blob: 238e54ec170db4614604c57e4473e2f14d932bed [file] [log] [blame]
//! As of Rust 1.30, the language supports user-defined function-like procedural
//! macros. However these can only be invoked in item position, not in
//! statements or expressions.
//!
//! This crate implements an alternative type of procedural macro that can be
//! invoked in statement or expression position.
//!
//! # Defining procedural macros
//!
//! Two crates are required to define a procedural macro.
//!
//! ## The implementation crate
//!
//! This crate must contain nothing but procedural macros. Private helper
//! functions and private modules are fine but nothing can be public.
//!
//! [> example of an implementation crate][demo-hack-impl]
//!
//! Just like you would use a #\[proc_macro\] attribute to define a natively
//! supported procedural macro, use proc-macro-hack's #\[proc_macro_hack\]
//! attribute to define a procedural macro that works in expression position.
//! The function signature is the same as for ordinary function-like procedural
//! macros.
//!
//! ```rust
//! extern crate proc_macro;
//! extern crate proc_macro_hack;
//! extern crate quote;
//! extern crate syn;
//!
//! use proc_macro::TokenStream;
//! use proc_macro_hack::proc_macro_hack;
//! use quote::quote;
//! use syn::{parse_macro_input, Expr};
//!
//! /// Add one to an expression.
//! # const IGNORE: &str = stringify! {
//! #[proc_macro_hack]
//! # };
//! pub fn add_one(input: TokenStream) -> TokenStream {
//! let expr = parse_macro_input!(input as Expr);
//! TokenStream::from(quote! {
//! 1 + (#expr)
//! })
//! }
//! #
//! # fn main() {}
//! ```
//!
//! ## The declaration crate
//!
//! This crate is allowed to contain other public things if you need, for
//! example traits or functions or ordinary macros.
//!
//! [> example of a declaration crate][demo-hack]
//!
//! Within the declaration crate there needs to be a re-export of your
//! procedural macro from the implementation crate. The re-export also carries a
//! \#\[proc_macro_hack\] attribute.
//!
//! ```rust
//! extern crate demo_hack_impl;
//! extern crate proc_macro_hack;
//!
//! use proc_macro_hack::proc_macro_hack;
//!
//! /// Add one to an expression.
//! #[proc_macro_hack]
//! pub use demo_hack_impl::add_one;
//! #
//! # fn main() {}
//! ```
//!
//! Both crates depend on `proc-macro-hack`:
//!
//! ```toml
//! [dependencies]
//! proc-macro-hack = "0.5"
//! ```
//!
//! Additionally, your implementation crate (but not your declaration crate) is
//! a proc macro crate:
//!
//! ```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 usual.
//!
//! [> example of a downstream crate][example]
//!
//! ```rust
//! extern crate demo_hack;
//! use demo_hack::add_one;
//!
//! fn main() {
//! let two = 2;
//! let nine = add_one!(two) + add_one!(2 + 3);
//! println!("nine = {}", nine);
//! }
//! ```
//!
//! [demo-hack-impl]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack-impl
//! [demo-hack]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack
//! [example]: https://github.com/dtolnay/proc-macro-hack/tree/master/example
#![recursion_limit = "512"]
#![cfg_attr(feature = "cargo-clippy", allow(renamed_and_removed_lints))]
#![cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]
extern crate proc_macro;
extern crate proc_macro2;
extern crate quote;
extern crate syn;
use std::fmt::Write;
use proc_macro2::{Span, TokenStream, TokenTree};
use quote::{quote, ToTokens};
use syn::parse::{Parse, ParseStream, Result};
use syn::{braced, bracketed, parenthesized, parse_macro_input, token, Ident, Token};
type Visibility = Option<Token![pub]>;
enum Input {
Export(Export),
Define(Define),
}
// pub use demo_hack_impl::{m1, m2 as qrst};
struct Export {
attrs: TokenStream,
vis: Visibility,
from: Ident,
macros: Vec<Macro>,
}
// pub fn m1(input: TokenStream) -> TokenStream { ... }
struct Define {
attrs: TokenStream,
name: Ident,
body: TokenStream,
}
struct Macro {
name: Ident,
export_as: Ident,
}
impl Parse for Input {
fn parse(input: ParseStream) -> Result<Self> {
let ahead = input.fork();
parse_attributes(&ahead)?;
ahead.parse::<Visibility>()?;
if ahead.peek(Token![use]) {
input.parse().map(Input::Export)
} else if ahead.peek(Token![fn]) {
input.parse().map(Input::Define)
} else {
Err(input.error("unexpected input to #[proc_macro_hack]"))
}
}
}
impl Parse for Export {
fn parse(input: ParseStream) -> Result<Self> {
let attrs = input.call(parse_attributes)?;
let vis: Visibility = input.parse()?;
input.parse::<Token![use]>()?;
let from: Ident = input.parse()?;
input.parse::<Token![::]>()?;
let mut macros = Vec::new();
if input.peek(token::Brace) {
let content;
braced!(content in input);
loop {
macros.push(content.parse()?);
if content.is_empty() {
break;
}
content.parse::<Token![,]>()?;
if content.is_empty() {
break;
}
}
} else {
macros.push(input.parse()?);
}
input.parse::<Token![;]>()?;
Ok(Export { attrs, vis, from, macros })
}
}
impl Parse for Define {
fn parse(input: ParseStream) -> Result<Self> {
let attrs = input.call(parse_attributes)?;
let vis: Visibility = input.parse()?;
if vis.is_none() {
return Err(input.error("functions tagged with `#[proc_macro_hack]` must be `pub`"));
}
input.parse::<Token![fn]>()?;
let name: Ident = input.parse()?;
let body: TokenStream = input.parse()?;
Ok(Define { attrs, name, body })
}
}
impl Parse for Macro {
fn parse(input: ParseStream) -> Result<Self> {
let name: Ident = input.parse()?;
let renamed: Option<Token![as]> = input.parse()?;
let export_as = if renamed.is_some() {
input.parse()?
