easy-plugin 0.11.1

A compiler plugin that makes it easier to write compiler plugins.
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A compiler plugin that makes it easier to write compiler plugins.

Released under the Apache License 2.0.

Supported Configurations

By default, easy-plugin expects to be compiled by a nightly Rust compiler. easy-plugin is also supported on the stable and beta channels of Rust with syntex. To enable this support, enable the stable Cargo feature.


The following usage of easy_plugin! defines a plugin which accepts key-value pairs.

easy_plugin! {
    // A key can either be an identifier or a string literal.
    enum Key {
        Ident { $key:ident },
        Lit { $key:lit_str },

    // A key-value pair is a key followed by `=>` and any expression.
    struct KeyValuePair {
        $key:$Key => $value:expr

    // This plugin accepts one or more comma-separated key-value pairs.
    struct Arguments {
        $($kvp:$KeyValuePair), + $(,)?

    pub fn expand_kvp(
        _: &mut ExtCtxt, span: Span, arguments: Arguments
    ) -> PluginResult<Box<MacResult>> {
        for KeyValuePair { key, value } in arguments.kvp {
            match key {
                Key::Ident { key } => println!("Key:   {}", key.node),
                Key::Lit { key } => println!("Key:   {:?}", key.0),
            println!("Value: {}", pprust::expr_to_string(&value));

pub fn plugin_registrar(registry: &mut Registry) {
    registry.register_macro("kvp", expand_kvp);