for-each-ref: report broken references correctly

If there is a loose reference file with invalid contents, "git
for-each-ref" incorrectly reports the problem as being a missing
object with name NULL_SHA1:

    $ echo '12345678' >.git/refs/heads/nonsense
    $ git for-each-ref
    fatal: missing object 0000000000000000000000000000000000000000 for refs/heads/nonsense

With an explicit "--format" string, it can even report that the
reference validly points at NULL_SHA1:

    $ git for-each-ref --format='%(objectname) %(refname)'
    0000000000000000000000000000000000000000 refs/heads/nonsense
    $ echo $?
    0

This has been broken since

    b7dd2d2 for-each-ref: Do not lookup objects when they will not be used (2009-05-27)

, which changed for-each-ref from using for_each_ref() to using
git_for_each_rawref() in order to avoid looking up the referred-to
objects unnecessarily. (When "git for-each-ref" is given a "--format"
string that doesn't include information about the pointed-to object,
it does not look up the object at all, which makes it considerably
faster. Iterating with DO_FOR_EACH_INCLUDE_BROKEN is essential to this
optimization because otherwise for_each_ref() would itself need to
check whether the object exists as part of its brokenness test.)

But for_each_rawref() includes broken references in the iteration, and
"git for-each-ref" doesn't itself reject references with REF_ISBROKEN.
The result is that broken references are processed *as if* they had
the value NULL_SHA1, which is the value stored in entries for broken
references.

Change "git for-each-ref" to emit warnings for references that are
REF_ISBROKEN but to otherwise skip them.

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

1 files changed, 5 insertions, 0 deletions

diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index 008513c2f1..4a15f568f1 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -851,6 +851,11 @@ static int grab_single_ref(const char *refname, const unsigned char *sha1, int f
 		  return 0;
 	}
 
+	if (flag & REF_ISBROKEN) {
+		  warning("ignoring broken ref %s", refname);
+		  return 0;
+	}
+
 	if (*cb->grab_pattern) {
 		const char **pattern;
 		int namelen = strlen(refname);