add test

src/test/ui/borrowck/issue-82032.rs

@@ -0,0 +1,16 @@
+use std::{fs, io::*};
+use std::collections::HashMap;
+
+type Handle = BufWriter<fs::File>;
+struct Thing(HashMap<String, Handle>);
+
+impl Thing {
+    pub fn die_horribly(&mut self) {
+        for v in self.0.values() {
+            v.flush();
+              //~^ ERROR cannot borrow
+        }
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-82032.stderr

@@ -0,0 +1,14 @@
+error[E0596]: cannot borrow `*v` as mutable, as it is behind a `&` reference
+  --> $DIR/issue-82032.rs:10:13
+   |
+LL |         for v in self.0.values() {
+   |                  ---------------
+   |                  |      |
+   |                  |      help: use mutable method: `values_mut()`
+   |                  this iterator yields `&` references
+LL |             v.flush();
+   |             ^ `v` is a `&` reference, so the data it refers to cannot be borrowed as mutable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.