don't refer to async as 'generators'

and give return of async fn a better span

src/test/ui/async-await/issue-74072-lifetime-name-annotations.rs

@@ -0,0 +1,29 @@
+// edition:2018
+#![feature(async_closure)]
+use std::future::Future;
+
+// test the quality of annotations giving lifetimes names (`'1`) when async constructs are involved
+
+pub async fn async_fn(x: &mut i32) -> &i32 {
+    let y = &*x;
+    *x += 1; //~ ERROR cannot assign to `*x` because it is borrowed
+    y
+}
+
+pub fn async_closure(x: &mut i32) -> impl Future<Output=&i32> {
+    (async move || {
+        let y = &*x;
+        *x += 1; //~ ERROR cannot assign to `*x` because it is borrowed
+        y
+    })()
+}
+
+pub fn async_block(x: &mut i32) -> impl Future<Output=&i32> {
+    async move {
+        let y = &*x;
+        *x += 1; //~ ERROR cannot assign to `*x` because it is borrowed
+        y
+    }
+}
+
+fn main() {}

src/test/ui/async-await/issue-74072-lifetime-name-annotations.stderr

@@ -0,0 +1,39 @@
+error[E0506]: cannot assign to `*x` because it is borrowed
+  --> $DIR/issue-74072-lifetime-name-annotations.rs:9:5
+   |
+LL | pub async fn async_fn(x: &mut i32) -> &i32 {
+   |                                       ---- return type of async function is &'1 i32
+LL |     let y = &*x;
+   |             --- borrow of `*x` occurs here
+LL |     *x += 1;
+   |     ^^^^^^^ assignment to borrowed `*x` occurs here
+LL |     y
+   |     - returning this value requires that `*x` is borrowed for `'1`
+
+error[E0506]: cannot assign to `*x` because it is borrowed
+  --> $DIR/issue-74072-lifetime-name-annotations.rs:16:9
+   |
+LL |         let y = &*x;
+   |                 --- borrow of `*x` occurs here
+LL |         *x += 1;
+   |         ^^^^^^^ assignment to borrowed `*x` occurs here
+LL |         y
+   |         - returning this value requires that `*x` is borrowed for `'1`
+LL |     })()
+   |     - return type of async closure is &'1 i32
+
+error[E0506]: cannot assign to `*x` because it is borrowed
+  --> $DIR/issue-74072-lifetime-name-annotations.rs:24:9
+   |
+LL |         let y = &*x;
+   |                 --- borrow of `*x` occurs here
+LL |         *x += 1;
+   |         ^^^^^^^ assignment to borrowed `*x` occurs here
+LL |         y
+   |         - returning this value requires that `*x` is borrowed for `'1`
+LL |     }
+   |     - return type of async block is &'1 i32
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0506`.