feat(:restart): reattach all UIs (#38683)

This is quite easy since [command] is now only executed once on UIEnter.

runtime/doc/gui.txt

@@ -74,9 +74,8 @@ Restart Nvim
                 1. Stops Nvim using `:qall` (or |+cmd|, if given).
                 2. Starts a new Nvim server using the same |v:argv| (except
                    `-- [file…]` files).
-                3. Attaches the current UI to the new Nvim server and runs
-                   `[command]` on it. Other UIs (if any) will not reattach
-                   on restart (this may change in the future).
+                3. Attaches all UIs to the new Nvim server and runs `[command]`
+                   on it.
 
                 Example: discard changes and stop with `:qall!`, then restart: >
                     :restart +qall!
@@ -86,7 +85,7 @@ Restart Nvim
                     :restart lua vim.pack.update()
 <
                 Note: Only works if the UI and server are on the same system.
-                Note: If the UI hasn't implemented the "restart" UI event,
+                Note: If no attached UI implements the "restart" UI event,
                 this command will lead to a dangling server process.
 
 ------------------------------------------------------------------------------

runtime/doc/news.txt

@@ -404,7 +404,7 @@ UI
   • Highlights the cmdline as you type.
   • Provides the |pager| as a buffer + window.
   • Currently experimental. To enable it: `require('vim._core.ui2').enable()`
-• |:restart| restarts Nvim and reattaches the current UI.
+• |:restart| restarts Nvim and reattaches all UIs.
 • |:connect| dynamically connects the current UI to the server at the given
   address.
 • |:checkhealth| shows a summary in the header for every healthcheck.

src/nvim/api/ui.c

@@ -253,24 +253,6 @@ void nvim_ui_detach(uint64_t channel_id, Error *err)
   remote_ui_disconnect(channel_id, err, false);
 }
 
-/// Sends a "restart" UI event to the UI on the given channel.
-///
-/// @return  false if there is no UI on the channel, otherwise true
-bool remote_ui_restart(uint64_t channel_id, const char *listen_addr, Error *err)
-{
-  RemoteUI *ui = get_ui_or_err(channel_id, err);
-  if (!ui) {
-    return false;
-  }
-
-  MAXSIZE_TEMP_ARRAY(args, 1);
-  ADD_C(args, CSTR_AS_OBJ(listen_addr));
-
-  push_call(ui, "restart", args);
-  ui_flush_buf(ui, false);
-  return true;
-}
-
 // Send a connect UI event to the UI on the given channel
 void remote_ui_connect(uint64_t channel_id, char *server_addr, Error *err)
 {

src/nvim/api/ui_events.in.h

@@ -30,7 +30,7 @@ void flush(void)
 void connect(String server_addr)
   FUNC_API_SINCE(14) FUNC_API_REMOTE_ONLY FUNC_API_REMOTE_IMPL FUNC_API_CLIENT_IMPL;
 void restart(String listen_addr)
-  FUNC_API_SINCE(14) FUNC_API_REMOTE_ONLY FUNC_API_REMOTE_IMPL FUNC_API_CLIENT_IMPL;
+  FUNC_API_SINCE(14) FUNC_API_REMOTE_ONLY FUNC_API_CLIENT_IMPL;
 void suspend(void)
   FUNC_API_SINCE(3);
 void set_title(String title)

src/nvim/ex_docmd.c

@@ -5081,15 +5081,9 @@ static void ex_restart(exarg_T *eap)
   arena_mem_free(result_mem);
   result_mem = NULL;
 
-  // Send restart event with new listen address to current UI.
-  if (!no_ui && !remote_ui_restart(current_ui, listen_addr, &err)) {
-    if (ERROR_SET(&err)) {
-      ELOG("%s", err.msg);  // UI disappeared already?
-      api_clear_error(&err);
-    }
-    xfree(listen_addr);
-    goto fail_2;
-  }
+  // Send restart event with new listen address to all UIs.
+  ui_call_restart(cstr_as_string(listen_addr));
+  ui_flush();
   xfree(listen_addr);
 
   char *quit_cmd = (eap->do_ecmd_cmd) ? eap->do_ecmd_cmd : "qall";

test/functional/terminal/tui_spec.lua

@@ -4263,22 +4263,36 @@ describe('TUI client', function()
   it(':restart works when connecting to remote instance (with its own TUI)', function()
     local _, screen_server, screen_client = start_tui_and_remote_client()
 
-    -- The remote client should attach to the new server.
+    -- Both clients should attach to the new server.
     feed_data(':restart +qall!\n')
-    screen_client:expect([[
+    local screen_restarted = [[
       ^                                                  |
       {100:~                                                 }|*3
       {3:[No Name]                                         }|
                                                         |
       {5:-- TERMINAL --}                                    |
-    ]])
-    screen_server:expect({ any = vim.pesc('[Process exited 0]') })
+    ]]
+    screen_client:expect(screen_restarted)
+    screen_server:expect(screen_restarted)
 
     feed_data(':echo "GUI Running: " .. has("gui_running")\013')
     screen_client:expect({ any = 'GUI Running: 0' })
 
-    feed_data(':q!\r')
+    -- The :vsplit command should only be executed once.
+    feed_data(':restart vsplit\r')
+    screen_restarted = [[
+      ^                         │                        |
+      {100:~                        }│{100:~                       }|*3
+      {3:[No Name]                 }{2:[No Name]               }|
+                                                        |
+      {5:-- TERMINAL --}                                    |
+    ]]
+    screen_client:expect(screen_restarted)
+    screen_server:expect(screen_restarted)
+
+    feed_data(':qall!\r')
     screen_client:expect({ any = vim.pesc('[Process exited 0]') })
+    screen_server:expect({ any = vim.pesc('[Process exited 0]') })
   end)
 
   local function start_headless_server_and_client(use_testlog)