Dele e0231

compiler/rustc_error_codes/src/error_codes/E0231.md

@@ -1,24 +1 @@
-The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
-message for when a particular trait isn't implemented on a type placed in a
-position that needs that trait. For example, when the following code is
-compiled:
-
-```compile_fail,E0231
-#![feature(rustc_attrs)]
-#![allow(internal_features)]
-
-#[rustc_on_unimplemented = "error on `{Self}` with params `<{A},{}>`"] // error!
-trait BadAnnotation<A> {}
-```
-
-there will be an error about `bool` not implementing `Index<u8>`, followed by a
-note saying "the type `bool` cannot be indexed by `u8`".
-
-As you can see, you can specify type parameters in curly braces for
-instantiation with the actual types (using the regular format string syntax) in
-a given situation. Furthermore, `{Self}` will be instantiated to the type (in
-this case, `bool`) that we tried to use.
-
-This error appears when the curly braces do not contain an identifier. Please
-add one of the same name as a type parameter. If you intended to use literal
-braces, use `{{` and `}}` to escape them.
+#### Note: this error code is no longer emitted by the compiler