Description:
I'm seeing segfaults when trying to perform a sysupgrade, but only if transaction.to_add and transaction.to_remove are accessed.

Package versions:
pyalpm 0.10.4-1
python 3.9.5-3
pacman 6.0.0-3

Steps to reproduce:

The behaviour is pretty weird, varying slightly depending on the order of operations.

To reproduce, I have an executable script that always starts with the following code:

---

#!/usr/bin/python3

import pycman.config
import pycman.transaction

handle = pycman.confi.init_with_config("/etc/pacman.conf")
transaction = pycman.transaction.init_from_options(handle, {})
transaction.sysupgrade(False)

---

From here, the behaviour varies depending on the order of the next few instructions. If the rest of the script looks like this:

print(transaction.to_add)
print(transaction.to_remove)
transaction.release()
print("released")

Then the script segfaults upon accessing transaction.to_remove.

If the rest of the script looks like this:

print(transaction.to_add)
transaction.release()
print("released")

Then the script segfaults upon calling transaction.release().

If the rest of the script looks like this:

print(transaction.to_remove)
print(transaction.to_add)
transaction.release()
print("released")

Then the script segfaults upon calling transaction.release().

If the rest of the script looks like this:

print(transaction.to_remove)
transaction.release()
print("released")

Then the script completes successfully without segfaulting.

If transaction.release() is called without ever accessing transaction.to_add, the script completes successfully.

To confirm:

- The same results occurred regardless of whether or not print statements were used. I used print statements simply to aid the initial diagnosis.
- Every time the script segfaulted, I had to manually clear the lock file /var/lib/pacman/db.lck before I was able to try it again.
- I tested elevating privileges using both sudo and doas, and it had the same effect.
- I observe what appears to be the exact same segfault when running 'pycman-sync -u' (with both sudo and doas).
- While performing these tests, I have three packages awaiting upgrades. I arbitrarily downgraded these packages in order to test:

broot 1.5.1-1 -> 1.6.0-1
typescript 4.3.2-1 -> 4.3.4-1
vlc 3.0.15-2 -> 3.0.16-1

Please let me know if I can provide any further information that would assist debugging.