checkout.c: use ref_exists instead of file_exist

Change checkout.c to check if a ref exists instead of checking if a loose ref
file exists when deciding if to delete an orphaned log file. Otherwise, if a
ref only exists as a packed ref without a corresponding loose ref for the
currently checked out branch, we risk that the reflog will be deleted when we
switch to a different branch.

Update the reflog tests to check for this bug.

The following reproduces the bug:
$ git init-db
$ git config core.logallrefupdates true
$ git commit -m Initial --allow-empty
    [master (root-commit) bb11abe] Initial
$ git reflog master
    [8561dcb master@{0}: commit (initial): Initial]
$ find .git/{refs,logs} -type f | grep master
    [.git/refs/heads/master]
    [.git/logs/refs/heads/master]
$ git branch foo
$ git pack-refs --all
$ find .git/{refs,logs} -type f | grep master
    [.git/logs/refs/heads/master]
$ git checkout foo
$ find .git/{refs,logs} -type f | grep master
    ... reflog file is missing ...
$ git reflog master
    ... nothing ...

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Acked-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 4 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index d3fc3a853..c4db4ca93 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -651,10 +651,7 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 			}
 		}
 		if (old->path && old->name) {
-			char ref_file[PATH_MAX];
-
-			git_snpath(ref_file, sizeof(ref_file), "%s", old->path);
-			if (!file_exists(ref_file) && reflog_exists(old->path))
+			if (!ref_exists(old->path) && reflog_exists(old->path))
 				delete_reflog(old->path);
 		}
 	}