crates/proc-macro-api/src/legacy_protocol/json.rs

//! Protocol functions for json.
use std::io::{self, BufRead, Write};

use serde::{Serialize, de::DeserializeOwned};

use crate::{codec::Codec, framing::Framing};

pub struct JsonProtocol;

impl Framing for JsonProtocol {
    type Buf = String;

    fn read<'a, R: BufRead>(
        inp: &mut R,
        buf: &'a mut String,
    ) -> io::Result<Option<&'a mut String>> {
        loop {
            buf.clear();

            inp.read_line(buf)?;
            buf.pop(); // Remove trailing '\n'

            if buf.is_empty() {
                return Ok(None);
            }

            // Some ill behaved macro try to use stdout for debugging
            // We ignore it here
            if !buf.starts_with('{') {
                tracing::error!("proc-macro tried to print : {}", buf);
                continue;
            }

            return Ok(Some(buf));
        }
    }

    fn write<W: Write>(out: &mut W, buf: &String) -> io::Result<()> {
        tracing::debug!("> {}", buf);
        out.write_all(buf.as_bytes())?;
        out.write_all(b"\n")?;
        out.flush()
    }
}

impl Codec for JsonProtocol {
    fn encode<T: Serialize>(msg: &T) -> io::Result<String> {
        Ok(serde_json::to_string(msg)?)
    }

    fn decode<T: DeserializeOwned>(buf: &mut String) -> io::Result<T> {
        let mut deserializer = serde_json::Deserializer::from_str(buf);
        // Note that some proc-macro generate very deep syntax tree
        // We have to disable the current limit of serde here
        deserializer.disable_recursion_limit();
        Ok(T::deserialize(&mut deserializer)?)
    }
}