Catch a syntax error when parsing an input file with the --stay-connected flag active

CHANGELOG.md

@@ -6,6 +6,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed 
+- The `run` command now catches syntax errors in the input file. ([pybricksdev#126]) 
+
+[pybricksdev#126]: https://github.com/pybricks/pybricksdev/pull/126
+
 ## [2.3.0] - 2025-10-31
 
 ### Added

pybricksdev/cli/__init__.py

@@ -25,6 +25,7 @@
 from pybricksdev.connections.pybricks import (
     HubDisconnectError,
     HubPowerButtonPressedError,
+    PybricksHub,
 )
 
 PROG_NAME = (
@@ -184,70 +185,7 @@ def add_parser(self, subparsers: argparse._SubParsersAction):
 
     async def run(self, args: argparse.Namespace):
 
-        # Pick the right connection
-        if args.conntype == "ble":
-            from pybricksdev.ble import find_device as find_ble
-            from pybricksdev.connections.pybricks import PybricksHubBLE
-
-            # It is a Pybricks Hub with BLE. Device name or address is given.
-            print(f"Searching for {args.name or 'any hub with Pybricks service'}...")
-            device_or_address = await find_ble(args.name)
-            hub = PybricksHubBLE(device_or_address)
-        elif args.conntype == "usb":
-            from usb.core import find as find_usb
-
-            from pybricksdev.connections.pybricks import PybricksHubUSB
-            from pybricksdev.usb import (
-                EV3_USB_PID,
-                LEGO_USB_VID,
-                MINDSTORMS_INVENTOR_USB_PID,
-                NXT_USB_PID,
-                SPIKE_ESSENTIAL_USB_PID,
-                SPIKE_PRIME_USB_PID,
-            )
-
-            def is_pybricks_usb(dev):
-                return (
-                    (dev.idVendor == LEGO_USB_VID)
-                    and (
-                        dev.idProduct
-                        in [
-                            NXT_USB_PID,
-                            EV3_USB_PID,
-                            SPIKE_PRIME_USB_PID,
-                            SPIKE_ESSENTIAL_USB_PID,
-                            MINDSTORMS_INVENTOR_USB_PID,
-                        ]
-                    )
-                    and dev.product.endswith("Pybricks")
-                )
-
-            device_or_address = find_usb(custom_match=is_pybricks_usb)
-
-            if device_or_address is None:
-                print("Pybricks Hub not found.", file=sys.stderr)
-                exit(1)
-
-            hub = PybricksHubUSB(device_or_address)
-        else:
-            raise ValueError(f"Unknown connection type: {args.conntype}")
-
-        # Connect to the address and run the script
-        await hub.connect()
-        try:
-            with _get_script_path(args.file) as script_path:
-                if args.start:
-                    await hub.run(script_path, args.wait or args.stay_connected)
-                else:
-                    if args.stay_connected:
-                        # if the user later starts the program by pressing the button on the hub,
-                        # we still want the hub stdout to print to Python's stdout
-                        hub.print_output = True
-                        hub._enable_line_handler = True
-                    await hub.download(script_path)
-
-            if not args.stay_connected:
-                return
+        async def stay_connected_menu(hub: PybricksHub):
 
             class ResponseOptions(IntEnum):
                 RECOMPILE_RUN = 0
@@ -359,6 +297,10 @@ async def reconnect_hub():
                         case _:
                             return
 
+                except SyntaxError as e:
+                    print("\nA syntax error occurred while parsing your program:")
+                    print(e, "\n")
+
                 except HubPowerButtonPressedError:
                     # This means the user pressed the button on the hub to re-start the
                     # current program, so the menu was canceled and we are now printing
@@ -375,6 +317,77 @@ async def reconnect_hub():
                     await asyncio.sleep(0.3)
                     hub = await reconnect_hub()
 
+        # Pick the right connection
+        if args.conntype == "ble":
+            from pybricksdev.ble import find_device as find_ble
+            from pybricksdev.connections.pybricks import PybricksHubBLE
+
+            # It is a Pybricks Hub with BLE. Device name or address is given.
+            print(f"Searching for {args.name or 'any hub with Pybricks service'}...")
+            device_or_address = await find_ble(args.name)
+            hub = PybricksHubBLE(device_or_address)
+        elif args.conntype == "usb":
+            from usb.core import find as find_usb
+
+            from pybricksdev.connections.pybricks import PybricksHubUSB
+            from pybricksdev.usb import (
+                EV3_USB_PID,
+                LEGO_USB_VID,
+                MINDSTORMS_INVENTOR_USB_PID,
+                NXT_USB_PID,
+                SPIKE_ESSENTIAL_USB_PID,
+                SPIKE_PRIME_USB_PID,
+            )
+
+            def is_pybricks_usb(dev):
+                return (
+                    (dev.idVendor == LEGO_USB_VID)
+                    and (
+                        dev.idProduct
+                        in [
+                            NXT_USB_PID,
+                            EV3_USB_PID,
+                            SPIKE_PRIME_USB_PID,
+                            SPIKE_ESSENTIAL_USB_PID,
+                            MINDSTORMS_INVENTOR_USB_PID,
+                        ]
+                    )
+                    and dev.product.endswith("Pybricks")
+                )
+
+            device_or_address = find_usb(custom_match=is_pybricks_usb)
+
+            if device_or_address is None:
+                print("Pybricks Hub not found.", file=sys.stderr)
+                exit(1)
+
+            hub = PybricksHubUSB(device_or_address)
+        else:
+            raise ValueError(f"Unknown connection type: {args.conntype}")
+
+        # Connect to the address and run the script
+        await hub.connect()
+        try:
+            with _get_script_path(args.file) as script_path:
+                if args.start:
+                    await hub.run(script_path, args.wait or args.stay_connected)
+                else:
+                    if args.stay_connected:
+                        # if the user later starts the program by pressing the button on the hub,
+                        # we still want the hub stdout to print to Python's stdout
+                        hub.print_output = True
+                        hub._enable_line_handler = True
+                    await hub.download(script_path)
+
+            if args.stay_connected:
+                await stay_connected_menu(hub)
+
+        except SyntaxError as e:
+            print("\nA syntax error occurred while parsing your program:")
+            print(e, "\n")
+            if args.stay_connected:
+                await stay_connected_menu(hub)
+
         finally:
             await hub.disconnect()