error[E0368]: binary assignment operation `+=` cannot be applied to type `&str`
  --> $DIR/issue-10401.rs:3:5
   |
LL |     a += { "b" };
   |     -^^^^^^^^^^^
   |     |
   |     cannot use `+=` on type `&str`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0368`.