add comment dyn-iterator-deref-in-for-loop.rs

Author: reddevilmidzy

tests/ui/traits/dyn-iterator-deref-in-for-loop.current.stderr

@@ -1,14 +1,14 @@
 error[E0277]: `dyn Iterator<Item = &'a mut u8>` is not an iterator
-  --> $DIR/issue-20605.rs:6:17
+  --> $DIR/dyn-iterator-deref-in-for-loop.rs:9:17
    |
-LL |     for item in *things { *item = 0 }
+LL |     for item in *things {
    |                 ^^^^^^^ the trait `IntoIterator` is not implemented for `dyn Iterator<Item = &'a mut u8>`
    |
    = note: the trait bound `dyn Iterator<Item = &'a mut u8>: IntoIterator` is not satisfied
    = note: required for `dyn Iterator<Item = &'a mut u8>` to implement `IntoIterator`
 help: consider mutably borrowing here
    |
-LL |     for item in &mut *things { *item = 0 }
+LL |     for item in &mut *things {
    |                 ++++
 
 error: aborting due to 1 previous error

tests/ui/traits/dyn-iterator-deref-in-for-loop.next.stderr

@@ -1,14 +1,14 @@
 error[E0277]: `dyn Iterator<Item = &'a mut u8>` is not an iterator
-  --> $DIR/issue-20605.rs:6:17
+  --> $DIR/dyn-iterator-deref-in-for-loop.rs:9:17
    |
-LL |     for item in *things { *item = 0 }
+LL |     for item in *things {
    |                 ^^^^^^^ the trait `IntoIterator` is not implemented for `dyn Iterator<Item = &'a mut u8>`
    |
    = note: the trait bound `dyn Iterator<Item = &'a mut u8>: IntoIterator` is not satisfied
    = note: required for `dyn Iterator<Item = &'a mut u8>` to implement `IntoIterator`
 help: consider mutably borrowing here
    |
-LL |     for item in &mut *things { *item = 0 }
+LL |     for item in &mut *things {
    |                 ++++
 
 error: aborting due to 1 previous error

tests/ui/traits/dyn-iterator-deref-in-for-loop.rs

@@ -1,10 +1,15 @@
+//! Tests that dereferencing a Box<dyn Iterator> in a for loop correctly yields an error,
+//! as the unsized trait object does not implement IntoIterator.
+//! regression test for <https://github.com/rust-lang/rust/issues/20605>
 //@ revisions: current next
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-fn changer<'a>(mut things: Box<dyn Iterator<Item=&'a mut u8>>) {
-    for item in *things { *item = 0 }
-    //~^ ERROR `dyn Iterator<Item = &'a mut u8>` is not an iterator
+fn changer<'a>(mut things: Box<dyn Iterator<Item = &'a mut u8>>) {
+    for item in *things {
+        //~^ ERROR `dyn Iterator<Item = &'a mut u8>` is not an iterator
+        *item = 0
+    }
 }
 
 fn main() {}