api/ui: externalize tabline

- Work with a bool[] array parallel to the UIWidget enum.
- Rename some functions.
- Documentation.

src/nvim/ui.c

@@ -47,6 +47,7 @@
 #define MAX_UI_COUNT 16
 
 static UI *uis[MAX_UI_COUNT];
+static bool ui_ext[UI_WIDGETS] = { 0 };
 static size_t ui_count = 0;
 static int row = 0, col = 0;
 static struct {
@@ -58,10 +59,6 @@ static int busy = 0;
 static int height, width;
 static int old_mode_idx = -1;
 
-static bool tabline_external = false;
-static bool cmdline_external = false;
-static bool wildmenu_external = false;
-
 // UI_CALL invokes a function on all registered UI instances. The functions can
 // have 0-5 arguments (configurable by SELECT_NTH).
 //
@@ -170,21 +167,25 @@ void ui_refresh(void)
   }
 
   int width = INT_MAX, height = INT_MAX;
-  bool pum_external = true;
-  bool tabline_external = true;
+  bool ext_widgets[UI_WIDGETS];
+  for (UIWidget i = 0; (int)i < UI_WIDGETS; i++) {
+    ext_widgets[i] = true;
+  }
 
   for (size_t i = 0; i < ui_count; i++) {
     UI *ui = uis[i];
     width = MIN(ui->width, width);
     height = MIN(ui->height, height);
-    pum_external &= ui->pum_external;
-    tabline_external &= ui->tabline_external;
+    for (UIWidget i = 0; (int)i < UI_WIDGETS; i++) {
+      ext_widgets[i] &= ui->ui_ext[i];
+    }
   }
 
   row = col = 0;
   screen_resize(width, height);
-  pum_set_external(pum_external);
-  ui_set_widget_external(kUITabline, tabline_external);
+  for (UIWidget i = 0; (int)i < UI_WIDGETS; i++) {
+    ui_set_external(i, ext_widgets[i]);
+  }
   ui_mode_info_set();
   old_mode_idx = -1;
   ui_cursor_shape();
@@ -564,30 +565,16 @@ void ui_cursor_shape(void)
   conceal_check_cursur_line();
 }
 
-bool ui_is_widget_external(UIWidget widget)
+/// Returns true if `widget` is externalized.
+bool ui_is_external(UIWidget widget)
 {
-  switch (widget) {
-    case kUITabline:
-      return tabline_external;
-    case kUICmdline:
-      return cmdline_external;
-    case kUIWildmenu:
-      return wildmenu_external;
-  }
-  return false;
+  return ui_ext[widget];
 }
 
-void ui_set_widget_external(UIWidget widget, bool external)
+/// Sets `widget` as "external".
+/// Such widgets are not drawn by Nvim; external UIs are expected to handle
+/// higher-level UI events and present the data.
+void ui_set_external(UIWidget widget, bool external)
 {
-  switch (widget) {
-    case kUITabline:
-      tabline_external = external;
-      break;
-    case kUICmdline:
-      cmdline_external = external;
-      break;
-    case kUIWildmenu:
-      wildmenu_external = external;
-      break;
-  }
+  ui_ext[widget] = external;
 }