pretty: add merge and exclude options to %(describe)

Allow restricting the tags used by the placeholder %(describe) with the
options match and exclude.  E.g. the following command describes the
current commit using official version tags, without those for release
candidates:

   $ git log -1 --format='%(describe:match=v[0-9]*,exclude=*rc*)'

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/Documentation/pretty-formats.txt b/Documentation/pretty-formats.txt
index bb8c05bc21..231010e6ef 100644
--- a/Documentation/pretty-formats.txt
+++ b/Documentation/pretty-formats.txt
@@ -208,8 +208,17 @@ The placeholders are:
 '%cs':: committer date, short format (`YYYY-MM-DD`)
 '%d':: ref names, like the --decorate option of linkgit:git-log[1]
 '%D':: ref names without the " (", ")" wrapping.
-'%(describe)':: human-readable name, like linkgit:git-describe[1];
-		empty string for undescribable commits
+'%(describe[:options])':: human-readable name, like
+			  linkgit:git-describe[1]; empty string for
+			  undescribable commits.  The `describe` string
+			  may be followed by a colon and zero or more
+			  comma-separated options.
++
+** 'match=<pattern>': Only consider tags matching the given
+   `glob(7)` pattern, excluding the "refs/tags/" prefix.
+** 'exclude=<pattern>': Do not consider tags matching the given
+   `glob(7)` pattern, excluding the "refs/tags/" prefix.
+
 '%S':: ref name given on the command line by which the commit was reached
        (like `git log --source`), only works with `git log`
 '%e':: encoding