[3.10] gh-91924: Fix __ltrace__ for non-UTF-8 stdout encoding

[vstinner]

Fix ltrace debug feature if the stdout encoding is not UTF-8.

If the stdout encoding is not UTF-8, the first call to
lltrace_resume_frame() indirectly sets lltrace to 0 when calling
unicode_check_encoding_errors() which calls
encodings.search_function().

Add test_lltrace.test_lltrace() test.

[vstinner]

@sweeneyde @serhiy-storchaka: Would you mind to review this fix for Python 3.10? The fix is different and I adapted the test from the main branch for 3.10.

Without the fix but with the new test, LC_ALL=en_US.iso88591 ./python -m test test_lltrace fails. With the fix, the test pass.

[sweeneyde]

I'm not sure why Windows CI is failing, the tests pass on my Windows machine.

Maybe it has something to do with not calling fflush(stdout) at the end of prtrace? Or maybe it's an encoding issue?

[vstinner]

I'm not sure why Windows CI is failing, the tests pass on my Windows machine.

In the 3.10 branch, the Windows CI builds Python in release mode. I fixed the test.

[vstinner]

@sweeneyde: the CI tests now pass.

[sweeneyde]

Looks good to me. The local variable is nicer, but I agree that minimizing changes (EXT_POP and call_function) is more important.

[vstinner]

The local variable is nicer, but I agree that minimizing changes (EXT_POP and call_function) is more important.

Adding an argument to call_function() can make the performance worse, and the code more complicated depending if LLTRACE macro is defined or not. I really want to minimize the risk of regression in 3.10 stable branch. __ltrace__ is a niche debug tool, it's mostly used by core developers to hack Python.

[vstinner]

I hesitated to fix __ltrace__ typo: add a second L, but Python 3.10.0 was released last year, I prefer to not change it in a minor 3.10.x release. It's also documented at: https://docs.python.org/3.10/using/configure.html#python-debug-build

[vstinner]

It reminds me the weird typo of float.__set_format__(): it was previously known as float.__setformat__() in Python 3.7. I removed the method in Python 3.11.

[vstinner]

Oh, for the float method, I backported my change fixing the typo: #31558