derive_io_macros/

lib.rs

//! Support macros for `derive-io`. This is not intended to be used directly and
//! has no stable API.

use proc_macro::*;

/// `#[derive(Read)]`
#[proc_macro_derive(Read, attributes(read))]
pub fn derive_io_read(input: TokenStream) -> TokenStream {
    generate("derive_io", "derive_io_read", input)
}

/// `#[derive(Write)]`
#[proc_macro_derive(Write, attributes(write))]
pub fn derive_io_write(input: TokenStream) -> TokenStream {
    generate("derive_io", "derive_io_write", input)
}

/// `#[derive(AsyncRead)]`
#[proc_macro_derive(AsyncRead, attributes(read))]
pub fn derive_io_async_read(input: TokenStream) -> TokenStream {
    generate("derive_io", "derive_io_async_read", input)
}

/// `#[derive(AsyncWrite)]`
#[proc_macro_derive(AsyncWrite, attributes(write))]
pub fn derive_io_async_write(input: TokenStream) -> TokenStream {
    generate("derive_io", "derive_io_async_write", input)
}

/// Generates the equivalent of this Rust code as a TokenStream:
///
/// ```nocompile
/// ::ctor::__support::ctor_parse!(#[ctor] fn foo() { ... });
/// ::dtor::__support::dtor_parse!(#[dtor] fn foo() { ... });
/// ```
#[allow(unknown_lints, tail_expr_drop_order)]
fn generate(macro_crate: &str, macro_type: &str, item: TokenStream) -> TokenStream {
    let mut generics = TokenStream::new();
    let mut where_clause = TokenStream::new();
    let mut new_item = TokenStream::new();
    let mut iterator = item.into_iter();

    // Parse out generics and where clause into something easier for macros to digest:
    //  - Generic bounds are moved to where clause, leaving just types/lifetimes
    //  - If a generic has no bounds, we don't add it to the where clause
    let mut in_generics = false;
    let mut generics_ident = false;
    let mut generics_accum = TokenStream::new();
    let mut in_where_clause = false;
    while let Some(token) = iterator.next() {
        match token {
            TokenTree::Punct(p) if p.as_char() == '<' => {
                in_generics = true;
                generics_ident = true;
            }
            TokenTree::Punct(ref p) if p.as_char() == '>' => {
                if in_generics {
                    in_generics = false;
                    if generics_ident {
                        generics.extend(std::mem::take(&mut generics_accum));
                    }
                }
            }
            TokenTree::Punct(ref p) if p.as_char() == ':' => {
                if in_generics {
                    generics_ident = false;
                    generics.extend(generics_accum.clone());
                    where_clause.extend(std::mem::take(&mut generics_accum));
                    where_clause.extend([token]);
                } else if in_where_clause {
                    where_clause.extend([token]);
                } else {
                    new_item.extend([token]);
                }
            }
            TokenTree::Punct(ref p) if p.as_char() == ',' => {
                if in_generics {
                    if generics_ident {
                        generics.extend(std::mem::take(&mut generics_accum));
                        generics.extend([token.clone()]);
                    } else {
                        where_clause.extend([token]);
                    }
                    generics_ident = true;
                } else if in_where_clause {
                    where_clause.extend([token]);
                } else {
                    new_item.extend([token]);
                }
            }
            TokenTree::Ident(l) if l.to_string() == "where" => {
                in_where_clause = true;
            }
            TokenTree::Group(ref p) if p.delimiter() == Delimiter::Brace => {
                new_item.extend([token]);
                break;
            }
            _ => {
                if in_generics {
                    if generics_ident {
                        generics_accum.extend([token]);
                    } else {
                        where_clause.extend([token]);
                    }
                } else if in_where_clause {
                    where_clause.extend([token]);
                } else {
                    new_item.extend([token]);
                }
            }
        }
    }
    new_item.extend(iterator);

    let mut inner = TokenStream::new();
    inner.extend([
        TokenTree::Group(Group::new(Delimiter::Parenthesis, new_item)),
        TokenTree::Group(Group::new(Delimiter::Parenthesis, generics)),
        TokenTree::Group(Group::new(Delimiter::Parenthesis, where_clause)),
    ]);

