Re: [PATCH v3] scalar: avoid segfault in reconfigure --all

> 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>