error[E0384]: cannot assign twice to immutable variable `x`
  --> $DIR/command-line-diagnostics.rs:6:5
   |
LL |     let x = 42;
   |         - first assignment to `x`
LL |     x = 43;
   |     ^^^^^^ cannot assign twice to immutable variable
   |
help: consider making this binding mutable
   |
LL |     let mut x = 42;
   |         +++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0384`.