proconio-derive 0.2.1

// Copyright 2019 statiolake <statiolake@gmail.com>
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be copied, modified, or
// distributed except according to those terms.

#![recursion_limit = "128"]
#![allow(clippy::needless_doctest_main)]

//! Macros to easily derive `Readable` and make stdout faster.
//!
//! proconio_derive provides two procedural macros (attributes): `derive_readable` and `fastout`.
//!
//! # Examples for `#[derive_readable]`
//!
//! ```
//! # extern crate proconio;
//! # extern crate proconio_derive;
//! use proconio::input;
//! # use proconio::source::auto::AutoSource;
//! use proconio_derive::derive_readable;
//!
//! // Unit struct can derive readable.  This generates a no-op for the reading.  Not ignoring
//! // the read value, but simply skip reading process.  You cannot use it to discard the input.
//! #[derive_readable]
//! #[derive(PartialEq, Debug)]
//! struct Weight;
//!
//! #[derive_readable]
//! #[derive(PartialEq, Debug)]
//! struct Cost(i32);
//!
//! #[derive_readable]
//! #[derive(Debug)]
//! struct Edge {
//!     from: usize,
//!     to: proconio::marker::Usize1, // The real Edge::to has type usize.
//!     weight: Weight,
//!     cost: Cost,
//! }
//!
//! fn main() {
//! #   let source = AutoSource::from("12 32 35");
//!     input! {
//! #       from source,
//!         edge: Edge,
//!     }
//!
//!     // if you enter "12 32 35" to the stdin, the values are as follows.
//!     assert_eq!(edge.from, 12);
//!     assert_eq!(edge.to, 31);
//!     assert_eq!(edge.weight, Weight);
//!     assert_eq!(edge.cost, Cost(35));
//! }
//! ```
//!
//! # Examples for `#[fastout]`
//!
//! ```
//! use proconio_derive::fastout;
//!
//! #[fastout]
//! fn main() {
//!     print!("{}{}, ", 'h', "ello"); // "hello"       (no newline)
//!     println!("{}!", "world");      // "world!\n"
//!     println!("{}", 123456789);     // "123456789\n"
//! }
//! ```
extern crate proc_macro;

use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
use proc_macro2::{Span as Span2, TokenStream as TokenStream2};
use quote::ToTokens;
use syn::parse::Parse;
use syn::Stmt;

mod derive_readable;
mod fastout;

/// Derives `Readable` for your own type.
///
/// If every member of your struct implements `Readable`, your own type can also be `Readable`.
/// All you have to do is just add `#[derive_readable]` to your type definition.  This macro
/// automatically implements `Readable` to your struct and translate your struct's member type to
/// the output type of the read.  For example, if you have `Usize1` in your struct, it will
/// actually be defined as `usize`.  Of course the `Usize1`'s  `Readable` implementation is used to
/// read.
#[proc_macro_attribute]
pub fn derive_readable(attr: TokenStream, input: TokenStream) -> TokenStream {
    derive_readable::main(attr, input)
}

/// Enables buffering for stdout.
///
/// You cannot create a closure containing `print!` or `println!` in `#[fastout]` function.  This
/// is because the closure cannot implement `Send` since `StdoutLock`, which is not a `Send`, is
/// internally captured into the closure.  This causes a trait bound mismatch when used with
/// function requiring its argument closure to be a `Send`, such as `std::thread::spawn()`.
///
/// ```compile_fail
/// use proconio::fastout;
///
/// use std::thread;
///
/// #[fastout]
/// fn main() {
///    thread::Builder::new()
///        .stack_size(32 * 1024 * 1024)
///        .spawn(|| {
///            println!("Hi!");
///        })
///        .unwrap()
///        .join()
///        .unwrap();
/// }
/// ```
///
/// It is too conservative to make all of such closures compilation error because it is actually no
/// problem to use such a closure only inside a single thread.  However, since trait bound check is
/// done after macro expansions, there is no way to check whther the closure is required to be a
/// `Send` or not.  And the compiler error message for actual mismatch of a `Send` requirement is
/// too confusing, pointing out codes you didn't write (macro-expanded codes) as an error position.
/// In conclusion, for user-friendliness, all of them are prohibited for now.
///
/// Internally this is the same with
///
/// ```
/// let __proconio_stdout = ::std::io::stdout();
/// let mut __proconio_stdout = ::std::io::BufWriter::new(__proconio_stdout.lock());
///
/// #[allow(unused_macros)]
/// macro_rules! print {
///     ($($tt:tt)*) => {{
///         use std::io::Write as _;
///         ::std::write!(__proconio_stdout, $($tt)*).unwrap();
///     }};
/// }
///
/// #[allow(unused_macros)]
/// macro_rules! println {
///     ($($tt:tt)*) => {{
///         use std::io::Write as _;
///         ::std::writeln!(__proconio_stdout, $($tt)*).unwrap();
///     }};
/// }
///
/// let __proconio_res = {
///     // Your code goes here
/// };
/// <::std::io::BufWriter<::std::io::StdoutLock> as ::std::io::Write>::flush(
///     &mut __proconio_stdout
/// ).unwrap();
/// return __proconio_res;
/// ```
#[proc_macro_attribute]
pub fn fastout(attr: TokenStream, input: TokenStream) -> TokenStream {
    fastout::main(attr, input)
}

fn compile_error_at(args: TokenStream2, start: Span2, end: Span2) -> Stmt {
    let start = start.unwrap();
    let end = end.unwrap();

    let group = TokenStream::from(args)
        .into_iter()
        .map(|x| set_span(x, Span::call_site()))
        .collect();

    let mut r = Vec::<TokenTree>::new();
    r.push(set_span(Ident::new("compile_error", start), start));
    r.push(set_span(Punct::new('!', Spacing::Alone), start));
    r.push(set_span(Group::new(Delimiter::Parenthesis, group), end));
    r.push(set_span(Punct::new(';', Spacing::Alone), end));

    syn::parse(r.into_iter().collect()).expect(concat!(
        "Failed to parse auto-generated compile_error! macro.  ",
        "This is a bug in `proconio`.  ",
        "Please report this issue from ",
        "<https://github.com/statiolake/proconio-rs/issues>."
    ))
}

fn set_span<T: Into<TokenTree>>(token: T, span: Span) -> TokenTree {
    let mut token = token.into();
    token.set_span(span);
    token
}

fn get_span_range(tokens: TokenStream) -> (Span, Span) {
    let mut tokens = tokens.into_iter();

    let start = match tokens.next() {
        Some(start) => start.span(),
        None => return (Span::call_site(), Span::call_site()),
    };
    let end = tokens.fold(start, |_, item| item.span());

    (start, end)
}

fn set_span_range<T: ToTokens + Parse>(tokens: T, start: Span, end: Span) -> T {
    let tokens = TokenStream::from(tokens.into_token_stream()).into_iter();

    let mut first = true;
    let tokens = tokens.map(|mut token| {
        if first {
            token.set_span(start);
            first = false;
        } else {
            token.set_span(end);
        }

        token
    });

    syn::parse(tokens.collect()).expect(concat!(
        "Failed to parse respanned token stream.  ",
        "This is a bug in `proconio`.  ",
        "Please report this issue from ",
        "<https://github.com/statiolake/proconio-rs/issues>."
    ))
}