Variable inspection in the debugger sidebar

[JohanMabille]

Asking the variables with the sequence of StackTrace, Scopes and Variables requests does not work if execution did not stop on a breakpoint.

A solution to this would be to add a command in the protocol, let's say inspectVariables, that would make the interpreter execute globals and return its result.

[martinRenou]

Do you know why it's not in the Debug Adapter Protocol already?

[jtpio]

Asking the variables with the sequence of StackTrace, Scopes and Variables requests does not work if execution did not stop on a breakpoint.

This can be tested by calling:

const stackTrace = await debugSession.sendRequest('stackTrace', {
  threadId
});
console.log(stackTrace)

just before:

https://github.com/jupyterlab/debugger/blob/c9a0988a567f856b77ffbacd71083e460d7dcd16/tests/src/session.spec.ts#L149

Output:

{
  body: {},
  command: 'stackTrace',
  message: 'Wrong ID sent from the client: 1',
  request_seq: 5,
  seq: 7,
  success: false,
  type: 'response'
}

[JohanMabille]

The inspectVariables has been implemented in the back end. However globals returns a simple dictionary variable name - variable value while the variables panel expects an array of IVariables. We should either improve the backend so it returns an array of variables, or change the front end to transform the list of variables into a simple dictionary.

Last option would be to be able to pass different objects to the react component, but the view when stopped on a breakpoint and that when the execution has finished whould be inconsistent.

[jtpio]

Moving to the Future milestone.

[jtpio]

Also this inspectVariables request is meant to be used when the execution is not stopped. Typically the debugger could be enabled for a notebook, but the user would execute code as normal without breakpoints.

This also means that if a user wants to inspect children of a top-level variable (for example a nested dict or a class), the frontend could still send an execute_request to evaluate the variable directly, since there won't be any variableReference to send to the debugger.

[jtpio]

The latest version of xeus-python now follows the DAP for the inspectVariables response.

For more info:

• Follow the DAP for the inspectVariables response jupyter-xeus/xeus-python#194
• Follow the DAP for inspectVariables response jupyter-xeus/xeus-python#195

[jtpio]

xref #7873 which discusses inspecting Python objects.

[krassowski]

Closing as implemented in #10025 and released in 3.1. Please correct me if I am wrong here.

[JohanMabille]

Please notice the backend has been improved to return an array of IVariable when receiving an inspectVariable request. This way the behavior is consistent with the variables request and no further change is required in the frontend.

See ipython/ipykernel#753