Rust error E0457: #### Note: this error code is no longer emitted by the compiler

The compiler team's explanation

Note: this error code is no longer emitted by the compiler

Plugin .. only found in rlib format, but must be available in dylib format.

Erroneous code example:

rlib-plugin.rs

#![crate_type = "rlib"]
#![feature(rustc_private)]

extern crate rustc_middle;
extern crate rustc_driver;

use rustc_driver::plugin::Registry;

#[no_mangle]
fn __rustc_plugin_registrar(_: &mut Registry) {}

main.rs

#![feature(plugin)]
#![plugin(rlib_plugin)] // error: plugin `rlib_plugin` only found in rlib
                        //        format, but must be available in dylib

fn main() {}

The compiler exposes a plugin interface to allow altering the compile process (adding lints, etc). Plugins must be defined in their own crates (similar to proc-macro isolation) and then compiled and linked to another crate. Plugin crates *must* be compiled to the dynamically-linked dylib format, and not the statically-linked rlib format. Learn more about different output types in this section of the Rust reference.

This error is easily fixed by recompiling the plugin crate in the dylib format.

From rustc --explain E0457 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.