peel_onion(): add support for <rev>^{tag}

Complete the <rev>^{<type>} family of object descriptors by having
<rev>^{tag} dereference <rev> until a tag object is found (or fail if
unable).

At first glance this may not seem very useful, as commits, trees, and
blobs cannot be peeled to a tag, and a tag would just peel to itself.
However, this can be used to ensure that <rev> names a tag object:

    $ git rev-parse --verify v1.8.4^{tag}
    04f013dc38d7512eadb915eba22efc414f18b869
    $ git rev-parse --verify master^{tag}
    error: master^{tag}: expected tag type, but the object dereferences to tree type
    fatal: Needed a single revision

Users can already ensure that <rev> is a tag object by checking the
output of 'git cat-file -t <rev>', but:
  * users may expect <rev>^{tag} to exist given that <rev>^{commit},
    <rev>^{tree}, and <rev>^{blob} all exist
  * this syntax is more convenient/natural in some circumstances

Signed-off-by: Richard Hansen <rhansen@bbn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index d477b3f6bcb2c410952b573421d28189d1d1a790..b3322adf24880d95c502869097aca29eb4637776 100644 (file)
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -121,6 +121,9 @@ some output processing may assume ref names in UTF-8.
 object that exists, without requiring 'rev' to be a tag, and
 without dereferencing 'rev'; because a tag is already an object,
 it does not have to be dereferenced even once to get to an object.
++
+'rev{caret}\{tag\}' can be used to ensure that 'rev' identifies an
+existing tag object.
 
 '<rev>{caret}\{\}', e.g. 'v0.99.8{caret}\{\}'::
   A suffix '{caret}' followed by an empty brace pair

diff --git a/sha1_name.c b/sha1_name.c
index 65ad066d9bb4efd9b61142b40d790bac9543de1d..6dc496deb002c553dd48295949ac19bf08b0cb8e 100644 (file)
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -679,6 +679,8 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
        sp++; /* beginning of type name, or closing brace for empty */
        if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
                expected_type = OBJ_COMMIT;
+       else if (!strncmp(tag_type, sp, 3) && sp[3] == '}')
+               expected_type = OBJ_TAG;
        else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
                expected_type = OBJ_TREE;
        else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')

diff --git a/t/t1511-rev-parse-caret.sh b/t/t1511-rev-parse-caret.sh
index eaefc777bd98aeb4cae2ba34eec0e5fe2c2fbd72..15973f20945769fd7661cd4b203e96032495a60e 100755 (executable)
--- a/t/t1511-rev-parse-caret.sh
+++ b/t/t1511-rev-parse-caret.sh
@@ -54,6 +54,13 @@ test_expect_success 'ref^{tree}' '
        test_must_fail git rev-parse blob-tag^{tree}
 '
 
+test_expect_success 'ref^{tag}' '
+       test_must_fail git rev-parse HEAD^{tag} &&
+       git rev-parse commit-tag >expected &&
+       git rev-parse commit-tag^{tag} >actual &&
+       test_cmp expected actual
+'
+
 test_expect_success 'ref^{/.}' '
        git rev-parse master >expected &&
        git rev-parse master^{/.} >actual &&