gh-141982: Fix pdb can't set breakpoints on async functions

[cocolato]

Fix: #141982

I found that while debugging with pdb you currently cannot set a breakpoint on an async function. Reproducer:

import asyncio

async def main():
    print(f"Hello")
    await asyncio.sleep(1)
    print(f"World!")

asyncio.run(main())

If you run pdb and try to set a breakpoint on main you get:

λ › ./python -m pdb main.py                                                                                                                                          
> /cpython/main.py(1)<module>()
-> import asyncio
(Pdb) break main
*** The specified object 'main' is not a function or was not found along sys.path.
(Pdb) quit

This happens because the regular expression used by find_function does not match async functions:

cpython/Lib/pdb.py

Lines 132 to 133 in 2ff8608

	def find_function(funcname, filename):
	cre = re.compile(r'def\s+%s(\s*\[.+\])?\s*[(]' % re.escape(funcname))

After the fix:

λ › ./python -m pdb main.py                                                                                                                                          
> /cpython/main.py(1)<module>()
-> import asyncio
(Pdb) break main
Breakpoint 1 at /cpython/main.py:4
(Pdb) continue
> /cpython/main.py(4)main()
-> print(f"Hello")
(Pdb) quit

Now we can set breakpoints on async functions as expected.

• Issue: Support pdb breakpoints on async functions #141982

[bedevere-app]

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[aisk]

I'm not familiar with the pdb module, but I think that even after this change, functions defined within an if branch or other indented blocks still can't be found by this function. Perhaps we could use another approach, like walking the AST in the find_function to handle this situation.

For now, however, I think it's acceptable to just handle the async function case described in the original issue because this is the most common situation.

[gaogaotiantian]

Let's optimize the test case a bit. So we want a test case that is accurate and comprehensive, while being concise. The sleep and World part did not do anything - we don't need them.

Checking Hello is not the best practice because there could be many ways that Hello appears in stdout - it's part of the source code and you are printing it. Say the breakpoint is never set, you'd still have Hello in stdout.

One way is to check World is not printed out - which could be an indicator that a breakpoint is set. For Hello I think we need to check it in a better way.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[cocolato]

Thanks for review, @gaogaotiantian ! Do you think the current tests are sufficient?

[gaogaotiantian]

Thank you for fixing this.