fix(studio): swap the tab icon in the same frame as the tab

packages/studio/src/components/dock/DockTab.tsx

@@ -31,40 +31,38 @@ const TAB_ICONS: Record<PanelId, Icon> = {
   slideshow: Presentation,
 };
 
-/** A dock tab. Only the shown tab carries its type icon and close glyph; the rest are labels. */
+/**
+ * A dock tab. dock.css shows the type icon and close glyph on the shown tab only, keyed on
+ * dockview's own tab class, so they swap in the frame the tab changes rather than a render later.
+ */
 export function DockTab({ api }: IDockviewPanelHeaderProps) {
   const subscribe = useCallback(
     (onChange: () => void) => {
-      const subscriptions = [api.onDidTitleChange(onChange), api.onDidVisibilityChange(onChange)];
-      return () => {
-        for (const subscription of subscriptions) subscription.dispose();
-      };
+      const subscription = api.onDidTitleChange(onChange);
+      return () => subscription.dispose();
     },
     [api],
   );
   const title = useSyncExternalStore(subscribe, () => api.title ?? "");
-  const shown = useSyncExternalStore(subscribe, () => api.isVisible);
-  const TypeIcon = shown && isPanelId(api.id) ? TAB_ICONS[api.id] : null;
+  const TypeIcon = isPanelId(api.id) ? TAB_ICONS[api.id] : null;
   return (
     <div className="hf-dock-tab">
       {TypeIcon ? <TypeIcon className="hf-dock-tab-icon" size={14} aria-hidden /> : null}
       <span className="hf-dock-tab-label">{title}</span>
-      {shown ? (
-        // Same shape as dockview's own close control: a tab cannot hold a focusable button.
-        <div
-          role="button"
-          tabIndex={-1}
-          aria-label={`Close ${title}`}
-          className="hf-dock-tab-close"
-          onPointerDown={(event) => event.stopPropagation()}
-          onClick={(event) => {
-            event.stopPropagation();
-            api.close();
-          }}
-        >
-          <X size={12} aria-hidden />
-        </div>
-      ) : null}
+      {/* Same shape as dockview's own close control: a tab cannot hold a focusable button. */}
+      <div
+        role="button"
+        tabIndex={-1}
+        aria-label={`Close ${title}`}
+        className="hf-dock-tab-close"
+        onPointerDown={(event) => event.stopPropagation()}
+        onClick={(event) => {
+          event.stopPropagation();
+          api.close();
+        }}
+      >
+        <X size={12} aria-hidden />
+      </div>
     </div>
   );
 }

packages/studio/src/components/dock/DockTabs.test.tsx

@@ -1,5 +1,7 @@
 // @vitest-environment happy-dom
 
+import { readFileSync } from "node:fs";
+import path from "node:path";
 import { act } from "react";
 import { createRoot, type Root } from "react-dom/client";
 import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
@@ -40,6 +42,13 @@ const original = {
   offsetWidth: Object.getOwnPropertyDescriptor(HTMLElement.prototype, "offsetWidth"),
 };
 beforeAll(() => {
+  // The shown-tab-only rule lives in dock.css; apply it so computed display is what a user sees.
+  const style = document.createElement("style");
+  style.textContent = readFileSync(path.join(import.meta.dirname, "dock.css"), "utf8").replace(
+    /@import[^;]*;/,
+    "",
+  );
+  document.head.append(style);
   Object.defineProperties(HTMLElement.prototype, {
     offsetLeft: { ...layout.offsetLeft, configurable: true },
     offsetWidth: { ...layout.offsetWidth, configurable: true },
@@ -83,6 +92,10 @@ afterEach(() => {
 const tab = (id: PanelId) => host.querySelector<HTMLElement>(`[data-tab-panel-id="${id}"]`);
 const stripOf = (id: PanelId) => tab(id)?.closest<HTMLElement>(".dv-tabs-container");
 const groupOf = (id: PanelId) => tab(id)?.closest<HTMLElement>(".dv-groupview");
+const shows = (id: PanelId, part: "icon" | "close") => {
+  const element = tab(id)?.querySelector(`.hf-dock-tab-${part}`);
+  return element ? getComputedStyle(element).display !== "none" : false;
+};
 
 async function activate(id: PanelId) {
   // dockview settles the active panel on a microtask; `act(async)` waits for it.
@@ -92,21 +105,20 @@ async function activate(id: PanelId) {
 describe("dock tabs", () => {
   it("draw the type icon and close glyph on the shown tab only", () => {
     for (const id of ["design", "compositions"] as const) {
-      expect(tab(id)?.querySelector(".hf-dock-tab-icon")).not.toBeNull();
-      expect(tab(id)?.querySelector(".hf-dock-tab-close")).not.toBeNull();
+      expect(shows(id, "icon")).toBe(true);
+      expect(shows(id, "close")).toBe(true);
     }
     for (const id of ["layers", "renders", "variables", "assets", "code", "catalog"] as const) {
-      expect(tab(id)?.querySelector(".hf-dock-tab-icon")).toBeNull();
-      expect(tab(id)?.querySelector(".hf-dock-tab-close")).toBeNull();
-      expect(tab(id)?.textContent).toBe(tab(id)?.getAttribute("aria-label"));
+      expect(shows(id, "icon")).toBe(false);
+      expect(shows(id, "close")).toBe(false);
     }
   });
 
   it("move the icon to the newly shown tab and drop it from the old one", async () => {
     await activate("layers");
-    expect(tab("layers")?.querySelector(".hf-dock-tab-icon")).not.toBeNull();
-    expect(tab("design")?.querySelector(".hf-dock-tab-icon")).toBeNull();
-    expect(tab("design")?.querySelector(".hf-dock-tab-close")).toBeNull();
+    expect(shows("layers", "icon")).toBe(true);
+    expect(shows("design", "icon")).toBe(false);
+    expect(shows("design", "close")).toBe(false);
   });
 
   it("name the close control after the panel, and close only that panel", async () => {

packages/studio/src/components/dock/dock.css

@@ -136,6 +136,11 @@
   gap: 6px;
 }
 
+.hf-dock .dv-inactive-tab .hf-dock-tab-icon,
+.hf-dock .dv-inactive-tab .hf-dock-tab-close {
+  display: none;
+}
+
 .hf-dock-tab-icon {
   flex: none;
   animation: hf-dock-tab-icon-in 80ms ease-out;

packages/studio/src/components/dock/dockTabFill.ts

@@ -44,7 +44,7 @@ function markClippedEdges(list: HTMLElement) {
  */
 export function installTabFill(api: DockviewApi, root: HTMLElement): () => void {
   const lists = () => root.querySelectorAll<HTMLElement>(".dv-tabs-container");
-  // Tab widths change when a tab gains or loses its icon, after React renders it.
+  // Tab widths also change with no dockview event: a renamed title, a late web font.
   const resizeObserver = new ResizeObserver(() => placeAll());
   const observed = new Set<Element>();
   function observe(elements: Iterable<Element>) {