Merge pull request #21548 from Shourya742/2026-01-29-decouple-codec-with-proc-macro

Make json and postcard protocols explicit, drop generic Codec

Author: Veykril

Cargo.lock

@@ -9,7 +9,7 @@ use paths::AbsPath;
 use span::Span;
 
 use crate::{
-    Codec, ProcMacro, ProcMacroKind, ServerError,
+    ProcMacro, ProcMacroKind, ServerError,
     bidirectional_protocol::msg::{
         BidirectionalMessage, ExpandMacro, ExpandMacroData, ExpnGlobals, Request, Response,
         SubRequest, SubResponse,
@@ -22,33 +22,33 @@ use crate::{
         },
     },
     process::ProcMacroServerProcess,
-    transport::codec::postcard::PostcardProtocol,
+    transport::postcard,
 };
 
 pub mod msg;
 
 pub type SubCallback<'a> = &'a dyn Fn(SubRequest) -> Result<SubResponse, ServerError>;
 
-pub fn run_conversation<C: Codec>(
+pub fn run_conversation(
     writer: &mut dyn Write,
     reader: &mut dyn BufRead,
-    buf: &mut C::Buf,
+    buf: &mut Vec<u8>,
     msg: BidirectionalMessage,
     callback: SubCallback<'_>,
 ) -> Result<BidirectionalMessage, ServerError> {
-    let encoded = C::encode(&msg).map_err(wrap_encode)?;
-    C::write(writer, &encoded).map_err(wrap_io("failed to write initial request"))?;
+    let encoded = postcard::encode(&msg).map_err(wrap_encode)?;
+    postcard::write(writer, &encoded).map_err(wrap_io("failed to write initial request"))?;
 
     loop {
-        let maybe_buf = C::read(reader, buf).map_err(wrap_io("failed to read message"))?;
+        let maybe_buf = postcard::read(reader, buf).map_err(wrap_io("failed to read message"))?;
         let Some(b) = maybe_buf else {
             return Err(ServerError {
                 message: "proc-macro server closed the stream".into(),
                 io: Some(Arc::new(io::Error::new(io::ErrorKind::UnexpectedEof, "closed"))),
             });
         };
 
-        let msg: BidirectionalMessage = C::decode(b).map_err(wrap_decode)?;
+        let msg: BidirectionalMessage = postcard::decode(b).map_err(wrap_decode)?;
 
         match msg {
             BidirectionalMessage::Response(response) => {
@@ -57,8 +57,9 @@ pub fn run_conversation<C: Codec>(
             BidirectionalMessage::SubRequest(sr) => {
                 let resp = callback(sr)?;
                 let reply = BidirectionalMessage::SubResponse(resp);
-                let encoded = C::encode(&reply).map_err(wrap_encode)?;
-                C::write(writer, &encoded).map_err(wrap_io("failed to write sub-response"))?;
+                let encoded = postcard::encode(&reply).map_err(wrap_encode)?;
+                postcard::write(writer, &encoded)
+                    .map_err(wrap_io("failed to write sub-response"))?;
             }
             _ => {
                 return Err(ServerError {
@@ -207,7 +208,7 @@ fn run_request(
     if let Some(err) = srv.exited() {
         return Err(err.clone());
     }
-    srv.run_bidirectional::<PostcardProtocol>(msg, callback)
+    srv.run_bidirectional(msg, callback)
 }
 
 pub fn reject_subrequests(req: SubRequest) -> Result<SubResponse, ServerError> {

crates/proc-macro-api/src/bidirectional_protocol.rs

@@ -1,13 +1,17 @@
 //! Bidirectional protocol messages
 
-use std::ops::Range;
+use std::{
+    io::{self, BufRead, Write},
+    ops::Range,
+};
 
 use paths::Utf8PathBuf;
 use serde::{Deserialize, Serialize};
 
 use crate::{
     ProcMacroKind,
     legacy_protocol::msg::{FlatTree, Message, PanicMessage, ServerConfig},
+    transport::postcard,
 };
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -97,4 +101,17 @@ pub struct ExpnGlobals {
     pub mixed_site: usize,
 }
 
