Add regression ui test for #139839

Author: GuillaumeGomez

tests/ui/async-gen-move-suggestion.fixed

@@ -0,0 +1,24 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/139839>.
+// It ensures that the "add `move` keyword" suggestion is valid.
+
+//@ run-rustfix
+//@ edition:2024
+
+#![feature(coroutines)]
+#![feature(gen_blocks)]
+#![feature(async_iterator)]
+
+use std::async_iter::AsyncIterator;
+
+#[allow(dead_code)]
+fn moved() -> impl AsyncIterator<Item = u32> {
+    let mut x = "foo".to_string();
+
+    async gen move { //~ ERROR
+        x.clear();
+        for x in 3..6 { yield x }
+    }
+}
+
+fn main() {
+}

tests/ui/async-gen-move-suggestion.rs

@@ -0,0 +1,24 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/139839>.
+// It ensures that the "add `move` keyword" suggestion is valid.
+
+//@ run-rustfix
+//@ edition:2024
+
+#![feature(coroutines)]
+#![feature(gen_blocks)]
+#![feature(async_iterator)]
+
+use std::async_iter::AsyncIterator;
+
+#[allow(dead_code)]
+fn moved() -> impl AsyncIterator<Item = u32> {
+    let mut x = "foo".to_string();
+
+    async gen { //~ ERROR
+        x.clear();
+        for x in 3..6 { yield x }
+    }
+}
+
+fn main() {
+}

tests/ui/async-gen-move-suggestion.stderr

@@ -0,0 +1,24 @@
+error[E0373]: async gen block may outlive the current function, but it borrows `x`, which is owned by the current function
+  --> $DIR/async-gen-move-suggestion.rs:17:5
+   |
+LL |     async gen {
+   |     ^^^^^^^^^ may outlive borrowed value `x`
+LL |         x.clear();
+   |         - `x` is borrowed here
+   |
+note: async gen block is returned here
+  --> $DIR/async-gen-move-suggestion.rs:17:5
+   |
+LL | /     async gen {
+LL | |         x.clear();
+LL | |         for x in 3..6 { yield x }
+LL | |     }
+   | |_____^
+help: to force the async gen block to take ownership of `x` (and any other referenced variables), use the `move` keyword
+   |
+LL |     async gen move {
+   |               ++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0373`.