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Teach git-describe --exact-match to avoid expensive tag searches

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Sometimes scripts want (or need) the annotated tag name that exactly
matches a specific commit, or no tag at all.  In such cases it can be
difficult to determine if the output of `git describe $commit` is a
real tag name or a tag+abbreviated commit.  A common idiom is to run
git-describe twice:

  if test $(git describe $commit) = $(git describe --abbrev=0 $commit)
  ...

but this is a huge waste of time if the caller is just going to pick a
different method to describe $commit or abort because it is not exactly
an annotated tag.

Setting the maximum number of candidates to 0 allows the caller to ask
for only a tag that directly points at the supplied commit, or to have
git-describe abort if no such item exists.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Shawn O. Pearce 2008-02-24 03:07:31 -05:00 committed by Junio C Hamano
parent 8a5a1884e9
commit 2c33f75754
2 changed files with 11 additions and 2 deletions
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5
Documentation/git-describe.txt
View File

@ -45,6 +45,11 @@ OPTIONS
candidates to describe the input committish consider
up to <n> candidates. Increasing <n> above 10 will take
slightly longer but may produce a more accurate result.
An <n> of 0 will cause only exact matches to be output.
--exact-match::
Only output exact matches (a tag directly references the
supplied commit). This is a synonym for --candidates=0.
--debug::
Verbosely display information about the searching strategy

8
builtin-describe.c
View File

@ -174,6 +174,8 @@ static void describe(const char *arg, int last_one)
return;
}
if (!max_candidates)
die("no tag exactly matches '%s'", sha1_to_hex(cmit->object.sha1));
if (debug)
fprintf(stderr, "searching to describe %s\n", arg);
@ -270,6 +272,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
OPT_BOOLEAN(0, "all", &all, "use any ref in .git/refs"),
OPT_BOOLEAN(0, "tags", &tags, "use any tag in .git/refs/tags"),
OPT__ABBREV(&abbrev),
OPT_SET_INT(0, "exact-match", &max_candidates,
"only output exact matches", 0),
OPT_INTEGER(0, "candidates", &max_candidates,
"consider <n> most recent tags (default: 10)"),
OPT_STRING(0, "match", &pattern, "pattern",
@ -278,8 +282,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
};
argc = parse_options(argc, argv, options, describe_usage, 0);
if (max_candidates < 1)
max_candidates = 1;
if (max_candidates < 0)
max_candidates = 0;
else if (max_candidates > MAX_TAGS)
max_candidates = MAX_TAGS;