describe: teach describe negative pattern matches

Teach git-describe the `--exclude` option which will allow specifying
a glob pattern of tags to ignore. This can be combined with the
`--match` patterns to enable more flexibility in determining which tags
to consider.

For example, suppose you wish to find the first official release tag
that contains a certain commit. If we assume that official release tags
are of the form "v*" and pre-release candidates include "*rc*" in their
name, we can now find the first release tag that introduces the commit
abcdef:

  git describe --contains --match="v*" --exclude="*rc*" abcdef

Add documentation, tests, and completion for this change.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/git-describe.txt b/Documentation/git-describe.txt
index 7ad41e2..8755f3a 100644
--- a/Documentation/git-describe.txt
+++ b/Documentation/git-describe.txt
@@ -88,6 +88,16 @@ OPTIONS
 	patterns will be considered. Use `--no-match` to clear and reset the
 	list of patterns.
 
+--exclude <pattern>::
+	Do not consider tags matching the given `glob(7)` pattern, excluding
+	the "refs/tags/" prefix. This can be used to narrow the tag space and
+	find only tags matching some meaningful criteria. If given multiple
+	times, a list of patterns will be accumulated and tags matching any
+	of the patterns will be excluded. When combined with --match a tag will
+	be considered when it matches at least one --match pattern and does not
+	match any of the --exclude patterns. Use `--no-exclude` to clear and
+	reset the list of patterns.
+
 --always::
 	Show uniquely abbreviated commit object as fallback.