-impl Message for BidirectionalMessage {}
+impl Message for BidirectionalMessage {
+    type Buf = Vec<u8>;
+
+    fn read(inp: &mut dyn BufRead, buf: &mut Self::Buf) -> io::Result<Option<Self>> {
+        Ok(match postcard::read(inp, buf)? {
+            None => None,
+            Some(buf) => Some(postcard::decode(buf)?),
+        })
+    }
+    fn write(self, out: &mut dyn Write) -> io::Result<()> {
+        let value = postcard::encode(&self)?;
+        postcard::write(out, &value)
+    }
+}

crates/proc-macro-api/src/bidirectional_protocol/msg.rs

@@ -18,8 +18,6 @@ use crate::{
         flat::serialize_span_data_index_map,
     },
     process::ProcMacroServerProcess,
-    transport::codec::Codec,
-    transport::codec::json::JsonProtocol,
     version,
 };
 
@@ -149,21 +147,21 @@ fn send_task(srv: &ProcMacroServerProcess, req: Request) -> Result<Response, Ser
         return Err(server_error.clone());
     }
 
-    srv.send_task::<_, _, JsonProtocol>(send_request::<JsonProtocol>, req)
+    srv.send_task_legacy::<_, _>(send_request, req)
 }
 
 /// Sends a request to the server and reads the response.
-fn send_request<P: Codec>(
+fn send_request(
     mut writer: &mut dyn Write,
     mut reader: &mut dyn BufRead,
     req: Request,
-    buf: &mut P::Buf,
+    buf: &mut String,
 ) -> Result<Option<Response>, ServerError> {
-    req.write::<P>(&mut writer).map_err(|err| ServerError {
+    req.write(&mut writer).map_err(|err| ServerError {
         message: "failed to write request".into(),
         io: Some(Arc::new(err)),
     })?;
-    let res = Response::read::<P>(&mut reader, buf).map_err(|err| ServerError {
+    let res = Response::read(&mut reader, buf).map_err(|err| ServerError {
         message: "failed to read response".into(),
         io: Some(Arc::new(err)),
     })?;

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

@@ -8,7 +8,7 @@ use paths::Utf8PathBuf;
 use serde::de::DeserializeOwned;
 use serde_derive::{Deserialize, Serialize};
 
-use crate::{Codec, ProcMacroKind};
+use crate::{ProcMacroKind, transport::json};
 
 /// Represents requests sent from the client to the proc-macro-srv.
 #[derive(Debug, Serialize, Deserialize)]
@@ -155,20 +155,40 @@ impl ExpnGlobals {
 }
 
 pub trait Message: serde::Serialize + DeserializeOwned {
-    fn read<C: Codec>(inp: &mut dyn BufRead, buf: &mut C::Buf) -> io::Result<Option<Self>> {
-        Ok(match C::read(inp, buf)? {
+    type Buf;
+    fn read(inp: &mut dyn BufRead, buf: &mut Self::Buf) -> io::Result<Option<Self>>;
+    fn write(self, out: &mut dyn Write) -> io::Result<()>;
+}
+
+impl Message for Request {
+    type Buf = String;
+
+    fn read(inp: &mut dyn BufRead, buf: &mut Self::Buf) -> io::Result<Option<Self>> {
+        Ok(match json::read(inp, buf)? {
             None => None,
-            Some(buf) => Some(C::decode(buf)?),
+            Some(buf) => Some(json::decode(buf)?),
         })
     }
-    fn write<C: Codec>(self, out: &mut dyn Write) -> io::Result<()> {
-        let value = C::encode(&self)?;
-        C::write(out, &value)
+    fn write(self, out: &mut dyn Write) -> io::Result<()> {
+        let value = json::encode(&self)?;
+        json::write(out, &value)
     }
 }
 
