completion: implement and use --list-cmds=main,others

This is part of the effort to break down and provide commands by
category in machine-readable form. This could be helpful later on when
completion script switches to use --list-cmds for selecting
completable commands. It would be much easier for the user to choose
to complete _all_ commands instead of the default selection by passing
different values to --list-cmds in git-completino.bash.

While at there, replace "git help -a" in git-completion.bash with
--list-cmds since it's better suited for this task.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git.txt

@@ -167,7 +167,8 @@ foo.bar= ...`) sets `foo.bar` to the empty string which `git config
 	List commands by group. This is an internal/experimental
 	option and may change or be removed in the future. Supported
 	groups are: builtins, parseopt (builtin commands that use
-	parse-options).
+	parse-options), main (all commands in libexec directory),
+	others (all other commands in `$PATH` that have git- prefix).
 
 GIT COMMANDS
 ------------

contrib/completion/git-completion.bash

@@ -839,7 +839,7 @@ __git_commands () {
 	then
 		printf "%s" "${GIT_TESTING_COMMAND_COMPLETION}"
 	else
-		git help -a|egrep '^  [a-zA-Z0-9]'
+		git --list-cmds=main,others
 	fi
 }
 

git.c

@@ -56,6 +56,10 @@ static int list_cmds(const char *spec)
 
 		if (match_token(spec, len, "builtins"))
 			list_builtins(&list, 0);
+		else if (match_token(spec, len, "main"))
+			list_all_main_cmds(&list);
+		else if (match_token(spec, len, "others"))
+			list_all_other_cmds(&list);
 		else
 			die(_("unsupported command listing type '%s'"), spec);
 		spec += len;

help.c

@@ -297,6 +297,38 @@ void list_common_cmds_help(void)
 	print_cmd_by_category(common_categories);
 }
 
+void list_all_main_cmds(struct string_list *list)
+{
+	struct cmdnames main_cmds, other_cmds;
+	int i;
+
+	memset(&main_cmds, 0, sizeof(main_cmds));
+	memset(&other_cmds, 0, sizeof(other_cmds));
+	load_command_list("git-", &main_cmds, &other_cmds);
+
+	for (i = 0; i < main_cmds.cnt; i++)
+		string_list_append(list, main_cmds.names[i]->name);
+
+	clean_cmdnames(&main_cmds);
+	clean_cmdnames(&other_cmds);
+}
+
+void list_all_other_cmds(struct string_list *list)
+{
+	struct cmdnames main_cmds, other_cmds;
+	int i;
+
+	memset(&main_cmds, 0, sizeof(main_cmds));
+	memset(&other_cmds, 0, sizeof(other_cmds));
+	load_command_list("git-", &main_cmds, &other_cmds);
+
+	for (i = 0; i < other_cmds.cnt; i++)
+		string_list_append(list, other_cmds.names[i]->name);
+
+	clean_cmdnames(&main_cmds);
+	clean_cmdnames(&other_cmds);
+}
+
 int is_in_cmdlist(struct cmdnames *c, const char *s)
 {
 	int i;

help.h

@@ -1,6 +1,8 @@
 #ifndef HELP_H
 #define HELP_H
 
+struct string_list;
+
 struct cmdnames {
 	int alloc;
 	int cnt;
@@ -17,6 +19,8 @@ static inline void mput_char(char c, unsigned int num)
 }
 
 extern void list_common_cmds_help(void);
+extern void list_all_main_cmds(struct string_list *list);
+extern void list_all_other_cmds(struct string_list *list);
 extern const char *help_unknown_cmd(const char *cmd);
 extern void load_command_list(const char *prefix,
 			      struct cmdnames *main_cmds,