A string that names an object can be suffixed with ^{type} peeler to
say "I have this object name; peel it until you get this type. If
you cannot do so, it is an error".  v1.8.2^{commit} asks for a commit
that is pointed at an annotated tag v1.8.2; v1.8.2^{tree} unwraps it
further to the top-level tree object.  A special suffix ^{} (i.e. no
type specified) means "I do not care what it unwraps to; just peel
annotated tag until you get something that is not a tag".

When you have a random user-supplied string, you can turn it to a
bare 40-hex object name, and cause it to error out if such an object
does not exist, with:

        git rev-parse --verify "$userstring^{}"

for most objects, but this does not yield the tag object name when
$userstring refers to an annotated tag.

Introduce a new suffix, ^{object}, that only makes sure the given
name refers to an existing object.  Then

        git rev-parse --verify "$userstring^{object}"

becomes a way to make sure $userstring refers to an existing object.

This is necessary because the plumbing "rev-parse --verify" is only
about "make sure the argument is something we can feed to get_sha1()
and turn it into a raw 20-byte object name SHA-1" and is not about
"make sure that 20-byte object name SHA-1 refers to an object that
exists in our object store".  When the given $userstring is already
a 40-hex, by definition "rev-parse --verify $userstring" can turn it
into a raw 20-byte object name.  With "$userstring^{object}", we can
make sure that the 40-hex string names an object that exists in our
object store before "--verify" kicks in.

Signed-off-by: Junio C Hamano <gits...@pobox.com>
 sha1_name.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sha1_name.c b/sha1_name.c
index 45788df..85b6e75 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -594,7 +594,7 @@ struct object *peel_to_type(const char *name, int namelen,
        while (1) {
                if (!o || (!o->parsed && !parse_object(o->sha1)))
                        return NULL;
-               if (o->type == expected_type)
+               if (expected_type == OBJ_ANY || o->type == expected_type)
                        return o;
                if (o->type == OBJ_TAG)
                        o = ((struct tag*) o)->tagged;
@@ -645,6 +645,8 @@ static int peel_onion(const char *name, int len, unsigned 
char *sha1)
                expected_type = OBJ_TREE;
        else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
                expected_type = OBJ_BLOB;
+       else if (!prefixcmp(sp, "object}"))
+               expected_type = OBJ_ANY;
        else if (sp[0] == '}')
                expected_type = OBJ_NONE;
        else if (sp[0] == '/')

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