error: calling `.extend(_.chars())`
  --> $DIR/string_extend.rs:16:5
   |
16 |     s.extend(abc.chars());
   |     ^^^^^^^^^^^^^^^^^^^^^ help: try this: `s.push_str(abc)`
   |
   = note: `-D string-extend-chars` implied by `-D warnings`

error: calling `.extend(_.chars())`
  --> $DIR/string_extend.rs:19:5
   |
19 |     s.extend("abc".chars());
   |     ^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `s.push_str("abc")`

error: calling `.extend(_.chars())`
  --> $DIR/string_extend.rs:22:5
   |
22 |     s.extend(def.chars());
   |     ^^^^^^^^^^^^^^^^^^^^^ help: try this: `s.push_str(&def)`

error: aborting due to 3 previous errors