Ignore proc-macro stdout to prevent IPC crash

crates/proc_macro_api/src/msg.rs

@@ -77,13 +77,24 @@ impl Message for Request {}
 impl Message for Response {}
 
 fn read_json(inp: &mut impl BufRead) -> io::Result<Option<String>> {
+    loop {
         let mut buf = String::new();
         inp.read_line(&mut buf)?;
         buf.pop(); // Remove trailing '\n'
-    Ok(match buf.len() {
+
-        0 => None,
+        if buf.is_empty() {
-        _ => Some(buf),
+            return Ok(None);
-    })
+        }
+
+        // Some ill behaved macro try to use stdout for debugging
+        // We ignore it here
+        if !buf.starts_with("{") {
+            log::error!("proc-macro tried to print : {}", buf);
+            continue;
+        }
+
+        return Ok(Some(buf));
+    }
 }
 
 fn write_json(out: &mut impl Write, msg: &str) -> io::Result<()> {

crates/rust-analyzer/tests/rust-analyzer/main.rs

@@ -712,6 +712,10 @@ pub fn foo(_input: TokenStream) -> TokenStream {
     // We hard code the output here for preventing to use any deps
     let mut res = TokenStream::new();
 
+    // ill behaved proc-macro will use the stdout
+    // we should ignore it
+    println!("I am bad guy");
+
     // impl Bar for Foo { fn bar() {} }
     let mut tokens = vec![t!("impl"), t!("Bar"), t!("for"), t!("Foo")];
     let mut fn_stream = TokenStream::new();