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#![forbid(unsafe_code)]
#![warn(unused_results)]
use std::iter;
use std::result;
use proc_macro::Delimiter;
use proc_macro::Group;
use proc_macro::Ident;
use proc_macro::Literal;
use proc_macro::Punct;
use proc_macro::Spacing;
use proc_macro::Span;
use proc_macro::TokenStream;
use proc_macro::TokenTree;
trait TokenStreamExt {
fn push<T>(&mut self, token: T)
where
T: Into<TokenTree>;
}
impl TokenStreamExt for TokenStream {
fn push<T>(&mut self, token: T)
where
T: Into<TokenTree>,
{
self.extend(iter::once(token.into()));
}
}
fn macro_path(module: &str, name: &str) -> impl Iterator<Item = TokenTree> {
[
Punct::new(':', Spacing::Joint).into(),
Punct::new(':', Spacing::Alone).into(),
Ident::new(module, Span::call_site()).into(),
Punct::new(':', Spacing::Joint).into(),
Punct::new(':', Spacing::Alone).into(),
Ident::new(name, Span::call_site()).into(),
Punct::new('!', Spacing::Alone).into(),
]
.into_iter()
}
#[derive(Copy, Clone)]
struct Error {
start: Span,
end: Span,
message: &'static str,
}
impl Error {
const fn new(span: Span, message: &'static str) -> Self {
Self {
start: span,
end: span,
message,
}
}
fn new_spanned<T>(tokens: T, message: &'static str) -> Self
where
T: Into<TokenStream>,
{
let mut tokens = tokens.into().into_iter();
let start = tokens
.next()
.map(|x| x.span())
.unwrap_or_else(Span::call_site);
Self {
start,
end: tokens.last().map(|x| x.span()).unwrap_or(start),
message,
}
}
fn to_compile_error(self) -> TokenStream {
let mut result: TokenStream = macro_path("std", "compile_error")
.map(|mut token| {
token.set_span(self.start);
token
})
.collect();
let mut literal = Literal::string(self.message);
literal.set_span(self.end);
let mut group =
Group::new(Delimiter::Brace, TokenTree::Literal(literal).into());
group.set_span(self.end);
result.push(group);
result
}
}
type Result<T> = result::Result<T, Error>;
fn take_signature<I>(mut tokens: &mut I) -> Result<TokenStream>
where
I: Iterator<Item = TokenTree>,
{
let mut signature = TokenStream::new();
for token in &mut tokens {
let matched =
matches!(&token, TokenTree::Ident(x) if x.to_string() == "fn");
signature.push(token);
if matched {
break;
}
}
let name = tokens.next().ok_or_else(|| {
Error::new(
Span::call_site(),
"`#[quit::main]` can only be attached to functions",
)
})?;
if !matches!(&name, TokenTree::Ident(x) if x.to_string() == "main") {
return Err(Error::new_spanned(
name,
"`#[quit::main]` can only be attached to `main`",
));
}
signature.push(name);
Ok(signature)
}
#[proc_macro_attribute]
pub fn main(args: TokenStream, item: TokenStream) -> TokenStream {
if !args.is_empty() {
return Error::new_spanned(args, "arguments are not accepted")
.to_compile_error();
}
let mut item = item.into_iter();
take_signature(&mut item)
.map(|signature| {
macro_path("quit", "__main")
.chain(iter::once(
Group::new(
Delimiter::Brace,
iter::once(
Group::new(Delimiter::Parenthesis, signature)
.into(),
)
.chain(item)
.collect(),
)
.into(),
))
.collect()
})
.unwrap_or_else(Error::to_compile_error)
}