review updates to E0311 description

diff --git a/compiler/rustc_error_codes/src/error_codes/E0311.md b/compiler/rustc_error_codes/src/error_codes/E0311.md
index bc75a1f7f5e6a415da0f83e5463e4d6068201258..638c3e0a4373f62c778d18a218bfb7dd336b05da 100644 (file)
--- a/compiler/rustc_error_codes/src/error_codes/E0311.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0311.md
@@ -14,33 +14,25 @@ fn with_restriction<'a, T: 'a>(x: &'a ()) -> &'a () {
 ```
 
 Why doesn't this code compile? It helps to look at the lifetime bounds that are
-automatically adding by the compiler. For more details see the Rust
-Documentation for Lifetime Elision:
-https://doc.rust-lang.org/reference/lifetime-elision.html.
+automatically added by the compiler. For more details see the documentation for
+[lifetime elision]( https://doc.rust-lang.org/reference/lifetime-elision.html).
 
-There are two lifetimes being passed into the `no_restriction()` function: one
-associated with the generic type `T` parameter and the other with the input
-argument `x`. The compiler does not know which of these lifetimes can be
-assigned to the output reference, so we get an error.
+The compiler elides the lifetime of `x` and the return type to some arbitrary
+lifetime `'anon` in `no_restriction()`. The only information available to the
+compiler is that `'anon` is valid for the duration of the function. When
+calling `with_restriction()`, the compiler requires the completely unrelated
+type parameter `T` to outlive `'anon` because of the `T: 'a bound` in
+`with_restriction()`. This causes an error because `T` is not required to
+outlive `'anon` in `no_restriction()`.
 
-One way to "fix" this code would be to remove the generic type argument `T`.
-In this case, the lifetime elision works because there is a single input
-lifetime, which is associated with `x`.
+If `no_restriction()` were to use `&T` instead of `&()` as an argument, the
+compiler would have added an implied bound [implied
+bound](https://rust-lang.github.io/rfcs/2089-implied-bounds.html), causing this
+to compile.
 
-```
-fn no_restriction(x: &()) -> &() {
-    with_restriction(x)
-}
-
-fn with_restriction<'a>(x: &'a ()) -> &'a () {
-    x
-}
-```
+This error can be resolved by explicitly naming the elided lifetime for `x` and
+then explicily requiring that the generic parameter `T` outlives that lifetime:
 
-The "correct" way to resolve this error is to explicitly tell the compiler
-which input lifetime should be assigned to the output. In this case we give
-both the generic type `T` parameter and the argument `x` the same lifetime
-requirement as the output reference, producing a working version of the code:
 ```
 fn no_restriction<'a, T: 'a>(x: &'a ()) -> &'a () {
     with_restriction::<T>(x)