warning: variable `x` is assigned to, but never used
 --> examples_tests/rustc_basic/aux_derive.rs:7:9
  |
7 |     let x = Foo;
  |         ^
  |
  = note: consider using `_x` instead
  = note: `#[warn(unused_variables)]` on by default

warning: value assigned to `x` is never read
 --> examples_tests/rustc_basic/aux_derive.rs:8:5
  |
8 |     x = Foo;
  |     ^
  |
  = help: maybe it is overwritten before being read?
  = note: `#[warn(unused_assignments)]` on by default

error[E0384]: cannot assign twice to immutable variable `x`
 --> examples_tests/rustc_basic/aux_derive.rs:8:5
  |
7 |     let x = Foo;
  |         - first assignment to `x`
8 |     x = Foo;
  |     ^^^^^^^ cannot assign twice to immutable variable
  |
help: consider making this binding mutable
  |
7 |     let mut x = Foo;
  |         +++

error: aborting due to 1 previous error; 2 warnings emitted

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