Add client_list var

README.asciidoc

@@ -813,8 +813,9 @@ Some of Kakoune state is available through environment variables:
  * `kak_opt_<name>`: value of option <name>
  * `kak_reg_<r>`: value of register <r>
  * `kak_session`: name of the current session
- * `kak_client`: name of current client
+ * `kak_client`: name of the current client
  * `kak_client_pid`: pid of the current client
+ * `kak_client_list`: list of clients connected to the current session
  * `kak_modified`: buffer has modifications not saved
  * `kak_source`: path of the file currently getting executed (through the source command)
  * `kak_cursor_line`: line of the end of the main selection

doc/manpages/expansions.asciidoc

@@ -88,9 +88,11 @@ informations about Kakoune's state:
 *kak_session*::
 	name of the current session
 *kak_client*::
-	name of current client
+	name of the current client
 *kak_client_pid*::
-	process id of current client
+	process id of the current client
+*kak_client_list*::
+	list of clients connected to the current session
 *kak_source*::
 	path of the file currently getting executed (through the source
 	command)

src/main.cc

@@ -135,6 +135,12 @@ void register_env_vars()
             "client_pid", false,
             [](StringView name, const Context& context) -> String
             { return to_string(context.client().pid()); }
+        }, {
+            "client_list", false,
+            [](StringView name, const Context& context) -> String
+            { return join(ClientManager::instance() |
+                          transform([](const std::unique_ptr<Client>& c) -> const String&
+                                   { return c->context().name(); }), ':'); }
         }, {
             "modified", false,
             [](StringView name, const Context& context) -> String