    let mut invoke = TokenStream::from_iter([
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Alone)),
        TokenTree::Ident(Ident::new(macro_crate, Span::call_site())),
    ]);
    invoke.extend([
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Alone)),
        TokenTree::Ident(Ident::new("__support", Span::call_site())),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Alone)),
        TokenTree::Ident(Ident::new(
            &format!("{}_parse", macro_type),
            Span::call_site(),
        )),
        TokenTree::Punct(Punct::new('!', Spacing::Alone)),
        TokenTree::Group(Group::new(Delimiter::Parenthesis, inner)),
        TokenTree::Punct(Punct::new(';', Spacing::Alone)),
    ]);

    invoke
}

fn expect_any(named: &str, iterator: &mut impl Iterator<Item = TokenTree>) -> TokenTree {
    let next = iterator.next();
    let Some(token) = next else {
        panic!("Expected {} token, got end of stream", named);
    };
    token
}

fn expect_group(named: &str, iterator: &mut impl Iterator<Item = TokenTree>) -> Group {
    let next = iterator.next();
    let Some(TokenTree::Group(group)) = next else {
        panic!("Expected {} group, got {:?}", named, next);
    };
    group
}

fn expect_ident(named: &str, iterator: &mut impl Iterator<Item = TokenTree>) -> Ident {
    let next = iterator.next();
    let Some(TokenTree::Ident(ident)) = next else {
        panic!("Expected {} ident, got {:?}", named, next);
    };
    ident
}

fn expect_literal(named: &str, iterator: &mut impl Iterator<Item = TokenTree>) -> Literal {
    let next = iterator.next();
    if let Some(TokenTree::Group(ref group)) = next {
        if group.delimiter() == Delimiter::None {
            let mut iter = group.stream().into_iter();
            return expect_literal(named, &mut iter);
        }
    }
    let Some(TokenTree::Literal(literal)) = next else {
        panic!("Expected {} literal, got {:?}", named, next);
    };
    literal
}

fn expect_punct(named: char, iterator: &mut impl Iterator<Item = TokenTree>) -> Punct {
    let next = iterator.next();
    let Some(TokenTree::Punct(punct)) = next else {
        panic!("Expected {} punct, got {:?}", named, next);
    };
    if punct.as_char() != named {
        panic!("Expected {} punct, got {:?}", named, punct);
    }
    punct
}

/// Unwrap a grouped meta element to its final group.
fn expect_is_meta(named: &str, mut attr: TokenTree) -> Group {
    let outer = attr.clone();
    while let TokenTree::Group(group) = attr {
        let mut iter = group.clone().stream().into_iter();
        let first = iter
            .next()
            .expect("Expected attr group to have one element");
        if let TokenTree::Ident(_) = first {
            return Group::new(Delimiter::Bracket, group.stream());
        }
        attr = first;
    }
    panic!("Expected meta group {named}, got {outer}");
}

/// [
///   (__next__) (args) expected_attr {on_error}
///   ((attr attr) (item)) ((attr attr) (item))
/// ] -> __next__!((args) (item))
#[proc_macro]
pub fn find_annotated(input: TokenStream) -> TokenStream {
    let mut iterator = input.into_iter();

    let next_macro = expect_group("__next__ macro", &mut iterator);
    let args = expect_group("__next__ arguments", &mut iterator);
    let expected_attr = expect_ident("expected_attr", &mut iterator);
    let on_error = expect_group("on_error", &mut iterator);

    while let Some(token) = iterator.next() {
        let TokenTree::Group(check) = token else {
            panic!("Expected check group");
        };
        let mut iter = check.stream().into_iter();
        let attrs = expect_group("attrs", &mut iter);
        let item = expect_any("item", &mut iter);
        let mut index = 0;
        for attr in attrs.stream().into_iter() {
            let attr = expect_is_meta("attr", attr);
            let first = expect_ident("first attr", &mut attr.clone().stream().into_iter());
            if first.to_string() == expected_attr.to_string() {
                let mut next = next_macro.stream();
                next.extend([
                    TokenTree::Punct(Punct::new('!', Spacing::Alone)),
                    TokenTree::Group(Group::new(
                        Delimiter::Parenthesis,
                        TokenStream::from_iter([
                            TokenTree::Group(args),
                            TokenTree::Literal(Literal::usize_unsuffixed(index)),
                            TokenTree::Group(attr),
                            item,
                        ]),
                    )),
                    TokenTree::Punct(Punct::new(';', Spacing::Alone)),
                ]);
                return next;
            }
            index += 1;
        }
    }

