mp.input: allow async completions

Previously, it was impossible to generate a list of completions for an
`input.get()` request asynchronously, as the values had to be returned
by the callback function.

This commit provides a way to send completions asynchronously by passing
a second argument to the complete callback; a function which can be
passed the return values to respond to the complete event.

DOCS/man/lua.rst

@@ -946,14 +946,21 @@ REPL.
 
     ``complete``
         A callback invoked when the user edits the text or moves the cursor. The
-        first argument is the text before the cursor. The callback should return
-        a table of the string candidate completion values and the 1-based cursor
+        first argument is the text before the cursor, and the second argument is
+        a response function which can be called to present completion values to
+        the user.
+
+        The first argument to the response function is a table of the string
+        candidate completion values, and the second argument is the 1-based cursor
         position from which the completion starts. console will show the
         completions that fuzzily match the text between this position and the
-        cursor and allow selecting them.
+        cursor, which the user can select with ``TAB``. The completions will only
+        be shown to the user if the text before the cursor has not since changed.
+        The response function should be called with an empty table if there are no
+        completion values to display.
 
-        The third and optional return value is a string that will be appended to
-        the input line without displaying it in the completions.
+        The third and optional argument to the response function is a string that
+        will be appended to the input line without displaying it in the completions.
 
     ``autoselect_completion``
         Whether to automatically select the first completion on submit if one

player/javascript/defaults.js

@@ -662,26 +662,33 @@ function register_event_handler(t) {
     latest_handler_id = handler_id;
 
     mp.register_script_message(handler_id, function (type, args) {
-        if (latest_handler_id !== handler_id && type !== "closed")
+        if (type == "closed")
+            mp.unregister_script_message(handler_id);
+
+        if (!t[type] || (latest_handler_id !== handler_id && type !== "closed"))
             return;
 
-        if (t[type]) {
-            args = args ? JSON.parse(args) : [];
-            var result = t[type].apply(null, args);
+        args = args ? JSON.parse(args) : [];
+
+        if (type == "complete") {
+            var complete = function(completions, completion_pos, completion_append) {
+                if (completions == undefined)
+                    return;
 
-            if (type == "complete" && result) {
                 mp.commandv("script-message-to", "console", "complete", JSON.stringify({
                                 client_name: mp.script_name,
                                 handler_id: handler_id,
-                                list: result[0],
-                                start_pos: result[1],
-                                append: result[2] || "",
+                                list: completions,
+                                start_pos: completion_pos,
+                                append: completion_append || "",
                             }));
             }
-        }
 
-        if (type == "closed")
-            mp.unregister_script_message(handler_id);
+            args[1] = complete;
+            complete.apply(null, t[type].apply(null, args));
+        } else {
+            t[type].apply(null, args)
+        }
     })
 
     return handler_id;

player/lua/input.lua

@@ -40,16 +40,23 @@ local function register_event_handler(t)
     latest_handler_id = handler_id
 
     mp.register_script_message(handler_id, function (type, args)
+        if type == "closed" then
+            mp.unregister_script_message(handler_id)
+        end
+
         -- do not process events (other than closed) for an input that has been overwritten
-        if latest_handler_id ~= handler_id and type ~= "closed" then
+        if not t[type] or (latest_handler_id ~= handler_id and type ~= "closed") then
             return
         end
 
-        if t[type] then
-            local completions, completion_pos, completion_append =
-                t[type](unpack(utils.parse_json(args or "") or {}))
+        args = utils.parse_json(args or "") or {}
+
+        if type == "complete" then
+            local function complete(completions, completion_pos, completion_append)
+                if not completions then
+                    return
+                end
 
-            if type == "complete" and completions then
                 mp.commandv("script-message-to", "console", "complete", utils.format_json({
                                 client_name = mp.get_script_name(),
                                 handler_id = handler_id,
@@ -58,10 +65,11 @@ local function register_event_handler(t)
                                 append = completion_append or "",
                             }))
             end
-        end
 
-        if type == "closed" then
-            mp.unregister_script_message(handler_id)
+            args[2] = complete
+            complete(t[type](unpack(args)))
+        else
+            t[type](unpack(args))
         end
     end)