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, 18 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 13884e865d..2aa147770d 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -1461,24 +1461,6 @@ nvim_strwidth({text})                                        *nvim_strwidth()*
     Return: ~
         Number of cells
 
-nvim_subscribe({event})                                     *nvim_subscribe()*
-    Subscribes to event broadcasts.
-
-    Attributes: ~
-        |RPC| only
-
-    Parameters: ~
-      • {event}  Event type string
-
-nvim_unsubscribe({event})                                 *nvim_unsubscribe()*
-    Unsubscribes to event broadcasts.
-
-    Attributes: ~
-        |RPC| only
-
-    Parameters: ~
-      • {event}  Event type string
-
 nvim__complete_set({index}, {opts})                     *nvim__complete_set()*
     EXPERIMENTAL: this API may change in the future.