//! Note:As of Rust 1.45 this crate is superseded by native support
//! for #[proc_macro] in expression position. Only consider using this crate if
//! you care about supporting compilers between 1.31 and 1.45.
//!
//!
//! Since 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.
//!
//! ```
//! # extern crate proc_macro;
//! #
//! use proc_macro::TokenStream;
//! use proc_macro_hack::proc_macro_hack;
//! use quote::quote;
//! use syn::{parse_macro_input, Expr};
//!
//! # 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.
//!
//! ```
//! use proc_macro_hack::proc_macro_hack;
//!
//! /// Add one to an expression.
//! ///
//! /// (Documentation goes here on the re-export, not in the other crate.)
//! #[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]
//!
//! ```
//! 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
//!
//! # Limitations
//!
//! - Only proc macros in expression position are supported. Proc macros in
//! pattern position ([#20]) are not supported.
//!
//! - By default, nested invocations are not supported i.e. the code emitted by
//! a proc-macro-hack macro invocation cannot contain recursive calls to the
//! same proc-macro-hack macro nor calls to any other proc-macro-hack macros.
//! Use [`proc-macro-nested`] if you require support for nested invocations.
//!
//! - By default, hygiene is structured such that the expanded code can't refer
//! to local variables other than those passed by name somewhere in the macro
//! input. If your macro must refer to *local* variables that don't get named
//! in the macro input, use `#[proc_macro_hack(fake_call_site)]` on the
//! re-export in your declaration crate. *Most macros won't need this.*
//!
//! - On compilers that are new enough to natively support proc macros in
//! expression position, proc-macro-hack does not automatically use that
//! support, since the hygiene can be subtly different between the two
//! implementations. To opt in to compiling your macro to native
//! `#[proc_macro]` on sufficiently new compilers, use
//! `#[proc_macro_hack(only_hack_old_rustc)]` on the re-export in your
//! declaration crate.
//!
//! [#10]: https://github.com/dtolnay/proc-macro-hack/issues/10
//! [#20]: https://github.com/dtolnay/proc-macro-hack/issues/20
//! [`proc-macro-nested`]: https://docs.rs/proc-macro-nested
#![recursion_limit = "512"]
#![allow(
clippy::doc_markdown,
clippy::manual_strip,
clippy::module_name_repetitions,
clippy::needless_doctest_main,
clippy::needless_pass_by_value,
clippy::too_many_lines,
clippy::toplevel_ref_arg
)]
extern crate proc_macro;
#[macro_use]
mod quote;
mod error;
mod iter;
mod parse;
use crate::error::{compile_error, Error};
use crate::iter::Iter;
use crate::parse::{
parse_define_args, parse_enum_hack, parse_export_args, parse_fake_call_site, parse_input,
};
use proc_macro::{Ident, Punct, Spacing, Span, TokenStream, TokenTree};
use std::fmt::Write;
type Visibility = Option;
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,
}
// pub fn m1(input: TokenStream) -> TokenStream { ... }
struct Define {
attrs: TokenStream,
name: Ident,
body: TokenStream,
}
struct Macro {
name: Ident,
export_as: Ident,
}
#[proc_macro_attribute]
pub fn proc_macro_hack(args: TokenStream, input: TokenStream) -> TokenStream {
let ref mut args = iter::new(args);
let ref mut input = iter::new(input);
expand_proc_macro_hack(args, input).unwrap_or_else(compile_error)
}
fn expand_proc_macro_hack(args: Iter, input: Iter) -> Result {
match parse_input(input)? {
Input::Export(export) => {
let args = parse_export_args(args)?;
Ok(expand_export(export, args))
}
Input::Define(define) => {
parse_define_args(args)?;
Ok(expand_define(define))
}
}
}
#[doc(hidden)]
#[proc_macro_derive(ProcMacroHack)]
pub fn enum_hack(input: TokenStream) -> TokenStream {
let ref mut input = iter::new(input);
parse_enum_hack(input).unwrap_or_else(compile_error)
}
struct FakeCallSite {
derive: Ident,
