Understanding Rust Error E0457
Rust Error E0457: Plugin only found in rlib format, but must be available in dylib format
When working with Rust plugins, you may encounter the error E0457, which indicates that a plugin was found in rlib format instead of the required dylib format. Plugins are essentially custom compiler extensions that allow you to modify the compilation process, such as adding lints or custom syntax. To use a plugin, your program must meet certain criteria:
1. Plugins must be defined in their own crates (similar to proc-macro isolation).
2. Plugin crates must be compiled to the dynamically-linked dylib format, not the statically-linked rlib format.
Understanding the error
The error occurs when you attempt to use a plugin that has been compiled in the wrong format, specifically the rlib format. To fix the error, you need to recompile the plugin crate in the dylib format.
Examining the error 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 given code above demonstrates the error, where 'rlib-plugin.rs' is compiled with the crate_type attribute set to rlib. When attempting to use the plugin in 'main.rs', the compiler throws Error E0457.
Fixing the error
To fix the error, change the crate_type attribute to dylib in the plugin crate, recompile, and update any relevant build scripts. Here's the corrected code for 'rlib-plugin.rs':
rlib-plugin.rs#![crate_type = "dylib"]
#![feature(rustc_private)]
extern crate rustc_middle;
extern crate rustc_driver;
use rustc_driver::plugin::Registry;
#[no_mangle]
fn __rustc_plugin_registrar(_: &mut Registry) {}
Now, when you compile with the corrected plugin crate, Error E0457 should not occur.