Re: [PATCH 7/7] hash: check ctx->active flag in all wrapper functions

[Patrick Steinhardt <ps@pks.im>]

On Tue, Jul 07, 2026 at 01:09:52AM -0400, Jeff King wrote:
> It only makes sense to call git_hash_update(), etc, on a hash context
> that has been initialized but not yet finalized or discarded. This is an
> unlikely error to make, but it's easy for us to catch it and complain.
> 
> It's especially important because it would quietly "work" for many hash
> backends (like sha1dc, which is just manipulating some bytes) but would
> cause undefined behavior with others (like OpenSSL, which puts the
> context onto the heap). Checking the flag lets us catch problems
> consistently on every build.
> 
> Note that we can't do the same for git_init_hash(). Even though it would

You probably mean `git_hash_init()`?

> cause a leak to call it twice (without an intervening final/discard),
> the point of the function is that the contents of the struct are
> undefined before the call. But calling it twice is an even less likely
> error to make, so not covering it is OK.

Right. We could of course enforce that the structure must be zeroed
before calling this function. But I agree that this would become quite
awkward.

Patrick