rest: TokenStream,
}
#[doc(hidden)]
#[proc_macro_attribute]
pub fn fake_call_site(args: TokenStream, input: TokenStream) -> TokenStream {
let ref mut args = iter::new(args);
let ref mut input = iter::new(input);
expand_fake_call_site(args, input).unwrap_or_else(compile_error)
}
fn expand_fake_call_site(args: Iter, input: Iter) -> Result {
let span = match args.next() {
Some(token) => token.span(),
None => return Ok(input.collect()),
};
let input = parse_fake_call_site(input)?;
let mut derive = input.derive;
derive.set_span(span);
let rest = input.rest;
Ok(quote! {
#[derive(#derive)]
#rest
})
}
struct ExportArgs {
support_nested: bool,
internal_macro_calls: u16,
fake_call_site: bool,
only_hack_old_rustc: bool,
}
fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
if args.only_hack_old_rustc && cfg!(not(need_proc_macro_hack)) {
return expand_export_nohack(export);
}
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 = vis.as_ref().map(|_| quote!($crate::));
let enum_variant = if args.support_nested {
if args.internal_macro_calls == 0 {
Ident::new("Nested", Span::call_site())
} else {
let name = format!("Nested{}", args.internal_macro_calls);
Ident::new(&name, Span::call_site())
}
} else {
Ident::new("Value", Span::call_site())
};
let from = export.from;
let mut actual_names = TokenStream::new();
let mut export_dispatch = TokenStream::new();
let mut export_call_site = TokenStream::new();
let mut macro_rules = TokenStream::new();
for Macro { name, export_as } in &export.macros {
let hacked = hacked_proc_macro_name(name);
let dispatch = dispatch_macro_name(name);
let call_site = call_site_macro_name(name);
if !actual_names.is_empty() {
actual_names.extend(quote!(,));
}
actual_names.extend(quote!(#hacked));
if !export_dispatch.is_empty() {
export_dispatch.extend(quote!(,));
}
export_dispatch.extend(quote!(dispatch as #dispatch));
if !export_call_site.is_empty() {
export_call_site.extend(quote!(,));
}
export_call_site.extend(quote!(fake_call_site as #call_site));
let do_derive = if !args.fake_call_site {
quote! {
#[derive(#crate_prefix #hacked)]
}
} else if crate_prefix.is_some() {
quote! {
use #crate_prefix #hacked;
#[#crate_prefix #call_site ($($proc_macro)*)]
#[derive(#hacked)]
}
} else {
quote! {
#[#call_site ($($proc_macro)*)]
#[derive(#hacked)]
}
};
let proc_macro_call = if args.support_nested {
let extra_bangs = (0..args.internal_macro_calls)
.map(|_| TokenTree::Punct(Punct::new('!', Spacing::Alone)))
.collect::();
quote! {
#crate_prefix #dispatch! { ($($proc_macro)*) #extra_bangs }
}
} else {
quote! {
proc_macro_call!()
}
};
macro_rules.extend(quote! {
#attrs
#macro_export
macro_rules! #export_as {
($($proc_macro:tt)*) => {{
#do_derive
#[allow(dead_code)]
enum ProcMacroHack {
#enum_variant = (stringify! { $($proc_macro)* }, 0).1,
}
#proc_macro_call
}};
}
});
}
if export.macros.len() != 1 {
export_dispatch = quote!({#export_dispatch});
export_call_site = quote!({#export_call_site});
actual_names = quote!({#actual_names});
}
let export_dispatch = if args.support_nested {
quote! {
#[doc(hidden)]
#vis use proc_macro_nested::#export_dispatch;
}
} else {
quote!()
};
let export_call_site = if args.fake_call_site {
quote! {
#[doc(hidden)]
#vis use proc_macro_hack::#export_call_site;
}
} else {
quote!()
};
let expanded = quote! {
#[doc(hidden)]
#vis use #from::#actual_names;
#export_dispatch
#export_call_site
#macro_rules
};
wrap_in_enum_hack(dummy, expanded)
}
fn expand_export_nohack(export: Export) -> TokenStream {
let attrs = export.attrs;
let vis = export.vis;
let from = export.from;
let mut names = TokenStream::new();
for Macro { name, export_as } in &export.macros {
let pub_name = pub_proc_macro_name(name);
if !names.is_empty() {
names.extend(quote!(,));
}
names.extend(quote!(#pub_name as #export_as));
}
if export.macros.len() != 1 {
names = quote!({#names});
}
quote! {
#attrs
#vis use #from::#names;
}
}
fn expand_define(define: Define) -> TokenStream {
