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//! ## Defining procedural macros
//!
//! Two crates are required to define a macro.
//!
//! ### The declaration crate
//!
//! This crate is allowed to contain other public things if you need, for example
//! traits or functions or ordinary macros.
//!
//! https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack
//!
//! ```rust
//! #[macro_use]
//! extern crate proc_macro_hack;
//!
//! // This is what allows the users to depend on just your
//! // declaration crate rather than both crates.
//! #[allow(unused_imports)]
//! #[macro_use]
//! extern crate demo_hack_impl;
//! #[doc(hidden)]
//! pub use demo_hack_impl::*;
//!
//! proc_macro_expr_decl! {
//! /// Add one to an expression.
//! add_one! => add_one_impl
//! }
//!
//! proc_macro_item_decl! {
//! /// A function that always returns 2.
//! two_fn! => two_fn_impl
//! }
//! # fn main() {}
//! ```
//!
//! ### The implementation crate
//!
//! This crate must contain nothing but procedural macros. Private helper functions
//! and private modules are fine but nothing can be public.
//!
//! https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack-impl
//!
//! ```rust,ignore
//! #[macro_use]
//! extern crate proc_macro_hack;
//!
//! proc_macro_expr_impl! {
//! /// Add one to an expression.
//! pub fn add_one_impl(input: &str) -> String {
//! format!("1 + {}", input)
//! }
//! }
//!
//! proc_macro_item_impl! {
//! /// A function that always returns 2.
//! pub fn two_fn_impl(input: &str) -> String {
//! format!("fn {}() -> u8 {{ 2 }}", input)
//! }
//! }
//! ```
//!
//! Both crates depend on `proc-macro-hack`:
//!
//! ```toml
//! [dependencies]
//! proc-macro-hack = "0.4"
//! ```
//!
//! Additionally, your implementation crate (but not your declaration crate) is a
//! proc macro:
//!
//! ```toml
//! [lib]
//! proc-macro = true
//! ```
//!
//! ## Using procedural macros
//!
//! Users of your crate depend on your declaration crate (not your implementation
//! crate), then use your procedural macros as though it were magic. They even get
//! reasonable error messages if your procedural macro panics.
//!
//! https://github.com/dtolnay/proc-macro-hack/tree/master/example
//!
//! ```rust
//! #[macro_use]
//! extern crate demo_hack;
//!
//! two_fn!(two);
//!
//! fn main() {
//! let nine = add_one!(two()) + add_one!(2 + 3);
//! println!("nine = {}", nine);
//! }
//! ```
//!
//! ---
//!
//! # Expansion of expression macros
//!
//! ```rust,ignore
//! m!(ARGS)
//! ```
//!
//! ... expands to ...
//!
//! ```rust,ignore
//! {
//! #[derive(m_impl)]
//! #[allow(unused)]
//! enum ProcMacroHack {
//! Input = (stringify!(ARGS), 0).1,
//! }
//! proc_macro_call!()
//! }
//! ```
//!
//! ... expands to ...
//!
//! ```rust,ignore
//! {
//! macro_rules! proc_macro_call {
//! () => { RESULT }
//! }
//! proc_macro_call!()
//! }
//! ```
//!
//! ... expands to ...
//!
//! ```rust,ignore
//! {
//! RESULT
//! }
//! ```
//!
//! # Expansion of item macros
//!
//! ```rust,ignore
//! m!(ARGS);
//! ```
//!
//! ... expands to ...
//!
//! ```rust,ignore
//! #[derive(m_impl)]
//! #[allow(unused)]
//! enum ProcMacroHack {
//! Input = (stringify!(ARGS), 0).1,
//! }
//! ```
//!
//! ... expands to ...
//!
//! ```rust,ignore
//! RESULT
//! ```
#![no_std]
// Allow the "unused" #[macro_use] because there is a different un-ignorable
// warning otherwise:
//
// proc macro crates and `#[no_link]` crates have no effect without `#[macro_use]`
#[allow(unused_imports)]
#[macro_use]
extern crate proc_macro_hack_impl;
#[doc(hidden)]
pub use proc_macro_hack_impl::*;
/// Declare a hacky procedural macro that expands to an expression.
///
/// ```rust
/// # #[macro_use] extern crate proc_macro_hack;
/// proc_macro_expr_decl! {
/// /// Add one to an expression.
/// add_one! => add_one_impl
/// }
/// # fn main() {}
/// ```
#[macro_export]
macro_rules! proc_macro_expr_decl {
(#[$attr:meta] $($rest:tt)+) => {
proc_macro_expr_decl_helper!((#[$attr]) $($rest)+);
};
($name:ident ! => $name_impl:ident) => {
proc_macro_expr_decl_helper!(() $name ! => $name_impl);
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! proc_macro_expr_decl_helper {
(($($attrs:tt)*) #[$first:meta] $($rest:tt)+) => {
proc_macro_expr_decl_helper!(($($attrs)* #[$first]) $($rest)+);
};
(($($attrs:tt)*) $name:ident ! => $name_impl:ident) => {
#[derive(ProcMacroHackExpr)]
#[allow(unused, non_camel_case_types)]
$($attrs)*
enum $name {
$name_impl
}
};
(($($attrs:tt)*) $name:ident ! => $name_impl:ident #[$first:meta] $($rest:tt)+) => {
proc_macro_expr_decl_helper!(($($attrs)*) $name ! => $name_impl);
proc_macro_expr_decl_helper!((#[$first]) $($rest)+);
};
}
/// Declare a hacky procedural macro that expands to items.
