gh-146355: Fix main_module ref leak in _PyRun_SimpleStringFlagsWithName

[A0su]

gh-146355: Fix main_module ref leak in _PyRun_SimpleStringFlagsWithName

This is a sub-issue for #146102 and original gist details can be found here

When the_name is NULL we'll fail to call Py_DECREF on main_module. I used the same goto pattern as _PyRun_SimpleFileObject to fix this.

I omitted a new test entry as we have indirect coverage of functionality in test_embed.py. Not sure if it makes sense for the scope of fixing the ref leak to include the additional code for a test in test_run.py (which has a TODO for this function).

[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.

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[vstinner]

I dislike this change. IMO it makes the code harder to follow and more complex. I would prefer just that to fix the leak:

diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index a21f494dc69..1e327848e65 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -567,6 +567,7 @@ _PyRun_SimpleStringFlagsWithName(const char *command, const char* name, PyCompil
         PyObject* the_name = PyUnicode_FromString(name);
         if (!the_name) {
             PyErr_Print();
+            Py_DECREF(main_module);
             return -1;
         }
         res = _PyRun_StringFlagsWithName(command, the_name, Py_file_input, dict, dict, flags, 0);

It's a single line to fix the leak.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[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.

[A0su]

I have made the requested changes; please review again.

[bedevere-app]

Thanks for making the requested changes!

@vstinner: please review the changes made to this pull request.