fetch-pack: match refs exactly

fetch-pack: match refs exactly

When we are determining the list of refs to fetch via
fetch-pack, we have two sets of refs to compare: those on
the remote side, and a "match" list of things we want to
fetch. We iterate through the remote refs alphabetically,
seeing if each one is wanted by the "match" list.

Since def88e9 (Commit first cut at "git-fetch-pack",
2005-07-04), we have used the "path_match" function to do a
suffix match, where a remote ref is considered wanted if
any of the "match" elements is a suffix of the remote
refname.

This enables callers of fetch-pack to specify unqualified
refs and have them matched up with remote refs (e.g., ask
for "A" and get remote's "refs/heads/A"). However, if you
provide a fully qualified ref, then there are corner cases
where we provide the wrong answer. For example, given a
remote with two refs:

   refs/foo/refs/heads/master
   refs/heads/master

asking for "refs/heads/master" will first match
"refs/foo/refs/heads/master" by the suffix rule, and we will
erroneously fetch it instead of refs/heads/master.

As it turns out, all callers of fetch_pack do provide
fully-qualified refs for the match list. There are two ways
fetch_pack can get match lists:

  1. Through the transport code (i.e., via git-fetch)

  2. On the command-line of git-fetch-pack

In the first case, we will always be providing the names of
fully-qualified refs from "struct ref" objects. We will have
pre-matched those ref objects already (since we have to
handle more advanced matching, like wildcard refspecs), and
are just providing a list of the refs whose objects we need.

In the second case, users could in theory be providing
non-qualified refs on the command-line. However, the
fetch-pack documentation claims that refs should be fully
qualified (and has always done so since it was written in
2005).

Let's change this path_match call to simply check for string
equality, matching what the callers of fetch_pack are
expecting.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>