From: Derrick Stolee <stolee@gmail.com>

During the latest v2.45.0 update, 'scalar reconfigure --all' started to
segfault on my machine. Breaking it down via the debugger, it was
faulting on a NULL reference to the_hash_algo, which is a macro pointing
to the_repository->hash_algo.

In my case, this is due to one of my repositories having a detached HEAD,
which requires get_oid_hex() to parse that the HEAD reference is valid.
Another way to cause a failure is to use the "includeIf.onbranch" config
key, which will lead to a BUG() statement.

My first inclination was to try to refactor cmd_reconfigure() to execute
'git for-each-repo' instead of this loop. In addition to the difficulty
of executing 'scalar reconfigure' within 'git for-each-repo', it would
be difficult to perform the clean-up logic for non-existent repos if we
relied on that child process.

Instead, I chose to move the temporary repo to be within the loop and
reinstate the_repository to its old value after we are done performing
logic on the current array item.

Add tests to t9210-scalar.sh to test 'scalar reconfigure --all' with
multiple registered repos. There are two different ways that the old
use of the_repository could trigger bugs. These issues are being solved
independently to be more careful about the_repository being
uninitialized, but the change in this patch around the use of
the_repository is still a good safety precaution.

Co-authored-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Derrick Stolee <stolee@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.1724.v3.git.1715126749391.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1724.git.1714496333004.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1724.v2.git.1714874298859.gitgitgadget@gmail.com