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>`).

lua/plugins/complete-filename.lua

@@ -22,9 +22,19 @@ local complete_filename = function(expand)
  range.finish = pos
  end
 
- local cmdfmt = "vis-complete --file '%s'"
- if expand then cmdfmt = "vis-open -- '%s'*" end
- local status, out, err = vis:pipe(cmdfmt:format(prefix:gsub("'", "'\\''")))
+ local status, out, err
+ if prefix:sub(1, 1) == ":" then
+ status, out, err = vis:complete_command(prefix:sub(2))
+ if out then
+ out = out:gsub("\n$", ""):sub(#prefix) .. " "
+ end
+ pos = range.start + #prefix
+ expand = false
+ else
+ local cmdfmt = "vis-complete --file '%s'"
+ if expand then cmdfmt = "vis-open -- '%s'*" end
+ status, out, err = vis:pipe(cmdfmt:format(prefix:gsub("'", "'\\''")))
+ end
  if status ~= 0 or not out then
  if err then vis:info(err) end
  return
@@ -48,4 +58,4 @@ end, "Complete file name")
 -- complete file path at primary selection location using vis-open(1)
 vis:map(vis.modes.INSERT, "<C-x><C-o>", function()
  complete_filename(true);
-end, "Complete file name (expands path)")
+end, "Complete file name (expands path) or command")

vis-cmds.c

@@ -698,6 +698,19 @@ static bool print_cmd(const char *key, void *value, void *data) {
  return text_appendf(data, " %-30s %s\n", usage, help ? help : "");
 }
 
+static bool print_cmd_name(const char *key, void *value, void *data) {
+ CommandDef *cmd = value;
+ size_t len_data = strlen(data);
+ size_t remaining_capacity = VIS_COMMAND_BUFFER_MAX - len_data;
+ if (remaining_capacity >= strlen(cmd->name) + 2) /* adding 2 for \n and \0 */
+ snprintf(data + len_data, remaining_capacity, "%s\n", cmd->name);
+ return true;
+}
+
+void vis_print_cmds(Vis *vis, char *cmd_list) {
+ map_iterate(vis->cmds, print_cmd_name, cmd_list);
+}
+
 static bool print_option(const char *key, void *value, void *txt) {
  char desc[256];
  const OptionDef *opt = value;

vis-lua.c

@@ -1252,6 +1252,44 @@ static int command_register(lua_State *L) {
  return 1;
 }
 
+/***
+ * 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;
+ File *file = vis->win ? vis->win->file : NULL;
+ Filerange range = text_range_new(0, 0);
+
+ char cmd_list[VIS_COMMAND_BUFFER_MAX] = {0};
+ vis_print_cmds(vis, cmd_list);
+ char cmd[VIS_COMMAND_BUFFER_MAX + 32] = {0}; /* 32 for echo/grep/vis-menu */
+ sprintf(cmd, "echo '%s' | grep '^%s' | vis-menu -b", cmd_list, prefix);
+
+ int status = vis_pipe_collect(vis, file, &range, (const char*[]){ cmd, NULL }, &out, &err, false);
+ lua_pushinteger(L, status);
+ if (out)
+ lua_pushstring(L, out);
+ else
+ lua_pushnil(L);
+ free(out);
+ if (err)
+ lua_pushstring(L, err);
+ else
+ lua_pushnil(L);
+ free(err);
+ return 3;
+}
+
 /***
  * Push keys to input queue and interpret them.
  *
@@ -1638,6 +1676,7 @@ 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 },

vis.h

@@ -40,6 +40,9 @@ typedef struct Win Win;
 /* maximum bytes needed for string representation of a (pseudo) key */
 #define VIS_KEY_LENGTH_MAX 64
 
+/* maximum bytes used for list of available commands */
+#define VIS_COMMAND_BUFFER_MAX 1000
+
 /**
  * Editor event handlers.
  */
@@ -895,6 +898,9 @@ bool vis_option_unregister(Vis*, const char *name);
 /** Execute any kind (``:``, ``?``, ``/``) of prompt command */
 bool vis_prompt_cmd(Vis*, const char *cmd);
 
+/** Write newline separated list of available commands to ``cmd_list`` */
+void vis_print_cmds(Vis*, char *cmd_list);
+
 /**
  * Pipe a given file range to an external process.
  *