New Feature: Single Step Debugger Support

[gerth2]

Problem description

Basic debug support through debugpy works well today with vsCode.

Documenting this here for potential future integration.

Overall design goal: single-click debugger activation that lets you walk code line by line on a development computer, while execution is happening on the RIO.

1. Standard vsCode python extensions
2. install debugpy on both the RIO and local desktop
3. Add a vsCode task to start the robot in debug mode - for us, this involves dropping a blank file with a magic name in the RIO's filesystem, then restarting the robot code
4. a small snippet of code in the robot main code to detect the "wait for debugger" file trigger and wait for a debug connection.

tasks.json:

        {
            "label": "PyFRC: _Activate Debug",
            "type": "shell",
            "windows": {
                "command": "ssh lvuser@roboRIO-1736-FRC.local -t 'chmod +x ./robotCommand; touch /home/lvuser/py/enableDebug; ./robotCommand || true; echo Waiting for robot program to start...; sleep 5' "
            },
            "linux": {
                "command": "ssh lvuser@roboRIO-1736-FRC.local -t 'chmod +x ./robotCommand; touch /home/lvuser/py/enableDebug; ./robotCommand || true; echo Waiting for robot program to start...; sleep 5' "
            },
            "group": {
                "kind": "build",
            },
            "presentation": {
                "reveal": "always",
                "panel": "dedicated",
                "clear": true,
                "focus": true,
                "showReuseMessage": false
            },
            "problemMatcher": [],
            "icon": {
                "id": "cloud-upload"
            }
        },

launch.json:

...
        {
            "name": "Debug RoboRIO",
            "type": "python",
            "request": "attach",
            "connect": {
                "host": "roboRIO-1736-frc.local",
                "port": 5678
            },
            "pathMappings": [
                {
                    "localRoot": "${workspaceFolder}",
                    "remoteRoot": "/home/lvuser/py"
                }
            ],
            "justMyCode": true,
            "preLaunchTask": "PyFRC: _Activate Debug"
        },
...

Robot Code:

if __name__ == '__main__':

    enableDebug = os.path.isfile("/home/lvuser/py/enableDebug")
    if(enableDebug):
        print("Starting Debug Support....")
        import debugpy 
        debugpy.listen(('0.0.0.0', 5678))
        debugpy.wait_for_client()

    wpilib.run(MyRobot)

The real trick is just to make sure the robot code gets restarted with the correct value for enableDebug - it does slow down execution noticeably, and isn't something I think you'd want all the time.

I've got no idea if there's a better way than a file (environment variables?), but that just seemed to be the most reliable way.

One nice thingabout using a file: if the code is simply redeployed, the file is wiped away, so the code goes back to "normal/non-debug" mode.

Hopefully helps? Other than the funkiness of the file itself, I'd highly recommend the rest.

Operating System

Windows

Installed Python Packages

N/A

Reproducible example code

N/A

[auscompgeek]

you can deploy in debug mode already, no need for a complex ssh command

./robot.py deploy --debug

this can be detected with __debug__ e.g.

if __name__ == "__main__":
    if __debug__:
        try:
            import debugpy
        except ModuleNotFoundError:
            pass
        else:
            debugpy.listen(('0.0.0.0', 5678))

    wpilib.run(MyRobot)

[gerth2]

that is way better than magic files. One moment please...

[gerth2]

https://github.com/RobotCasserole1736/firstRoboPy/blob/chris_daves_dandy_debug_design/.vscode/tasks.json

https://github.com/RobotCasserole1736/firstRoboPy/blob/chris_daves_dandy_debug_design/robot.py#L117

Updated, works well.

Tasks is a bit more complex now, to keep a "single button" paradigm I had to chain together the deploy with --debug and a short pause to let the RIO get up and running before the host PC tries to connect (otherwise vscode was giving me a connection refused error)

Also, in the code stnippet, I added inspection to check that we were indeed running the code, not deploying or simulating. Otherwise, it's likely that debug is true, which will stall things out.

I do think it's valid for teams to want to be able to walk through robotInit(), so I included the debugpy.wait_for_client() call to facilitate that.

[auscompgeek]

See also previous discussion: robotpy/robotpy-wpilib#99