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pack-refs: add fully-peeled trait

Older versions of pack-refs did not write peel lines for
refs outside of refs/tags. This meant that on reading the
pack-refs file, we might set the REF_KNOWS_PEELED flag for
such a ref, even though we do not know anything about its
peeled value.

The previous commit updated the writer to always peel, no
matter what the ref is. That means that packed-refs files
written by newer versions of git are fine to be read by both
old and new versions of git. However, we still have the
problem of reading packed-refs files written by older
versions of git, or by other implementations which have not
yet learned the same trick.

The simplest fix would be to always unset the
REF_KNOWS_PEELED flag for refs outside of refs/tags that do
not have a peel line (if it has a peel line, we know it is
valid, but we cannot assume a missing peel line means
anything). But that loses an important optimization, as
upload-pack should not need to load the object pointed to by
refs/heads/foo to determine that it is not a tag.

Instead, we add a "fully-peeled" trait to the packed-refs
file. If it is set, we know that we can trust a missing peel
line to mean that a ref cannot be peeled. Otherwise, we fall
back to assuming nothing.

[commit message and tests by Jeff King <peff@peff.net>]

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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1 parent 03a8edd commit c29c46fa2e21e608ce2e603649af5bf38e7969c2 @mhagger mhagger committed with gitster Mar 18, 2013
Showing with 67 additions and 6 deletions.
  1. +1 −1 pack-refs.c
  2. +44 −5 refs.c
  3. +22 −0 t/t3211-peel-ref.sh
View
@@ -128,7 +128,7 @@ int pack_refs(unsigned int flags)
die_errno("unable to create ref-pack file structure");
/* perhaps other traits later as well */
- fprintf(cbdata.refs_file, "# pack-refs with: peeled \n");
+ fprintf(cbdata.refs_file, "# pack-refs with: peeled fully-peeled \n");
for_each_ref(handle_one_ref, &cbdata);
if (ferror(cbdata.refs_file))
View
49 refs.c
@@ -804,11 +804,38 @@ static const char *parse_ref_line(char *line, unsigned char *sha1)
return line;
}
+/*
+ * Read f, which is a packed-refs file, into dir.
+ *
+ * A comment line of the form "# pack-refs with: " may contain zero or
+ * more traits. We interpret the traits as follows:
+ *
+ * No traits:
+ *
+ * Probably no references are peeled. But if the file contains a
+ * peeled value for a reference, we will use it.
+ *
+ * peeled:
+ *
+ * References under "refs/tags/", if they *can* be peeled, *are*
+ * peeled in this file. References outside of "refs/tags/" are
+ * probably not peeled even if they could have been, but if we find
+ * a peeled value for such a reference we will use it.
+ *
+ * fully-peeled:
+ *
+ * All references in the file that can be peeled are peeled.
+ * Inversely (and this is more important), any references in the
+ * file for which no peeled value is recorded is not peelable. This
+ * trait should typically be written alongside "peeled" for
+ * compatibility with older clients, but we do not require it
+ * (i.e., "peeled" is a no-op if "fully-peeled" is set).
+ */
static void read_packed_refs(FILE *f, struct ref_dir *dir)
{
struct ref_entry *last = NULL;
char refline[PATH_MAX];
- int flag = REF_ISPACKED;
+ enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
while (fgets(refline, sizeof(refline), f)) {
unsigned char sha1[20];
@@ -817,24 +844,36 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
if (!strncmp(refline, header, sizeof(header)-1)) {
const char *traits = refline + sizeof(header) - 1;
- if (strstr(traits, " peeled "))
- flag |= REF_KNOWS_PEELED;
+ if (strstr(traits, " fully-peeled "))
+ peeled = PEELED_FULLY;
+ else if (strstr(traits, " peeled "))
+ peeled = PEELED_TAGS;
/* perhaps other traits later as well */
continue;
}
refname = parse_ref_line(refline, sha1);
if (refname) {
- last = create_ref_entry(refname, sha1, flag, 1);
+ last = create_ref_entry(refname, sha1, REF_ISPACKED, 1);
+ if (peeled == PEELED_FULLY ||
+ (peeled == PEELED_TAGS && !prefixcmp(refname, "refs/tags/")))
+ last->flag |= REF_KNOWS_PEELED;
add_ref(dir, last);
continue;
}
if (last &&
refline[0] == '^' &&
strlen(refline) == 42 &&
refline[41] == '\n' &&
- !get_sha1_hex(refline + 1, sha1))
+ !get_sha1_hex(refline + 1, sha1)) {
hashcpy(last->u.value.peeled, sha1);
+ /*
+ * Regardless of what the file header said,
+ * we definitely know the value of *this*
+ * reference:
+ */
+ last->flag |= REF_KNOWS_PEELED;
+ }
}
}
View
@@ -39,4 +39,26 @@ test_expect_success 'refs are peeled outside of refs/tags (packed)' '
test_cmp expect actual
'
+test_expect_success 'create old-style pack-refs without fully-peeled' '
+ # Git no longer writes without fully-peeled, so we just write our own
+ # from scratch; we could also munge the existing file to remove the
+ # fully-peeled bits, but that seems even more prone to failure,
+ # especially if the format ever changes again. At least this way we
+ # know we are emulating exactly what an older git would have written.
+ {
+ echo "# pack-refs with: peeled " &&
+ print_ref "refs/heads/master" &&
+ print_ref "refs/outside/foo" &&
+ print_ref "refs/tags/base" &&
+ print_ref "refs/tags/foo" &&
+ echo "^$(git rev-parse "refs/tags/foo^{}")"
+ } >tmp &&
+ mv tmp .git/packed-refs
+'
+
+test_expect_success 'refs are peeled outside of refs/tags (old packed)' '
+ git show-ref -d >actual &&
+ test_cmp expect actual
+'
+
test_done

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