fix(tui): don't treat remote TUI as GUI (#36319)

Set "stdin_tty" and "stdout_tty" UI options, so that a remote TUI is not
treated as a GUI.

src/nvim/api/ui.c

@@ -169,6 +169,7 @@ void nvim_ui_attach(uint64_t channel_id, Integer width, Integer height, Dict opt
     return;
   }
   RemoteUI *ui = xcalloc(1, sizeof(RemoteUI));
+  ui->channel_id = channel_id;
   ui->width = (int)width;
   ui->height = (int)height;
   ui->pum_row = -1.0;
@@ -195,7 +196,6 @@ void nvim_ui_attach(uint64_t channel_id, Integer width, Integer height, Dict opt
     ui->ui_ext[kUICmdline] = true;
   }
 
-  ui->channel_id = channel_id;
   ui->cur_event = NULL;
   ui->hl_id = 0;
   ui->client_col = -1;
@@ -427,7 +427,9 @@ static void ui_set_option(RemoteUI *ui, bool init, String name, Object value, Er
     VALIDATE_T("stdin_tty", kObjectTypeBoolean, value.type, {
       return;
     });
+    if (ui->channel_id == CHAN_STDIO) {
       stdin_isatty = value.data.boolean;
+    }
     ui->stdin_tty = value.data.boolean;
     return;
   }
@@ -436,7 +438,9 @@ static void ui_set_option(RemoteUI *ui, bool init, String name, Object value, Er
     VALIDATE_T("stdout_tty", kObjectTypeBoolean, value.type, {
       return;
     });
+    if (ui->channel_id == CHAN_STDIO) {
       stdout_isatty = value.data.boolean;
+    }
     ui->stdout_tty = value.data.boolean;
     return;
   }

src/nvim/ui_client.c

@@ -105,14 +105,12 @@ void ui_client_attach(int width, int height, char *term, bool rgb)
     PUT_C(opts, "term_name", CSTR_AS_OBJ(term));
   }
   PUT_C(opts, "term_colors", INTEGER_OBJ(t_colors));
-  if (!ui_client_is_remote) {
   PUT_C(opts, "stdin_tty", BOOLEAN_OBJ(stdin_isatty));
   PUT_C(opts, "stdout_tty", BOOLEAN_OBJ(stdout_isatty));
   if (ui_client_forward_stdin) {
     PUT_C(opts, "stdin_fd", INTEGER_OBJ(UI_CLIENT_STDIN_FD));
     ui_client_forward_stdin = false;  // stdin shouldn't be forwarded again #22292
   }
-  }
   ADD_C(args, DICT_OBJ(opts));
 
   rpc_send_event(ui_client_channel_id, "nvim_ui_attach", args);

test/functional/terminal/tui_spec.lua

@@ -2562,6 +2562,13 @@ describe('TUI', function()
       eq(true, child_exec_lua('return _G.result'))
     end)
   end)
+
+  it('nvim_ui_send works', function()
+    child_session:request('nvim_ui_send', '\027]2;TEST_TITLE\027\\')
+    retry(nil, nil, function()
+      eq('TEST_TITLE', api.nvim_buf_get_var(0, 'term_title'))
+    end)
+  end)
 end)
 
 describe('TUI', function()
@@ -3887,9 +3894,8 @@ describe('TUI client', function()
   it('connects to remote instance (with its own TUI)', function()
     local _, screen_server, screen_client = start_tui_and_remote_client()
 
-    -- XXX: should has("gui_running") be 1 when there is a remote TUI?
     feed_data(':echo "GUI Running: " .. has("gui_running")\013')
-    screen_client:expect({ any = 'GUI Running: 1' })
+    screen_client:expect({ any = 'GUI Running: 0' })
 
     -- grid smaller than containing terminal window is cleared properly
     feed_data(":call setline(1,['a'->repeat(&columns)]->repeat(&lines))\n")
@@ -3984,9 +3990,8 @@ describe('TUI client', function()
     ]])
     feed_data('\027')
 
-    -- XXX: should has("gui_running") be 1 when there is a remote TUI?
     feed_data(':echo "GUI Running: " .. has("gui_running")\013')
-    screen_client:expect({ any = 'GUI Running: 1' })
+    screen_client:expect({ any = 'GUI Running: 0' })
 
     -- Run :restart on the client.
     -- The client should start a new server while the original server should exit.
@@ -4049,6 +4054,14 @@ describe('TUI client', function()
     end)
   end)
 
+  it('nvim_ui_send works with remote client #36317', function()
+    local server, _, _ = start_headless_server_and_client()
+    server:request('nvim_ui_send', '\027]2;TEST_TITLE\027\\')
+    retry(nil, nil, function()
+      eq('TEST_TITLE', api.nvim_buf_get_var(0, 'term_title'))
+    end)
+  end)
+
   it('throws error when no server exists', function()
     clear()
     local screen = tt.setup_child_nvim({