gh-118714: Make the pdb post-mortem restart/quit behavior more reasonable

[gaogaotiantian]

Currently the restart and quit behavior of pdb post-mortem debugging mode is a bit weird.

As the issue mentioned, if the user uses quit or hit Ctrl+D in post-mortem debugging mode, the debugger will quit, but with a message of the script will be restarted. If the user uses restart command, an exception will be raised and the debugger will quit due to the exception.

This PR is to clean up the bahaviors. In post-mortem debugging, the user can:

• use restart to restart
• use cont / step to restart as instructed
• use quit or Ctrl+D to quit

The message will always informing the users that they are restarting the program if they try to restart, and will quietly quit when they quit.

I would consider this a bug fix so it should not be affected by beta freeze to be merged into 3.13.

• Issue: Change in pdb behavior at exit from post-mortem debugger #118714

[gaogaotiantian]

Hi @iritkatriel , as this is a bug fix, I'd like to make it simple and correct. As I said, printing stuff in do_restart will raise the issue of incorrectly using restart command when the user should not (pdb brought up by breakpoint() and there's no way to restart). I plan to clean up the structure to disallow users to use certain commands (run/restart) when they are not supposed to and generate some warnings in some cases (Ctrl+D in inline pdb will just stop the process). All above require some feature work (customize pdb.Pdb with some arguments like allow_restart, which is only set when pdb is brought up by command line interface) and should not be backported.

So could we maybe do the quick fix first and backport, then I'll make it better in 3.14.

[iritkatriel]

This isn't very clear. Also, it seems inconsistent with the title of this PR. Are you changing the behaviour (as the title says) or changing the message to match the behaviour?

[gaogaotiantian]

Both behavior and message were changed. There were two cases involved, both under post-mortem debugging:

1. If the user does restart, it actually restarts the program, instead of raising an error and exit. (This is the behavior change).
2. If the user does quit, it quits the program without printing the line saying "we'll restart the program".

I think I should make the behavior change clearer (it's considered a bug fix because quitting the debugger when doing restart feels wrong).

[gaogaotiantian]

I forgot to change this after the review. Just changed it. Let me know if you think this could be better.

[iritkatriel]

If you want to backport you need the backport labels. We use the green ones on issues.

[gaogaotiantian]

Yeah I don't know why I added the issue tags back then. I'll only backport this to 3.13, as that's the version with the behavior change. I'll leave 3.12 alone.

[miss-islington-app]

Thanks @gaogaotiantian for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-121346 is a backport of this pull request to the 3.13 branch.