feat: fallback to a synchronous main loop on WASM platforms

This should be all we need to add basic support for both pyodide and
wasi WASM runtimes

pygls/__init__.py

@@ -21,5 +21,7 @@
 
 IS_WIN = os.name == "nt"
 IS_PYODIDE = "pyodide" in sys.modules
+IS_WASI = sys.platform == "wasi"
+IS_WASM = IS_PYODIDE or IS_WASI
 
 pygls = "pygls"

pygls/server.py

@@ -25,8 +25,9 @@
 
 import cattrs
 
+from pygls import IS_WASM
 from pygls.exceptions import JsonRpcException, PyglsError
-from pygls.io_ import StdinAsyncReader, StdoutWriter, run_async, run_websocket
+from pygls.io_ import StdinAsyncReader, StdoutWriter, run, run_async, run_websocket
 from pygls.protocol import JsonRPCProtocol
 
 if typing.TYPE_CHECKING:
@@ -105,8 +106,18 @@ def report_server_error(self, error: Exception, source: ServerErrors):
     def start_io(
         self, stdin: Optional[BinaryIO] = None, stdout: Optional[BinaryIO] = None
     ):
-        """Starts IO server."""
-        logger.info("Starting IO server")
+        """Starts an IO server."""
+
+        if IS_WASM:
+            self._start_io_sync(stdin, stdout)
+        else:
+            self._start_io_async(stdin, stdout)
+
+    def _start_io_async(
+        self, stdin: Optional[BinaryIO] = None, stdout: Optional[BinaryIO] = None
+    ):
+        """Starts an asynchronous IO server."""
+        logger.info("Starting async IO server")
 
         self._stop_event = Event()
         reader = StdinAsyncReader(stdin or sys.stdin.buffer, self.thread_pool)
@@ -130,6 +141,33 @@ def start_io(
         finally:
             self.shutdown()
 
+    def _start_io_sync(
+        self, stdin: Optional[BinaryIO] = None, stdout: Optional[BinaryIO] = None
+    ):
+        """Starts an synchronous IO server."""
+        logger.info("Starting sync IO server")
+
+        self._stop_event = Event()
+        writer = StdoutWriter(stdout or sys.stdout.buffer)
+        self.protocol.set_writer(writer)
+
+        try:
+            asyncio.run(
+                run(
+                    stop_event=self._stop_event,
+                    reader=stdin or sys.stdin.buffer,
+                    protocol=self.protocol,
+                    logger=logger,
+                    error_handler=self.report_server_error,
+                )
+            )
+        except BrokenPipeError:
+            logger.error("Connection to the client is lost! Shutting down the server.")
+        except (KeyboardInterrupt, SystemExit):
+            pass
+        finally:
+            self.shutdown()
+
     def start_tcp(self, host: str, port: int) -> None:
         """Starts TCP server."""
         logger.info("Starting TCP server on %s:%s", host, port)