error[E0505]: cannot move out of `a` because it is borrowed
  --> $DIR/borrow-for-loop-head.rs:4:18
   |
LL |     let a = vec![1, 2, 3];
   |         - binding `a` declared here
LL |     for i in &a {
   |              -- borrow of `a` occurs here
LL |         for j in a {
   |                  ^ move out of `a` occurs here
   |
help: consider cloning the value if the performance cost is acceptable
   |
LL |     for i in &a.clone() {
   |                ++++++++

error[E0382]: use of moved value: `a`
  --> $DIR/borrow-for-loop-head.rs:4:18
   |
LL |     let a = vec![1, 2, 3];
   |         - move occurs because `a` has type `Vec<i32>`, which does not implement the `Copy` trait
LL |     for i in &a {
   |     ----------- inside of this loop
LL |         for j in a {
   |                  ^ `a` moved due to this implicit call to `.into_iter()`, in previous iteration of loop
   |
note: `into_iter` takes ownership of the receiver `self`, which moves `a`
  --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
help: consider iterating over a slice of the `Vec<i32>`'s content to avoid moving into the `for` loop
   |
LL |         for j in &a {
   |                  +

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0382, E0505.
For more information about an error, try `rustc --explain E0382`.