Rollup merge of rust-lang#104266 - compiler-errors:issue-102430, r=Mark-Simulacrum

Regression test for coercion of mut-ref to dyn-star

Closes rust-lang#102430

Author: Manishearth

src/test/ui/dyn-star/issue-102430.rs

@@ -0,0 +1,32 @@
+// check-pass
+
+#![feature(dyn_star)]
+#![allow(incomplete_features)]
+
+trait AddOne {
+    fn add1(&mut self) -> usize;
+}
+
+impl AddOne for usize {
+    fn add1(&mut self) -> usize {
+        *self += 1;
+        *self
+    }
+}
+
+impl AddOne for &mut usize {
+    fn add1(&mut self) -> usize {
+        (*self).add1()
+    }
+}
+
+fn add_one(mut i: dyn* AddOne + '_) -> usize {
+    i.add1()
+}
+
+fn main() {
+    let mut x = 42usize;
+    let y = &mut x as (dyn* AddOne + '_);
+
+    println!("{}", add_one(y));
+}