-impl Message for Request {}
-impl Message for Response {}
+impl Message for Response {
+    type Buf = String;
+
+    fn read(inp: &mut dyn BufRead, buf: &mut Self::Buf) -> io::Result<Option<Self>> {
+        Ok(match json::read(inp, buf)? {
+            None => None,
+            Some(buf) => Some(json::decode(buf)?),
+        })
+    }
+    fn write(self, out: &mut dyn Write) -> io::Result<()> {
+        let value = json::encode(&self)?;
+        json::write(out, &value)
+    }
+}
 
 #[cfg(test)]
 mod tests {

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

@@ -27,7 +27,6 @@ use semver::Version;
 use span::{ErasedFileAstId, FIXUP_ERASED_FILE_AST_ID_MARKER, Span};
 use std::{fmt, io, sync::Arc, time::SystemTime};
 
-pub use crate::transport::codec::Codec;
 use crate::{
     bidirectional_protocol::SubCallback, pool::ProcMacroServerPool, process::ProcMacroServerProcess,
 };

crates/proc-macro-api/src/lib.rs

@@ -17,7 +17,7 @@ use span::Span;
 use stdx::JodChild;
 
 use crate::{
-    Codec, ProcMacro, ProcMacroKind, ProtocolFormat, ServerError,
+    ProcMacro, ProcMacroKind, ProtocolFormat, ServerError,
     bidirectional_protocol::{self, SubCallback, msg::BidirectionalMessage, reject_subrequests},
     legacy_protocol::{self, SpanMode},
     version,
@@ -305,17 +305,17 @@ impl ProcMacroServerProcess {
         result
     }
 
-    pub(crate) fn send_task<Request, Response, C: Codec>(
+    pub(crate) fn send_task_legacy<Request, Response>(
         &self,
         send: impl FnOnce(
             &mut dyn Write,
             &mut dyn BufRead,
             Request,
-            &mut C::Buf,
+            &mut String,
         ) -> Result<Option<Response>, ServerError>,
         req: Request,
     ) -> Result<Response, ServerError> {
-        self.with_locked_io::<C, _>(|writer, reader, buf| {
+        self.with_locked_io(String::new(), |writer, reader, buf| {
             send(writer, reader, req, buf).and_then(|res| {
                 res.ok_or_else(|| {
                     let message = "proc-macro server did not respond with data".to_owned();
@@ -331,13 +331,12 @@ impl ProcMacroServerProcess {
         })
     }
 
-    pub(crate) fn with_locked_io<C: Codec, R>(
+    fn with_locked_io<R, B>(
         &self,
-        f: impl FnOnce(&mut dyn Write, &mut dyn BufRead, &mut C::Buf) -> Result<R, ServerError>,
+        mut buf: B,
+        f: impl FnOnce(&mut dyn Write, &mut dyn BufRead, &mut B) -> Result<R, ServerError>,
     ) -> Result<R, ServerError> {
         let state = &mut *self.state.lock().unwrap();
-        let mut buf = C::Buf::default();
-
         f(&mut state.stdin, &mut state.stdout, &mut buf).map_err(|e| {
             if e.io.as_ref().map(|it| it.kind()) == Some(io::ErrorKind::BrokenPipe) {
                 match state.process.exit_err() {
@@ -352,13 +351,13 @@ impl ProcMacroServerProcess {
         })
     }
 
-    pub(crate) fn run_bidirectional<C: Codec>(
+    pub(crate) fn run_bidirectional(
         &self,
         initial: BidirectionalMessage,
         callback: SubCallback<'_>,
     ) -> Result<BidirectionalMessage, ServerError> {
-        self.with_locked_io::<C, _>(|writer, reader, buf| {
-            bidirectional_protocol::run_conversation::<C>(writer, reader, buf, initial, callback)
+        self.with_locked_io(Vec::new(), |writer, reader, buf| {
+            bidirectional_protocol::run_conversation(writer, reader, buf, initial, callback)
         })
     }
 

crates/proc-macro-api/src/process.rs

@@ -1,3 +1,3 @@
 //! Contains construct for transport of messages.
-pub mod codec;
-pub mod framing;
+pub(crate) mod json;
+pub(crate) mod postcard;