input: add key name to script-binding command response

The "script-binding" command is used by the Lua scripting wrapper to
register key bindings on the fly. It's also the only way to get fine-
grained information about key events (such as separate key up/down
events). This information is sent via a "key-binding" message when the
state of a key changes.

Extend it to send name of the mapped key itself. Previously, it was
assumed that the user just uses an unique identifier for the binding's
name, so it wasn't needed. With this change, a user can map exactly the
same command to multiple keys, which is useful especially with the next
commit.

Part of #2612.

DOCS/man/input.rst

@@ -647,14 +647,20 @@ Input Commands that are Possibly Subject to Change
     For completeness, here is how this command works internally. The details
     could change any time. On any matching key event, ``script_message_to``
     or ``script_message`` is called (depending on whether the script name is
-    included), where the first argument is the string ``key-binding``, the
-    second argument is the name of the binding, and the third argument is the
-    key state as string. The key state consists of a number of letters. The
-    first letter is one of ``d`` (key was pressed down), ``u`` (was released),
-    ``r`` (key is still down, and was repeated; only if key repeat is enabled
-    for this binding), ``p`` (key was pressed; happens if up/down can't be
-    tracked). The second letter whether the event originates from the mouse,
-    either ``m`` (mouse button) or ``-`` (something else).
+    included), with the following arguments:
+
+    1. The string ``key-binding``.
+    2. The name of the binding (as established above).
+    3. The key state as string (see below).
+    4. The key name (since mpv 0.15.0).
+
+    The key state consists of 2 letters:
+
+    1. One of ``d`` (key was pressed down), ``u`` (was released), ``r`` (key
+       is still down, and was repeated; only if key repeat is enabled for this
+       binding), ``p`` (key was pressed; happens if up/down can't be tracked).
+    2. Whether the event originates from the mouse, either ``m`` (mouse button)
+       or ``-`` (something else).
 
 ``ab-loop``
     Cycle through A-B loop states. The first command will set the ``A`` point

input/cmd_parse.c

@@ -417,6 +417,7 @@ mp_cmd_t *mp_cmd_clone(mp_cmd_t *cmd)
         m_option_copy(ret->args[i].type, &ret->args[i].v, &cmd->args[i].v);
     }
     ret->original = bstrdup(ret, cmd->original);
+    ret->key_name = talloc_strdup(ret, ret->key_name);
 
     if (cmd->id == MP_CMD_COMMAND_LIST) {
         struct mp_cmd *prev = NULL;

input/input.c

@@ -460,11 +460,10 @@ static mp_cmd_t *get_cmd_from_keys(struct input_ctx *ictx, char *force_section,
     mp_cmd_t *ret = mp_input_parse_cmd(ictx, bstr0(cmd->cmd), cmd->location);
     if (ret) {
         ret->input_section = cmd->owner->section;
+        ret->key_name = talloc_steal(ret, mp_input_get_key_combo_name(&code, 1));
         if (mp_msg_test(ictx->log, MSGL_DEBUG)) {
-            char *keyname = mp_input_get_key_combo_name(&code, 1);
             MP_DBG(ictx, "key '%s' -> '%s' in '%s'\n",
-                   keyname, cmd->cmd, ret->input_section);
-            talloc_free(keyname);
+                   ret->key_name, cmd->cmd, ret->input_section);
         }
         ret->is_mouse_button = code & MP_KEY_EMIT_ON_UP;
     } else {

input/input.h

@@ -86,6 +86,7 @@ typedef struct mp_cmd {
     double scale;               // for scaling numeric arguments
     const struct mp_cmd_def *def;
     char *sender; // name of the client API user which sent this
+    char *key_name; // string representation of the key binding
 } mp_cmd_t;
 
 struct mp_input_src {

player/command.c

@@ -4908,8 +4908,8 @@ int run_command(struct MPContext *mpctx, struct mp_cmd *cmd, struct mpv_node *re
         char state[3] = {'p', cmd->is_mouse_button ? 'm' : '-'};
         if (cmd->is_up_down)
             state[0] = cmd->repeated ? 'r' : (cmd->is_up ? 'u' : 'd');
-        event.num_args = 3;
-        event.args = (const char*[3]){"key-binding", name, state};
+        event.num_args = 4;
+        event.args = (const char*[4]){"key-binding", name, state, cmd->key_name};
         if (mp_client_send_event_dup(mpctx, target,
                                      MPV_EVENT_CLIENT_MESSAGE, &event) < 0)
         {