error: using `to_string` in `fmt::Display` implementation might lead to infinite recursion
  --> $DIR/to_string_in_display.rs:25:25
   |
LL |         write!(f, "{}", self.to_string())
   |                         ^^^^^^^^^^^^^^^^
   |
   = note: `-D clippy::to-string-in-display` implied by `-D warnings`

error: unnecessary use of `to_string`
  --> $DIR/to_string_in_display.rs:55:50
   |
LL |             Self::E(string) => write!(f, "E {}", string.to_string()),
   |                                                  ^^^^^^^^^^^^^^^^^^
   |
   = note: `-D clippy::unnecessary-to-owned` implied by `-D warnings`
   = note: this error originates in the macro `$crate::format_args` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 2 previous errors