Make pdb asyncio aware

Feature or enhancement

Proposal:

Currently pdb does not know anything about asyncio, even though it's a feature officially supported for a long time. I will add supports for asyncio in roughly 3 steps (does not have to be exact 3 PRs):

1. pdb will generate some passive info for asyncio. If the user hits a breakpoint inside an asyncio task, there will be a one line message with the current stack indicating which task the user is in. A convenience variable $_asynctask will be added to refer to the current task.
2. pdb will provide a way for the user to examine all the tasks in the current event loop with a new command. The user can inspect how many tasks are there and their status. Maybe they can even check the frames for each task.
3. pdb will enable users to switch between tasks, aka letting users to specify "run until I'm in this task". pdb will also possibly provide a way for the users to cancel the task.

In theory, many of the features are already possible with manual code as pdb can execute arbitrary code anyway. However, I believe it's helpful for the users to have a more convenient way to debug their async programs.

This was briefly mentioned in the language summit at PyCon this year, no one objected (maybe because they have other stuff that they were more against :) ).

This should not impact any user experience with the existing code that not involves asyncio.

If you have any other suggestions or objections, please let me know.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-124367
• gh-131258
• gh-131388
• gh-132576

Start by reviewing the existing pdb entry points and asyncio task and event-loop APIs. Compare the three proposed areas—task context, task inspection, and task switching or cancellation—and identify a narrowly scoped first change with tests. Done should include agreed behavior that preserves existing non-asyncio pdb use.