[PATCH 0/2] git describe --first-parent

@@ -25,6 +25,7 @@ static int abbrev = -1; /* unspecified */
 static int max_candidates = 10;
 static struct hash_table names;
 static int have_util;
+static int first_parent;
 static const char *pattern;
 static int always;
 static const char *dirty;

@@ -336,7 +337,7 @@ static void describe(const char *arg, int last_one)
 			if (!(p->object.flags & SEEN))
 				commit_list_insert_by_date(p, &list);
 			p->object.flags |= c->object.flags;
-			parents = parents->next;
+			parents = first_parent ? NULL : parents->next;
 		}
 	}
 

@@ -414,6 +415,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 			   N_("only consider tags matching <pattern>")),
 		OPT_BOOLEAN(0, "always",     &always,
 			   N_("show abbreviated commit object as fallback")),
+		OPT_BOOLEAN(0, "first-parent",     &first_parent,
+			   "follow first parents only"),
 		{OPTION_STRING, 0, "dirty",  &dirty, N_("mark"),
 			   N_("append <mark> on dirty working tree (default: \"-dirty\")"),
 		 PARSE_OPT_OPTARG, NULL, (intptr_t) "-dirty"},

@@ -435,6 +438,9 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 	if (longformat && abbrev == 0)
 		die(_("--long is incompatible with --abbrev=0"));
 
+	if (contains && first_parent)
+		die(_("--contains is incompatible with --first-parent"));
+
 	if (contains) {
 		const char **args = xmalloc((7 + argc) * sizeof(char *));
 		int i = 0;

@@ -84,6 +84,10 @@ OPTIONS
 	Only consider tags matching the given pattern (can be used to avoid
 	leaking private tags made from the repository).
 
+--first-parent::
+	Only consider tags which can be reached from '<committish>' by a first
+	parent walk, i.e. only those which are not on side branches.
+
 --always::
 	Show uniquely abbreviated commit object as fallback.
 

@@ -129,6 +133,14 @@ closest tagname without any suffix:
 	[torvalds@g5 git]$ git describe --abbrev=0 v1.0.5^2
 	tags/v1.0.0
 
+With --first-parent, tags on side branches are not considered:
+
+	$ git describe v1.1.0^
+	v1.0.7-44-ge77f489
+
+	$ git describe --first-parent v1.1.0^
+	v1.0.0-41-ge77f489
+
 Note that the suffix you get if you type these commands today may be
 longer than what Linus saw above when he ran these commands, as your
 git repository may have new commits whose object names begin with

@@ -148,7 +160,9 @@ is found, its name will be output and searching will stop.
 If an exact match was not found, 'git describe' will walk back
 through the commit history to locate an ancestor commit which
 has been tagged.  The ancestor's tag will be output along with an
-abbreviation of the input committish's SHA1.
+abbreviation of the input committish's SHA1.  With '--first-parent',
+'git describe' will walk the history only along the first parent
+of each commit.
 
 If multiple tags were found during the walk then the tag which
 has the fewest commits different from the input committish will be

@@ -103,6 +103,13 @@ check_describe c-* --tags HEAD^^2
 check_describe B --tags HEAD^^2^
 check_describe e --tags HEAD^^^
 
+check_describe R-* --first-parent HEAD
+check_describe R-* --first-parent HEAD^
+check_describe R-* --first-parent HEAD^^
+check_describe B-* --first-parent HEAD^^2
+check_describe B --first-parent HEAD^^2^
+check_describe R-* --first-parent HEAD^^^
+
 check_describe heads/master --all HEAD
 check_describe tags/c-* --all HEAD^
 check_describe tags/e --all HEAD^^^