Add command completion with tab key

In the command prompt, press <tab> to get a list of all available
commands and pick one (using vis-menu). This works also after typing the
first letters of a command (p.e. `:la<tab>`).

Co-authored-by: Matěj Cepl <mcepl@cepl.eu>

1 files changed, 36 insertions, 0 deletions

diff --git a/vis-lua.c b/vis-lua.c
index 695ebdb..99d9746 100644
--- a/vis-lua.c
+++ b/vis-lua.c
@@ -1147,6 +1147,41 @@ static int command_register(lua_State *L) {
 }
 
 /***
+ * Let user pick a command matching the given prefix.
+ *
+ * The editor core will be blocked while the external process is running.
+ *
+ * @function complete_command
+ * @tparam string prefix the prefix of the command to be completed
+ * @treturn int code the exit status of the executed command
+ * @treturn string stdout the data written to stdout
+ * @treturn string stderr the data written to stderr
+ */
+static int complete_command(lua_State *L) {
+	Vis *vis = obj_ref_check(L, 1, "vis");
+	const char *prefix = luaL_checkstring(L, 2);
+	char *out = NULL, *err = NULL;
+	char cmd[32];
+	int max_prefix_len = sizeof(cmd) - sizeof("grep '^' | vis-menu -b"); // including NUL
+	snprintf(cmd, sizeof(cmd), "grep '^%.*s' | vis-menu -b", max_prefix_len, prefix);
+
+	Buffer buf = {0};
+	vis_print_cmds(vis, &buf);
+	int status = vis_pipe_buf_collect(vis, buffer_content0(&buf), (const char*[]){cmd, NULL}, &out, &err, false);
+
+	lua_pushinteger(L, status);
+	if (out) lua_pushstring(L, out);
+	else     lua_pushnil(L);
+	if (err) lua_pushstring(L, err);
+	else     lua_pushnil(L);
+
+	free(out);
+	free(err);
+	buffer_release(&buf);
+	return 3;
+}
+
+/***
  * Push keys to input queue and interpret them.
  *
  * The keys are processed as if they were read from the keyboard.
@@ -1559,6 +1594,7 @@ static const struct luaL_Reg vis_lua[] = {
 	{ "option_register", option_register },
 	{ "option_unregister", option_unregister },
 	{ "command_register", command_register },
+	{ "complete_command", complete_command },
 	{ "feedkeys", feedkeys },
 	{ "insert", insert },
 	{ "replace", replace },