Teach git-describe how to run name-rev

Often users want to know not which tagged version a commit came
after, but which tagged version a commit is contained within.
This latter task is the job of git-name-rev, but most users are
looking to git-describe to do the job.

Junio suggested we make `git describe --contains` run the correct
tool, `git name-rev`, and that's exactly what we do here.  The output
of name-rev was adjusted slightly through the new --name-only option,
allowing describe to execv into name-rev and maintain its current
output format.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-describe.txt

@@ -8,7 +8,7 @@ git-describe - Show the most recent tag that is reachable from a commit
 
 SYNOPSIS
 --------
-'git-describe' [--all] [--tags] [--abbrev=<n>] <committish>...
+'git-describe' [--all] [--tags] [--contains] [--abbrev=<n>] <committish>...
 
 DESCRIPTION
 -----------
@@ -31,6 +31,11 @@ OPTIONS
 	Instead of using only the annotated tags, use any tag
 	found in `.git/refs/tags`.
 
+--contains::
+	Instead of finding the tag that predates the commit, find
+	the tag that comes after the commit, and thus contains it.
+	Automatically implies --tags.
+
 --abbrev=<n>::
 	Instead of using the default 8 hexadecimal digits as the
 	abbreviated object name, use <n> digits.

Documentation/git-name-rev.txt

@@ -34,6 +34,13 @@ OPTIONS
 	Read from stdin, append "(<rev_name>)" to all sha1's of nameable
 	commits, and pass to stdout
 
+--name-only::
+	Instead of printing both the SHA-1 and the name, print only
+	the name.  If given with --tags the usual tag prefix of
+	"tags/" is also ommitted from the name, matching the output
+	of gitlink::git-describe[1] more closely.  This option
+	cannot be combined with --stdin.
+
 EXAMPLE
 -------
 

builtin-describe.c

@@ -3,6 +3,7 @@
 #include "tag.h"
 #include "refs.h"
 #include "builtin.h"
+#include "exec_cmd.h"
 
 #define SEEN		(1u<<0)
 #define MAX_TAGS	(FLAG_BITS - 1)
@@ -242,12 +243,15 @@ static void describe(const char *arg, int last_one)
 int cmd_describe(int argc, const char **argv, const char *prefix)
 {
 	int i;
+	int contains = 0;
 
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 
 		if (*arg != '-')
 			break;
+		else if (!strcmp(arg, "--contains"))
+			contains = 1;
 		else if (!strcmp(arg, "--debug"))
 			debug = 1;
 		else if (!strcmp(arg, "--all"))
@@ -272,6 +276,16 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 
 	save_commit_buffer = 0;
 
+	if (contains) {
+		const char **args = xmalloc((4 + argc - i) * sizeof(char*));
+		args[0] = "name-rev";
+		args[1] = "--name-only";
+		args[2] = "--tags";
+		memcpy(args + 3, argv + i, (argc - i) * sizeof(char*));
+		args[3 + argc - i] = NULL;
+		return cmd_name_rev(3 + argc - i, args, prefix);
+	}
+
 	if (argc <= i)
 		describe("HEAD", 1);
 	else

builtin-name-rev.c

@@ -83,6 +83,7 @@ copy_data:
 
 struct name_ref_data {
 	int tags_only;
+	int name_only;
 	const char *ref_filter;
 };
 
@@ -110,6 +111,10 @@ static int name_ref(const char *path, const unsigned char *sha1, int flags, void
 
 		if (!prefixcmp(path, "refs/heads/"))
 			path = path + 11;
+		else if (data->tags_only
+		    && data->name_only
+		    && !prefixcmp(path, "refs/tags/"))
+			path = path + 10;
 		else if (!prefixcmp(path, "refs/"))
 			path = path + 5;
 
@@ -149,7 +154,7 @@ int cmd_name_rev(int argc, const char **argv, const char *prefix)
 {
 	struct object_array revs = { 0, 0, NULL };
 	int as_is = 0, all = 0, transform_stdin = 0;
-	struct name_ref_data data = { 0, NULL };
+	struct name_ref_data data = { 0, 0, NULL };
 
 	git_config(git_default_config);
 
@@ -165,6 +170,9 @@ int cmd_name_rev(int argc, const char **argv, const char *prefix)
 			if (!strcmp(*argv, "--")) {
 				as_is = 1;
 				continue;
+			} else if (!strcmp(*argv, "--name-only")) {
+				data.name_only = 1;
+				continue;
 			} else if (!strcmp(*argv, "--tags")) {
 				data.tags_only = 1;
 				continue;
@@ -263,14 +271,17 @@ int cmd_name_rev(int argc, const char **argv, const char *prefix)
 			struct object * obj = get_indexed_object(i);
 			if (!obj)
 				continue;
-			printf("%s %s\n", sha1_to_hex(obj->sha1), get_rev_name(obj));
+			if (!data.name_only)
+				printf("%s ", sha1_to_hex(obj->sha1));
+			printf("%s\n", get_rev_name(obj));
 		}
 	} else {
 		int i;
-		for (i = 0; i < revs.nr; i++)
-			printf("%s %s\n",
-				revs.objects[i].name,
-				get_rev_name(revs.objects[i].item));
+		for (i = 0; i < revs.nr; i++) {
+			if (!data.name_only)
+				printf("%s ", revs.objects[i].name);
+			printf("%s\n", get_rev_name(revs.objects[i].item));
+		}
 	}
 
 	return 0;