[PATCH] upload-pack: fix broken if/else chain in config callback

The upload_pack_config() callback uses an if/else chain like:

  if (!strcmp(var, "a"))
     ...
  else if (!strcmp(var, "b"))
     ...
  etc

This works as long as the conditions are mutually exclusive, but one of them is not. 20b20a22f8 (upload-pack: provide a hook for running pack-objects, 2016-05-18) added:

  else if (current_config_scope() != CONFIG_SCOPE_REPO) {
     ... check some more options ...
  }

That was fine in that commit, because it came at the end of the chain. But later, 10ac85c785 (upload-pack: add object filtering for partial clone, 2017-12-08) did this:

  else if (current_config_scope() != CONFIG_SCOPE_REPO) {
     ... check some more options ...
  } else if (!strcmp("uploadpack.allowfilter", var))
     ...

We'd always check the scope condition first, meaning we'd _only_ respect allowfilter when it's in the repo config. You can see this with:

  git -c uploadpack.allowfilter=true upload-pack . | head -1

which will not advertise the filter capability (but will after this patch). We never noticed because:

  - our tests always set it in the repo config

  - in protocol v2, we use a different code path that
    actually calls repo_config_get_bool() separately, so
    that _does_ work. Real-world people experimenting with
    this may be using v2.

The more recent uploadpack.allowrefinwant option is in the same boat.

There are a few possible fixes:

  1. Bump the scope conditional back to the bottom of the
     chain. But that just means somebody else is likely to
     make the same mistake later.

  2. Make the conditional more like the others. I.e.:

       else if (!current_config_scope() != CONFIG_SCOPE_REPO &&
                !strcmp(var, "uploadpack.notallowedinrepo"))

     This works, but the idea of the original structure was
     that we may grow multiple sensitive options like this.

  3. Pull it out of the chain entirely. The chain mostly
     serves to avoid extra strcmp() calls after we've found
     a match. But it's not worth caring about those. In the
     worst case, when there isn't a match, we're already
     hitting every strcmp (and this happens regularly for
     stuff like "core.bare", etc).

This patch does (3).

Signed-off-by: Jeff King <peff@peff.net>
---
Phew. That was a lot of explanation for a small patch, but
this was sufficiently subtle I thought it worth it. And
also, I was really surprised the bug managed to exist for
this long without anybody noticing.

 upload-pack.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)