///
/// ```rust
/// # #[macro_use] extern crate proc_macro_hack;
/// proc_macro_item_decl! {
/// /// A function that always returns 2.
/// two_fn! => two_fn_impl
/// }
/// # fn main() {}
/// ```
#[macro_export]
macro_rules! proc_macro_item_decl {
(#[$attr:meta] $($rest:tt)+) => {
proc_macro_item_decl_helper!((#[$attr]) $($rest)+);
};
($name:ident ! => $name_impl:ident) => {
proc_macro_item_decl_helper!(() $name ! => $name_impl);
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! proc_macro_item_decl_helper {
(($($attrs:tt)*) #[$first:meta] $($rest:tt)+) => {
proc_macro_item_decl_helper!(($($attrs)* #[$first]) $($rest)+);
};
(($($attrs:tt)*) $name:ident ! => $name_impl:ident) => {
#[derive(ProcMacroHackItem)]
#[allow(unused, non_camel_case_types)]
$($attrs)*
enum $name {
$name_impl
}
};
(($($attrs:tt)*) $name:ident ! => $name_impl:ident #[$first:meta] $($rest:tt)+) => {
proc_macro_item_decl_helper!(($($attrs)*) $name ! => $name_impl);
proc_macro_item_decl_helper!((#[$first]) $($rest)+);
};
}
/// Implement a hacky procedural macro that expands to an expression.
///
/// ```rust,ignore
/// proc_macro_expr_impl! {
/// /// Add one to an expression.
/// pub fn add_one_impl(input: &str) -> String {
/// format!("1 + {}", input)
/// }
/// }
/// ```
#[macro_export]
macro_rules! proc_macro_expr_impl {
($(
$( #[$attr:meta] )*
pub fn $func:ident($input:ident: &str) -> String $body:block
)+) => {
$(
mod $func {
extern crate proc_macro;
pub use self::proc_macro::TokenStream;
}
// Parses an input that looks like:
//
// ```
// #[allow(unused)]
// enum ProcMacroHack {
// Input = (stringify!(ARGS), 0).1,
// }
// ```
$( #[$attr] )*
#[proc_macro_derive($func)]
pub fn $func(input: $func::TokenStream) -> $func::TokenStream {
let source = input.to_string();
let mut tokens = source.trim();
for &prefix in &[
"#",
"[",
"allow",
"(",
"unused",
")",
"]",
"enum",
"ProcMacroHack",
"{",
"Input",
"=",
"(",
"stringify",
"!",
"(",
] {
assert!(tokens.starts_with(prefix));
tokens = &tokens[prefix.len()..].trim();
}
for &suffix in &[
"}",
",",
"1",
".",
")",
"0",
",",
")",
] {
if suffix == "," && !tokens.ends_with(suffix) {
continue;
}
assert!(tokens.ends_with(suffix));
tokens = &tokens[..tokens.len() - suffix.len()].trim();
}
fn func($input: &str) -> String $body
format!("
macro_rules! proc_macro_call {{
() => {{
{}
}}
}}
", func(tokens)).parse().unwrap()
}
)+
};
}
/// Implement a hacky procedural macro that expands to items.
///
/// ```rust,ignore
/// proc_macro_item_impl! {
/// /// A function that always returns 2.
/// pub fn two_fn_impl(input: &str) -> String {
/// format!("fn {}() -> u8 {{ 2 }}", input)
/// }
/// }
/// ```
#[macro_export]
macro_rules! proc_macro_item_impl {
($(
$( #[$attr:meta] )*
pub fn $func:ident($input:ident: &str) -> String $body:block
)+) => {
$(
mod $func {
extern crate proc_macro;
pub use self::proc_macro::TokenStream;
}
// Parses an input that looks like:
//
// ```
// #[allow(unused)]
// enum ProcMacroHack {
// Input = (stringify!(ARGS), 0).1,
// }
// ```
$( #[$attr] )*
#[proc_macro_derive($func)]
pub fn $func(input: $func::TokenStream) -> $func::TokenStream {
let source = input.to_string();
let mut tokens = source.trim();
for &prefix in &[
"#",
"[",
"allow",
"(",
"unused",
")",
"]",
"enum",
"ProcMacroHack",
"{",
"Input",
"=",
"(",
"stringify",
"!",
"(",
] {
assert!(tokens.starts_with(prefix));
tokens = &tokens[prefix.len()..].trim();
}
for &suffix in &[
"}",
",",
"1",
".",
")",
"0",
",",
")",
] {
if suffix == "," && !tokens.ends_with(suffix) {
continue;
}
assert!(tokens.ends_with(suffix));
tokens = &tokens[..tokens.len() - suffix.len()].trim();
}
fn func($input: &str) -> String $body
func(tokens).parse().unwrap()
}
)+
};
}