Add a "git-describe" command

From

Linus Torvalds <torvalds@osdl.org>

Date

Dec 24, 2005, 21:50 UTC

Message-ID

<Pine.LNX.4.64.0512241339120.14098@g5.osdl.org>

IOW, with something like Junios current tree, I get:

	[torvalds@g5 git]$ git-describe parent
	refs/tags/v1.0.4-g2414721b

Doing a "git-describe" on a tag-name will just show the full tag path:

	[torvalds@g5 git]$ git-describe v1.0.4
	refs/tags/v1.0.4

This is useful for two things:

 - automatic version naming in Makefiles, for example. We could use it in 
   git itself: when doing "git --version", we could use this to give a 
   much more useful description of exactly what version was installed.

 - for any random commit (say, you use "gitk <pathname>" or 
   "git-whatchanged" to look at what has changed in some file), you can 
   figure out what the last version of the repo was. Ie, say I find a bug 
   in commit 39ca371c45b04cd50d0974030ae051906fc516b6, I just do:

	[torvalds@g5 linux]$ git-describe 39ca371c45b04cd50d0974030ae051906fc516b6
	refs/tags/v2.6.14-rc4-g39ca371c

   and I now know that it was _not_ in v2.6.14-rc4, but was presumably in 
   v2.6.14-rc5.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

Comments?

			Linus

diff --git a/Makefile b/Makefile
index 3395a9e..47e7898 100644
--- a/Makefile
+++ b/Makefile
@@ -135,7 +135,8 @@ PROGRAMS = \
 	git-unpack-objects$X git-update-index$X git-update-server-info$X \
 	git-upload-pack$X git-verify-pack$X git-write-tree$X \
 	git-update-ref$X git-symbolic-ref$X git-check-ref-format$X \
-	git-name-rev$X git-pack-redundant$X git-repo-config$X git-var$X
+	git-name-rev$X git-pack-redundant$X git-repo-config$X git-var$X \
+	git-describe$X
 
 # what 'all' will build and 'install' will install.
 ALL_PROGRAMS = $(PROGRAMS) $(SIMPLE_PROGRAMS) $(SCRIPTS) git$X
diff --git a/describe.c b/describe.c
new file mode 100644
index 0000000..ebfa429
--- /dev/null
+++ b/describe.c
@@ -0,0 +1,118 @@
+#include "cache.h"
+#include "commit.h"
+#include "refs.h"
+
+#define SEEN (1u << 0)
+
+static const char describe_usage[] = "git-describe [--all] <committish>*";
+
+static int all = 0;	/* Default to tags only */
+
+static int names = 0, allocs = 0;
+static struct commit_name {
+	const struct commit *commit;
+	char path[];
+} **name_array = NULL;
+
+static struct commit_name *match(struct commit *cmit)
+{
+	int i = names;
+	struct commit_name **p = name_array;
+
+	while (i-- > 0) {
+		struct commit_name *n = *p++;
+		if (n->commit == cmit)
+			return n;
+	}
+	return NULL;
+}
+
+static void add_to_known_names(const char *path, const struct commit *commit)
+{
+	int idx;
+	int len = strlen(path)+1;
+	struct commit_name *name = xmalloc(sizeof(struct commit_name) + len);
+
+	name->commit = commit;
+	memcpy(name->path, path, len);
+	idx = names;
+	if (idx >= allocs) {
+		allocs = (idx + 50) * 3 / 2;
+		name_array = xrealloc(name_array, allocs*sizeof(*name_array));
+	}
+	name_array[idx] = name;
+	names = ++idx;
+}
+
+static int get_name(const char *path, const unsigned char *sha1)
+{
+	struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+	if (!commit)
+		return 0;
+	if (!all && strncmp(path, "refs/tags/", 10))
+		return 0;
+	add_to_known_names(path, commit);
+	return 0;
+}
+
+static int compare_names(const void *_a, const void *_b)
+{
+	struct commit_name *a = *(struct commit_name **)_a;
+	struct commit_name *b = *(struct commit_name **)_b;
+	unsigned long a_date = a->commit->date;
+	unsigned long b_date = b->commit->date;
+	return (a_date > b_date) ? -1 : (a_date == b_date) ? 0 : 1;
+}
+
+static void describe(struct commit *cmit)
+{
+	struct commit_list *list;
+	static int initialized = 0;
+	struct commit_name *n;
+
+	if (!initialized) {
+		initialized = 1;
+		for_each_ref(get_name);
+		qsort(name_array, names, sizeof(*name_array), compare_names);
+	}
+
+	n = match(cmit);
+	if (n) {
+		printf("%s\n", n->path);
+		return;
+	}
+
+	list = NULL;
+	commit_list_insert(cmit, &list);
+	while (list) {
+		struct commit *c = pop_most_recent_commit(&list, SEEN);
+		n = match(c);
+		if (n) {
+			printf("%s-g%.8s\n", n->path, sha1_to_hex(cmit->object.sha1));
+			return;
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int i;
+
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
+		unsigned char sha1[20];
+		struct commit *cmit;
+
+		if (!strcmp(arg, "--all")) {
+			all = 1;
+			continue;
+		}
+		if (get_sha1(arg, sha1) < 0)
+			usage(describe_usage);
+		cmit = lookup_commit_reference(sha1);
+		if (!cmit)
+			usage(describe_usage);
+		describe(cmit);
+	}
+	return 0;
+}