add comment in iter-from-mac-call.rs

Author: reddevilmidzy

tests/ui/for-loop-while/iter-from-mac-call.rs

@@ -1,10 +1,17 @@
+//! Tests that trait resolution errors (like non-iterator dereference) are correctly reported
+//! when the dereference operation is encapsulated within a macro.
+
 macro_rules! deref {
-    ($e:expr) => { *$e };
+    ($e:expr) => {
+        *$e
+    };
 }
 
-fn f1<'a>(mut iter: Box<dyn Iterator<Item=&'a mut u8>>) {
-    for item in deref!(iter) { *item = 0 }
-    //~^ ERROR `dyn Iterator<Item = &'a mut u8>` is not an iterator
+fn f1<'a>(mut iter: Box<dyn Iterator<Item = &'a mut u8>>) {
+    for item in deref!(iter) {
+        //~^ ERROR `dyn Iterator<Item = &'a mut u8>` is not an iterator
+        *item = 0
+    }
 }
 
 fn f2(x: &mut i32) {
@@ -15,12 +22,16 @@ fn f2(x: &mut i32) {
 struct Wrapped(i32);
 
 macro_rules! borrow_deref {
-    ($e:expr) => { &mut *$e };
+    ($e:expr) => {
+        &mut *$e
+    };
 }
 
-fn f3<'a>(mut iter: Box<dyn Iterator<Item=&'a mut i32>>) {
-    for Wrapped(item) in borrow_deref!(iter) { *item = 0 }
-    //~^ ERROR mismatched types
+fn f3<'a>(mut iter: Box<dyn Iterator<Item = &'a mut i32>>) {
+    for Wrapped(item) in borrow_deref!(iter) {
+        //~^ ERROR mismatched types
+        *item = 0
+    }
 }
 
 fn main() {}

tests/ui/for-loop-while/iter-from-mac-call.stderr

@@ -1,18 +1,18 @@
 error[E0277]: `dyn Iterator<Item = &'a mut u8>` is not an iterator
-  --> $DIR/iter_from_mac_call.rs:6:17
+  --> $DIR/iter-from-mac-call.rs:11:17
    |
-LL |     for item in deref!(iter) { *item = 0 }
+LL |     for item in deref!(iter) {
    |                 ^^^^^^^^^^^^ 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 deref!(iter) { *item = 0 }
+LL |     for item in &mut deref!(iter) {
    |                 ++++
 
 error[E0277]: `i32` is not an iterator
-  --> $DIR/iter_from_mac_call.rs:11:18
+  --> $DIR/iter-from-mac-call.rs:18:18
    |
 LL |     for _item in deref!(x) {}
    |                  ^^^^^^^^^ `i32` is not an iterator
@@ -22,9 +22,9 @@ LL |     for _item in deref!(x) {}
    = note: required for `i32` to implement `IntoIterator`
 
 error[E0308]: mismatched types
-  --> $DIR/iter_from_mac_call.rs:22:9
+  --> $DIR/iter-from-mac-call.rs:31:9
    |
-LL |     for Wrapped(item) in borrow_deref!(iter) { *item = 0 }
+LL |     for Wrapped(item) in borrow_deref!(iter) {
    |         ^^^^^^^^^^^^^    ------------------- this is an iterator with items of type `&mut i32`
    |         |
    |         expected `i32`, found `Wrapped`