let attrs = define.attrs;
let name = define.name;
let pub_name = pub_proc_macro_name(&name);
let hacked = hacked_proc_macro_name(&name);
let body = define.body;
quote! {
mod #pub_name {
extern crate proc_macro;
pub use self::proc_macro::*;
}
#attrs
#[doc(hidden)]
#[proc_macro_derive(#hacked)]
pub fn #hacked(input: #pub_name::TokenStream) -> #pub_name::TokenStream {
use std::iter::FromIterator;
let mut iter = input.into_iter();
iter.next().unwrap(); // `enum`
iter.next().unwrap(); // `ProcMacroHack`
iter.next().unwrap(); // `#`
iter.next().unwrap(); // `[allow(dead_code)]`
let mut braces = match iter.next().unwrap() {
#pub_name::TokenTree::Group(group) => group.stream().into_iter(),
_ => unimplemented!(),
};
let variant = braces.next().unwrap(); // `Value` or `Nested`
let varname = variant.to_string();
let support_nested = varname.starts_with("Nested");
braces.next().unwrap(); // `=`
let mut parens = match braces.next().unwrap() {
#pub_name::TokenTree::Group(group) => group.stream().into_iter(),
_ => unimplemented!(),
};
parens.next().unwrap(); // `stringify`
parens.next().unwrap(); // `!`
let inner = match parens.next().unwrap() {
#pub_name::TokenTree::Group(group) => group.stream(),
_ => unimplemented!(),
};
let output: #pub_name::TokenStream = #name(inner.clone());
fn count_bangs(input: #pub_name::TokenStream) -> usize {
let mut count = 0;
for token in input {
match token {
#pub_name::TokenTree::Punct(punct) => {
if punct.as_char() == '!' {
count += 1;
}
}
#pub_name::TokenTree::Group(group) => {
count += count_bangs(group.stream());
}
_ => {}
}
}
count
}
// macro_rules! proc_macro_call {
// () => { #output }
// }
#pub_name::TokenStream::from_iter(vec![
#pub_name::TokenTree::Ident(
#pub_name::Ident::new("macro_rules", #pub_name::Span::call_site()),
),
#pub_name::TokenTree::Punct(
#pub_name::Punct::new('!', #pub_name::Spacing::Alone),
),
#pub_name::TokenTree::Ident(
#pub_name::Ident::new(
&if support_nested {
let extra_bangs = if varname == "Nested" {
0
} else {
varname["Nested".len()..].parse().unwrap()
};
format!("proc_macro_call_{}", extra_bangs + count_bangs(inner))
} else {
String::from("proc_macro_call")
},
#pub_name::Span::call_site(),
),
),
#pub_name::TokenTree::Group(
#pub_name::Group::new(#pub_name::Delimiter::Brace, #pub_name::TokenStream::from_iter(vec![
#pub_name::TokenTree::Group(
#pub_name::Group::new(#pub_name::Delimiter::Parenthesis, #pub_name::TokenStream::new()),
),
#pub_name::TokenTree::Punct(
#pub_name::Punct::new('=', #pub_name::Spacing::Joint),
),
#pub_name::TokenTree::Punct(
#pub_name::Punct::new('>', #pub_name::Spacing::Alone),
),
#pub_name::TokenTree::Group(
#pub_name::Group::new(#pub_name::Delimiter::Brace, output),
),
])),
),
])
}
#attrs
#[proc_macro]
pub fn #pub_name(input: #pub_name::TokenStream) -> #pub_name::TokenStream {
#name(input)
}
fn #name #body
}
}
fn pub_proc_macro_name(conceptual: &Ident) -> Ident {
Ident::new(
&format!("proc_macro_hack_{}", conceptual),
conceptual.span(),
)
}
fn hacked_proc_macro_name(conceptual: &Ident) -> Ident {
Ident::new(
&format!("_proc_macro_hack_{}", conceptual),
conceptual.span(),
)
}
fn dispatch_macro_name(conceptual: &Ident) -> Ident {
Ident::new(
&format!("proc_macro_call_{}", conceptual),
conceptual.span(),
)
}
fn call_site_macro_name(conceptual: &Ident) -> Ident {
Ident::new(
&format!("proc_macro_fake_call_site_{}", conceptual),
conceptual.span(),
)
}
fn dummy_name_for_export(export: &Export) -> String {
let mut dummy = String::new();
let from = unraw(&export.from).to_string();
write!(dummy, "_{}{}", from.len(), from).unwrap();
for m in &export.macros {
let name = unraw(&m.name).to_string();
write!(dummy, "_{}{}", name.len(), name).unwrap();
}
dummy
}
fn unraw(ident: &Ident) -> Ident {
let string = ident.to_string();
if string.starts_with("r#") {
Ident::new(&string[2..], ident.span())
} else {
ident.clone()
}
}
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,
}
}
}