[3.12] Lambda generators cause assertion failure: `python: Objects/genobject.c:400: gen_close: Assertion `exception_handler_depth > 0' failed.`

[mgorny]

Crash report

What happened?

When CPython 3.12 is built with assertions enabled, the following snippet causes the interpreter to crash:

x = lambda: (yield 3)
next(x())

$ ./python /tmp/LambdasTest.py 
python: Objects/genobject.c:400: gen_close: Assertion `exception_handler_depth > 0' failed.
Aborted (core dumped)

This doesn't happen with 3.11 or with main. From a quick bisect:

• [3.12] gh-100762: Fix optimization in gen_close (GH-111069) #115818 (eb4774d) broke it on 3.12
• gh-111354: simplify detection of RESUME after YIELD_VALUE at except-depth 1  #111459 (52cc4af) fixed it on main

This was triggered in the wild by Nuitka's test suite: Nuitka/Nuitka#2893.

CC @iritkatriel

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.12.3+ (heads/3.12:6d9677d78e, Jun 1 2024, 11:06:51) [GCC 14.1.1 20240516]

Linked PRs

• [3.12] gh-119897: Revert buggy optimization which was removed in 3.13 #120467
• gh-119897: Add test for lambda generator invocation #120658
• [3.13] gh-119897: Add test for lambda generator invocation (GH-120658) #120673

[mgorny]

Gentle ping.

[mgorny]

Given no reply, I'm going to revert this change in Gentoo. Hope that doesn't cause more issues.

[iritkatriel]

Thanks. I agree, let's revert the bad commit in 3.12.

[iritkatriel]

Thanks.