Re: [PATCH 12/12] hash: stop depending on `the_repository` in `null_oid()`

> The `null_oid()` function returns the object ID that only consists of
> zeroes. Naturally, this ID also depends on the hash algorithm used, as
> the number of zeroes is different between SHA1 and SHA256. Consequently,
> the function returns the hash-algorithm-specific null object ID.
> 
> This is currently done by depending on `the_hash_algo`, which implicitly
> makes us depend on `the_repository`. Refactor the function to instead
> pass in the hash algorithm for which we want to retrieve the null object
> ID. Adapt callsites accordingly by passing in `the_repository`, thus
> bubbling up the dependency on that global variable by one layer.
> 
> There are a couple of trivial exceptions for subsystems that already got
> rid of `the_repository`. These subsystems instead use the repository
> that is available via the calling context:
> 
>   - "builtin/grep.c"
>   - "grep.c"
>   - "refs/debug.c"
> 
> There is also a single non-trivial exception with "diff-no-index.c".
> Here we know that we may not have a repository initialized at all, so we
> cannot rely on `the_repository`. Instead, we adapt `diff_no_index()` to
> get a `struct git_hash_algo` as parameter. The only caller is located in
> "builtin/diff.c", where we know to call `repo_set_hash_algo()` in case
> we're running outside of a Git repository. Consequently, it is fine to
> continue passing `the_repository->hash_algo` even in this case.
> 
> This means that we could in theory just not bother about this edge case
> at all and just use `the_repository` in "diff-no-index.c". But doing so
> would feel misdesigned.
> 
> Remove the `USE_THE_REPOSITORY_VARIABLE` preprocessor define in
> "hash.c".
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---

> -int diff_no_index(struct rev_info *revs,
> -		  int implicit_no_index,
> -		  int argc, const char **argv)
> +int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
> +		  int implicit_no_index, int argc, const char **argv)

>  {
>  	int i, no_index;
>  	int ret = 1;
> @@ -354,7 +354,7 @@ int diff_no_index(struct rev_info *revs,
>  	setup_diff_pager(&revs->diffopt);
>  	revs->diffopt.flags.exit_with_status = 1;
>  
> -	if (queue_diff(&revs->diffopt, paths[0], paths[1], 0))
> +	if (queue_diff(&revs->diffopt, algop, paths[0], paths[1], 0))
>  		goto out;
>  	diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/");
>  	diffcore_std(&revs->diffopt);