api: list information about all channels/jobs.

Fire autocmd when channel opens or its info changes.
Add a way for API clients can describe themselves.

src/nvim/msgpack_rpc/channel.c

@@ -61,6 +61,7 @@ void rpc_start(Channel *channel)
   rpc->unpacker = msgpack_unpacker_new(MSGPACK_UNPACKER_INIT_BUFFER_SIZE);
   rpc->subscribed_events = pmap_new(cstr_t)();
   rpc->next_request_id = 1;
+  rpc->info = (Dictionary)ARRAY_DICT_INIT;
   kv_init(rpc->call_stack);
 
   if (channel->streamtype != kChannelStreamInternal) {
@@ -553,6 +554,7 @@ void rpc_free(Channel *channel)
 
   pmap_free(cstr_t)(channel->rpc.subscribed_events);
   kv_destroy(channel->rpc.call_stack);
+  api_free_dictionary(channel->rpc.info);
 }
 
 static bool is_rpc_response(msgpack_object *obj)
@@ -642,6 +644,23 @@ static WBuffer *serialize_response(uint64_t channel_id,
   return rv;
 }
 
+void rpc_set_client_info(uint64_t id, Dictionary info)
+{
+  Channel *chan = find_rpc_channel(id);
+  if (!chan) {
+    abort();
+  }
+
+  api_free_dictionary(chan->rpc.info);
+  chan->rpc.info = info;
+  channel_info_changed(chan, false);
+}
+
+Dictionary rpc_client_info(Channel *chan)
+{
+  return copy_dictionary(chan->rpc.info);
+}
+
 #if MIN_LOG_LEVEL <= DEBUG_LOG_LEVEL
 #define REQ "[request]  "
 #define RES "[response] "

src/nvim/msgpack_rpc/channel_defs.h

@@ -31,6 +31,7 @@ typedef struct {
   msgpack_unpacker *unpacker;
   uint64_t next_request_id;
   kvec_t(ChannelCallFrame *) call_stack;
+  Dictionary info;
 } RpcState;
 
 #endif  // NVIM_MSGPACK_RPC_CHANNEL_DEFS_H