} else {
name.clone()
};
Ok(Macro { name, export_as })
}
}
fn parse_attributes(input: ParseStream) -> Result<TokenStream> {
let mut attrs = TokenStream::new();
while input.peek(Token![#]) {
let pound: Token![#] = input.parse()?;
pound.to_tokens(&mut attrs);
let content;
let bracket_token = bracketed!(content in input);
let content: TokenStream = content.parse()?;
bracket_token.surround(&mut attrs, |tokens| content.to_tokens(tokens));
}
Ok(attrs)
}
#[proc_macro_attribute]
pub fn proc_macro_hack(
args: proc_macro::TokenStream,
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
proc_macro::TokenStream::from(match parse_macro_input!(input) {
Input::Export(export) => {
let args = parse_macro_input!(args as ExportArgs);
expand_export(export, args)
}
Input::Define(define) => {
parse_macro_input!(args as DefineArgs);
expand_define(define)
}
})
}
mod kw {
syn::custom_keyword!(support_nested);
}
struct ExportArgs {
support_nested: bool,
}
impl Parse for ExportArgs {
fn parse(input: ParseStream) -> Result<Self> {
Ok(ExportArgs {
support_nested: input.parse::<Option<kw::support_nested>>()?.is_some(),
})
}
}
struct DefineArgs;
impl Parse for DefineArgs {
fn parse(_input: ParseStream) -> Result<Self> {
Ok(DefineArgs)
}
}
struct EnumHack {
token_stream: TokenStream,
}
impl Parse for EnumHack {
fn parse(input: ParseStream) -> Result<Self> {
input.parse::<Token![enum]>()?;
input.parse::<Ident>()?;
let braces;
braced!(braces in input);
braces.parse::<Ident>()?;
braces.parse::<Token![=]>()?;
let parens;
parenthesized!(parens in braces);
parens.parse::<Ident>()?;
parens.parse::<Token![!]>()?;
let inner;
braced!(inner in parens);
let token_stream: TokenStream = inner.parse()?;
parens.parse::<Token![,]>()?;
parens.parse::<TokenTree>()?;
braces.parse::<Token![.]>()?;
braces.parse::<TokenTree>()?;
braces.parse::<Token![,]>()?;
Ok(EnumHack { token_stream })
}
}
#[doc(hidden)]
#[proc_macro_derive(ProcMacroHack)]
pub fn enum_hack(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let inner = parse_macro_input!(input as EnumHack);
proc_macro::TokenStream::from(inner.token_stream)
}
fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
let dummy = dummy_name_for_export(&export);
let attrs = export.attrs;
let vis = export.vis;
let macro_export = match vis {
Some(_) => quote!(#[macro_export]),
None => quote!(),
};
let crate_prefix = match vis {
Some(_) => quote!($crate::),
None => quote!(),
};
let enum_variant = if args.support_nested {
quote!(Nested)
} else {
quote!(Value)
};
let from = export.from;
let rules = export
.macros
.into_iter()
.map(|Macro { name, export_as }| {
let actual_name = actual_proc_macro_name(&name);
let dispatch = dispatch_macro_name(&name);
let export_dispatch = if args.support_nested {
Some(quote! {
#[doc(hidden)]
#vis use proc_macro_nested::dispatch as #dispatch;
})
} else {
None
};
let proc_macro_call = if args.support_nested {
quote! {
#crate_prefix #dispatch! { ($($proc_macro)*) }
}
} else {
quote! {
proc_macro_call!()
}
};
quote! {
#[doc(hidden)]
#vis use #from::#actual_name;
#export_dispatch
#attrs
#macro_export
macro_rules! #export_as {
($($proc_macro:tt)*) => {{
#[derive(#crate_prefix #actual_name)]
enum ProcMacroHack {
#enum_variant = (stringify! { $($proc_macro)* }, 0).1,
}
#proc_macro_call
