[GSoC][PATCH 3/6 v2] submodule: port set_name_rev from shell to C

[Prathamesh Chavan <pc44800@gmail.com>]

Since later on we want to port submodule subcommand status, and since
set_name_rev is part of cmd_status, hence this function is ported. It
has been ported to function print_name_rev in C, which calls get_name_rev
to get the revname, and after formatting it, print_name_rev prints it.
And hence in this way, the command `git submodule--helper print-name-rev
"sm_path" "sha1"` sets value of revname in git-submodule.sh

The function get_name_rev returns the stdout of the git describe
commands. Since there are four different git-describe commands used for
generating the name rev, four child_process are introduced, each successive
child process running only when previous has no stdout. The order of these
four git-describe commands is maintained the same as it was in the function
set_name_rev() in shell script.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Prathamesh Chavan <pc44800@gmail.com>
---
 builtin/submodule--helper.c | 69 +++++++++++++++++++++++++++++++++++++++++++++
 git-submodule.sh            | 16 ++---------
 2 files changed, 71 insertions(+), 14 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 5180659fd..86112ac92 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -244,6 +244,74 @@ static char *get_submodule_displaypath(const char *path, const char *prefix)
 	}
 }
 
+enum describe_step {
+	step_bare,
+	step_tags,
+	step_contains,
+	step_all_always,
+	step_end
+};
+
+static char *get_name_rev(const char *sub_path, const char* object_id)
+{
+	struct strbuf sb = STRBUF_INIT;
+	enum describe_step cur_step;
+
+	for (cur_step = step_bare; cur_step < step_end; cur_step++) {
+		struct child_process cp = CHILD_PROCESS_INIT;
+		prepare_submodule_repo_env(&cp.env_array);
+		cp.dir = sub_path;
+		cp.git_cmd = 1;
+		cp.no_stderr = 1;
+
+		switch (cur_step) {
+			case step_bare:
+				argv_array_pushl(&cp.args, "describe",
+						 object_id, NULL);
+				break;
+			case step_tags:	
+				argv_array_pushl(&cp.args, "describe",
+						 "--tags", object_id, NULL);
+				break;
+			case step_contains:
+				argv_array_pushl(&cp.args, "describe",
+						 "--contains", object_id,
+						 NULL);
+				break;
+			case step_all_always:
+				argv_array_pushl(&cp.args, "describe",
+						 "--all", "--always",
+						 object_id, NULL);
+				break;
+			default:
+				BUG("unknown describe step '%d'", cur_step);
+		}
+
+		if (!capture_command(&cp, &sb, 0) && sb.len) {
+			strbuf_strip_suffix(&sb, "\n");
+			return strbuf_detach(&sb, NULL);
+		}
+
+	}
+
+	strbuf_release(&sb);
+	return NULL;
+}
+
+static int print_name_rev(int argc, const char **argv, const char *prefix)
+{
+	char *namerev;
+	if (argc != 3)
+		die("print-name-rev only accepts two arguments: <path> <sha1>");
+
+	namerev = get_name_rev(argv[1], argv[2]);
+	if (namerev && namerev[0])
+		printf(" (%s)", namerev);
+	printf("\n");
+
+	return 0;
+}
+
 struct module_list {
 	const struct cache_entry **entries;
 	int alloc, nr;
@@ -1405,6 +1473,7 @@ static struct cmd_struct commands[] = {
 	{"resolve-relative-url", resolve_relative_url, 0},
 	{"resolve-relative-url-test", resolve_relative_url_test, 0},
 	{"foreach", module_foreach, SUPPORT_SUPER_PREFIX},
+	{"print-name-rev", print_name_rev, 0},
 	{"init", module_init, SUPPORT_SUPER_PREFIX},
 	{"remote-branch", resolve_remote_submodule_branch, 0},
 	{"push-check", push_check, 0},
diff --git a/git-submodule.sh b/git-submodule.sh
index c88e0ff7e..b28a6ba8e 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -722,18 +722,6 @@ cmd_update()
 	}
 }
 
-set_name_rev () {
-	revname=$( (
-		sanitize_submodule_env
-		cd "$1" && {
-			git describe "$2" 2>/dev/null ||
-			git describe --tags "$2" 2>/dev/null ||
-			git describe --contains "$2" 2>/dev/null ||
-			git describe --all --always "$2"
-		}
-	) )
-	test -z "$revname" || revname=" ($revname)"
-}
 #
 # Show commit summary for submodules in index or working tree
 #
@@ -1005,14 +993,14 @@ cmd_status()
 		fi
 		if git diff-files --ignore-submodules=dirty --quiet -- "$sm_path"
 		then
-			set_name_rev "$sm_path" "$sha1"
+			revname=$(git submodule--helper print-name-rev "$sm_path" "$sha1")
 			say " $sha1 $displaypath$revname"
 		else
 			if test -z "$cached"
 			then
 				sha1=$(sanitize_submodule_env; cd "$sm_path" && git rev-parse --verify HEAD)
 			fi
-			set_name_rev "$sm_path" "$sha1"
+			revname=$(git submodule--helper print-name-rev "$sm_path" "$sha1")
 			say "+$sha1 $displaypath$revname"
 		fi
 
-- 
2.13.0