
+```
+
+[bk-no]: https://doc.rust-lang.org/book/appendix-02-operators.html#non-operator-symbols
+[bk-al]: https://doc.rust-lang.org/nightly/edition-guide/rust-2018/ownership-and-lifetimes/the-anonymous-lifetime.html

src/test/ui/const-generics/const-param-elided-lifetime.stderr

@@ -38,3 +38,4 @@ LL | #![feature(const_generics)]
 
 error: aborting due to 5 previous errors
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/error-codes/E0637.stderr

@@ -18,3 +18,4 @@ LL | impl<'a: '_> Bar<'a> {
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/generics/issue-65285-incorrect-explicit-lifetime-name-needed.stderr

@@ -18,4 +18,5 @@ LL | fn bar<'b, L: X<&'b Nested<i32>>>(){}
 
 error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0106`.
+Some errors have detailed explanations: E0106, E0637.
+For more information about an error, try `rustc --explain E0106`.

src/test/ui/underscore-lifetime/in-binder.stderr

@@ -36,3 +36,4 @@ LL | fn foo<'_>() {
 
 error: aborting due to 6 previous errors
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/underscore-lifetime-binders.stderr

@@ -38,4 +38,5 @@ LL | fn foo2<'a>(_: &'a u8, y: &'a u8) -> &'a u8 { y }
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0106`.
+Some errors have detailed explanations: E0106, E0637.
+For more information about an error, try `rustc --explain E0106`.

src/test/ui/underscore-lifetime/underscore-outlives-bounds.stderr

@@ -6,3 +6,4 @@ LL | impl<'b: '_> Foo<'b> for i32 {}
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-inherent-impl-ampersand.rust2015.stderr

@@ -6,3 +6,4 @@ LL |     T: WithType<&u32>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-inherent-impl-ampersand.rust2018.stderr

@@ -6,3 +6,4 @@ LL |     T: WithType<&u32>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-inherent-impl-underscore.rust2015.stderr

@@ -6,3 +6,4 @@ LL |     T: WithRegion<'_>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-inherent-impl-underscore.rust2018.stderr

@@ -6,3 +6,4 @@ LL |     T: WithRegion<'_>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-trait-impl-region.rust2015.stderr

@@ -6,3 +6,4 @@ LL |     T: WithType<&u32>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-trait-impl-region.rust2018.stderr

@@ -6,3 +6,4 @@ LL |     T: WithType<&u32>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-trait-impl-underscore.rust2015.stderr

@@ -6,3 +6,4 @@ LL |     T: WithRegion<'_>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clause-trait-impl-underscore.rust2018.stderr

@@ -6,3 +6,4 @@ LL |     T: WithRegion<'_>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/underscore-lifetime/where-clauses.stderr

@@ -12,3 +12,4 @@ LL | impl<T: '_> Foo<'static> for Vec<T> {}
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0637`.