}};
}
}
})
.collect();
wrap_in_enum_hack(dummy, rules)
}
fn expand_define(define: Define) -> TokenStream {
let attrs = define.attrs;
let name = define.name;
let dummy = actual_proc_macro_name(&name);
let body = define.body;
quote! {
mod #dummy {
extern crate proc_macro;
pub use self::proc_macro::*;
}
#attrs
#[proc_macro_derive(#dummy)]
pub fn #dummy(input: #dummy::TokenStream) -> #dummy::TokenStream {
use std::iter::FromIterator;
let mut iter = input.into_iter();
iter.next().unwrap(); // `enum`
iter.next().unwrap(); // `ProcMacroHack`
let mut braces = match iter.next().unwrap() {
#dummy::TokenTree::Group(group) => group.stream().into_iter(),
_ => unimplemented!(),
};
let variant = braces.next().unwrap(); // `Value` or `Nested`
let support_nested = variant.to_string() == "Nested";
braces.next().unwrap(); // `=`
let mut parens = match braces.next().unwrap() {
#dummy::TokenTree::Group(group) => group.stream().into_iter(),
_ => unimplemented!(),
};
parens.next().unwrap(); // `stringify`
parens.next().unwrap(); // `!`
let inner = match parens.next().unwrap() {
#dummy::TokenTree::Group(group) => group.stream(),
_ => unimplemented!(),
};
let output: #dummy::TokenStream = #name(inner.clone());
fn count_bangs(input: #dummy::TokenStream) -> usize {
let mut count = 0;
for token in input {
match token {
#dummy::TokenTree::Punct(punct) => {
if punct.as_char() == '!' {
count += 1;
}
}
#dummy::TokenTree::Group(group) => {
count += count_bangs(group.stream());
}
_ => {}
}
}
count
}
// macro_rules! proc_macro_call {
// () => { #output }
// }
#dummy::TokenStream::from_iter(vec![
#dummy::TokenTree::Ident(
#dummy::Ident::new("macro_rules", #dummy::Span::call_site()),
),
#dummy::TokenTree::Punct(
#dummy::Punct::new('!', #dummy::Spacing::Alone),
),
#dummy::TokenTree::Ident(
#dummy::Ident::new(
&if support_nested {
format!("proc_macro_call_{}", count_bangs(inner))
} else {
String::from("proc_macro_call")
},
#dummy::Span::call_site(),
),
),
#dummy::TokenTree::Group(
#dummy::Group::new(#dummy::Delimiter::Brace, #dummy::TokenStream::from_iter(vec![
#dummy::TokenTree::Group(
#dummy::Group::new(#dummy::Delimiter::Parenthesis, #dummy::TokenStream::new()),
),
#dummy::TokenTree::Punct(
#dummy::Punct::new('=', #dummy::Spacing::Joint),
),
#dummy::TokenTree::Punct(
#dummy::Punct::new('>', #dummy::Spacing::Alone),
),
#dummy::TokenTree::Group(
#dummy::Group::new(#dummy::Delimiter::Brace, output),
),
])),
),
])
}
fn #name #body
}
}
fn actual_proc_macro_name(conceptual: &Ident) -> Ident {
let actual_name = format!("proc_macro_hack_{}", conceptual);
Ident::new(&actual_name, Span::call_site())
}
fn dispatch_macro_name(conceptual: &Ident) -> Ident {
let dispatch = format!("proc_macro_call_{}", conceptual);
Ident::new(&dispatch, Span::call_site())
}
fn dummy_name_for_export(export: &Export) -> String {
let mut dummy = String::new();
write!(dummy, "_{}{}", export.from.to_string().len(), export.from).unwrap();
for m in &export.macros {
write!(dummy, "_{}{}", m.name.to_string().len(), m.name).unwrap();
}
dummy
}
fn wrap_in_enum_hack(dummy: String, inner: TokenStream) -> TokenStream {
let dummy = Ident::new(&dummy, Span::call_site());
quote! {
#[derive(proc_macro_hack::ProcMacroHack)]
enum #dummy {
Value = (stringify! { #inner }, 0).1,
}
}
}