    on_error.stream()
}

/// [(__next__) (args) expected_attr {on_error}
///  ( (id) (([attr] [attr]) (item)) (([attr] [attr]) (item)) )
///  ( (id) (([attr] [attr]) (item)) (([attr] [attr]) (item)) )
/// ] -> __next__!((args) ((id) (item)))
#[proc_macro]
pub fn find_annotated_multi(input: TokenStream) -> TokenStream {
    let mut iterator = input.into_iter();

    let next_macro = expect_group("__next__ macro", &mut iterator);
    let args = expect_group("__next__ arguments", &mut iterator);
    let expected_attr = expect_ident("expected_attr", &mut iterator);
    let on_error = expect_group("on_error", &mut iterator);
    let mut output = TokenStream::new();

    'outer: while let Some(token) = iterator.next() {
        let TokenTree::Group(id) = token else {
            panic!("Expected id group");
        };
        let mut iter = id.stream().into_iter();
        let id = expect_group("id", &mut iter);
        let mut index = 0;
        while let Some(token) = iter.next() {
            let TokenTree::Group(check) = token else {
                panic!("Expected check group");
            };
            let mut iter = check.stream().into_iter();
            let attrs = expect_group("attrs", &mut iter);
            let item = expect_any("item", &mut iter);
            for attr in attrs.stream().into_iter() {
                let attr = expect_is_meta("attr", attr);
                let first = expect_ident("first attr", &mut attr.clone().stream().into_iter());
                if first.to_string() == expected_attr.to_string() {
                    output.extend([TokenTree::Group(Group::new(
                        Delimiter::Parenthesis,
                        TokenStream::from_iter([
                            TokenTree::Group(id.clone()),
                            TokenTree::Literal(Literal::usize_unsuffixed(index)),
                            TokenTree::Group(attr),
                            item.clone(),
                        ]),
                    ))]);
                    continue 'outer;
                }
            }
            index += 1;
        }
        return on_error.stream();
    }

    let mut next = next_macro.stream();
    next.extend([
        TokenTree::Punct(Punct::new('!', Spacing::Alone)),
        TokenTree::Group(Group::new(
            Delimiter::Parenthesis,
            TokenStream::from_iter([
                TokenTree::Group(args),
                TokenTree::Group(Group::new(Delimiter::Parenthesis, output)),
            ]),
        )),
        TokenTree::Punct(Punct::new(';', Spacing::Alone)),
    ]);
    next
}

/// [prefix count repeated suffix] -> prefix (repeated*count suffix)
#[proc_macro]
pub fn repeat_in_parenthesis(input: TokenStream) -> TokenStream {
    let mut iterator = input.into_iter();
    let prefix = expect_group("prefix", &mut iterator);
    let count = expect_literal("count", &mut iterator);
    let count =
        usize::from_str_radix(&count.to_string(), 10).expect("Expected count to be a number");
    let repeated = expect_group("repeated", &mut iterator);
    let suffix = expect_group("suffix", &mut iterator);
    let mut repeat = TokenStream::new();
    for _ in 0..count {
        repeat.extend(repeated.clone().stream());
    }
    repeat.extend(suffix.stream());
    let mut output = TokenStream::new();
    output.extend(prefix.stream());
    output.extend([TokenTree::Group(Group::new(Delimiter::Parenthesis, repeat))]);
    output
}

// needle haystack(key=value,key=value) default -> extracted OR default
#[proc_macro]
pub fn extract_meta(input: TokenStream) -> TokenStream {
    let mut iterator = input.into_iter();
    let needle = expect_ident("needle", &mut iterator);
    let haystack = expect_group("haystack", &mut iterator);
    let default = expect_group("default", &mut iterator);

    let mut haystack = haystack.stream().into_iter();

    loop {
        let attr = haystack.next();
        if let Some(TokenTree::Group(ref group)) = attr {
            haystack = group.stream().into_iter();
            continue;
        }
        break;
    }

    loop {
        let key = haystack.next();
        if let Some(TokenTree::Group(ref group)) = key {
            haystack = group.stream().into_iter();
            continue;
        }
        let Some(key) = key else {
            break;
        };
        expect_punct('=', &mut haystack);
        let value = expect_ident("value", &mut haystack);

        if key.to_string() == needle.to_string() {
            return TokenStream::from_iter([TokenTree::Ident(value)]);
        }

        if haystack.next().is_none() {
            break;
        }
    }

    default.stream()
}