help: respect aliases

If we have an alias "foo" defined, then the help text for
"foo" (via "git help foo" or "git foo --help") now shows the
definition of the alias.

Before showing an alias definition, we make sure that there
is no git command which would override the alias (so that
even though you may have a "log" alias, even though it will
not work, we don't want to it supersede "git help log").

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

help.c

@@ -210,7 +210,7 @@ static unsigned int list_commands_in_dir(struct cmdnames *cmds,
 	return longest;
 }
 
-static void list_commands(void)
+static unsigned int load_command_list(void)
 {
 	unsigned int longest = 0;
 	unsigned int len;
@@ -250,6 +250,14 @@ static void list_commands(void)
 	uniq(&other_cmds);
 	exclude_cmds(&other_cmds, &main_cmds);
 
+	return longest;
+}
+
+static void list_commands(void)
+{
+	unsigned int longest = load_command_list();
+	const char *exec_path = git_exec_path();
+
 	if (main_cmds.cnt) {
 		printf("available git commands in '%s'\n", exec_path);
 		printf("----------------------------");
@@ -284,6 +292,22 @@ void list_common_cmds_help(void)
 	}
 }
 
+static int is_in_cmdlist(struct cmdnames *c, const char *s)
+{
+	int i;
+	for (i = 0; i < c->cnt; i++)
+		if (!strcmp(s, c->names[i]->name))
+			return 1;
+	return 0;
+}
+
+static int is_git_command(const char *s)
+{
+	load_command_list();
+	return is_in_cmdlist(&main_cmds, s) ||
+		is_in_cmdlist(&other_cmds, s);
+}
+
 static const char *cmd_to_page(const char *git_cmd)
 {
 	if (!git_cmd)
@@ -372,6 +396,7 @@ int cmd_version(int argc, const char **argv, const char *prefix)
 int cmd_help(int argc, const char **argv, const char *prefix)
 {
 	int nongit;
+	const char *alias;
 
 	setup_git_directory_gently(&nongit);
 	git_config(git_help_config);
@@ -391,6 +416,12 @@ int cmd_help(int argc, const char **argv, const char *prefix)
 		return 0;
 	}
 
+	alias = alias_lookup(argv[0]);
+	if (alias && !is_git_command(argv[0])) {
+		printf("`git %s' is aliased to `%s'\n", argv[0], alias);
+		return 0;
+	}
+
 	switch (help_format) {
 	case HELP_FORMAT_MAN:
 		show_man_page(argv[0]);