feat(api): broadcast events to ALL channels #28487

Problem:
`vim.rpcnotify(0)` and `rpcnotify(0)` are documented as follows:

    If {channel} is 0, the event is broadcast to all channels.

But that's not actually true. Channels must call `nvim_subscribe` to
receive "broadcast" events, so it's actually "multicast".

- Assuming there is a use-case for "broadcast", the current model adds
  an extra step for broadcasting: all channels need to "subscribe".
- The presence of `nvim_subscribe` is a source of confusion for users,
  because its name implies something more generally useful than what it
  does.

Presumably the use-case of `nvim_subscribe` is to avoid "noise" on RPC
channels not expected a broadcast notification, and potentially an error
if the channel client reports an unknown event.

Solution:
- Deprecate `nvim_subscribe`/`nvim_unsubscribe`.
  - If applications want to multicast, they can keep their own multicast
    list. Or they can use `nvim_list_chans()` and `nvim_get_chan_info()`
    to enumerate and filter the clients they want to target.
- Always send "broadcast" events to ALL channels. Don't require channels
  to "subscribe" to receive broadcasts. This matches the documented
  behavior of `rpcnotify()`.

1 files changed, 0 insertions, 30 deletions

diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index f5b7c8abdd..fc780e1248 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -1334,36 +1334,6 @@ void nvim_put(ArrayOf(String) lines, String type, Boolean after, Boolean follow,
   });
 }
 
-/// Subscribes to event broadcasts.
-///
-/// @param channel_id Channel id (passed automatically by the dispatcher)
-/// @param event      Event type string
-void nvim_subscribe(uint64_t channel_id, String event)
-  FUNC_API_SINCE(1) FUNC_API_REMOTE_ONLY
-{
-  size_t length = (event.size < METHOD_MAXLEN ? event.size : METHOD_MAXLEN);
-  char e[METHOD_MAXLEN + 1];
-  memcpy(e, event.data, length);
-  e[length] = NUL;
-  rpc_subscribe(channel_id, e);
-}
-
-/// Unsubscribes to event broadcasts.
-///
-/// @param channel_id Channel id (passed automatically by the dispatcher)
-/// @param event      Event type string
-void nvim_unsubscribe(uint64_t channel_id, String event)
-  FUNC_API_SINCE(1) FUNC_API_REMOTE_ONLY
-{
-  size_t length = (event.size < METHOD_MAXLEN
-                   ? event.size
-                   : METHOD_MAXLEN);
-  char e[METHOD_MAXLEN + 1];
-  memcpy(e, event.data, length);
-  e[length] = NUL;
-  rpc_unsubscribe(channel_id, e);
-}
-
 /// Returns the 24-bit RGB value of a |nvim_get_color_map()| color name or
 /// "#rrggbb" hexadecimal string.
 ///