fix: don't throw when history.state is null after replaceState

.changeset/null-history-state-depth.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/router": patch
+---
+
+Don't throw on import when `history.state` is still null after `replaceState` (seen in iOS WKWebView embeds)

src/lifecycle.ts

@@ -50,7 +50,7 @@ export function saveCurrentDepth() {
   if (!window.history.state || window.history.state._depth == null) {
     window.history.replaceState({ ...window.history.state, _depth: window.history.length - 1 }, "");
   }
-  depth = window.history.state._depth;
+  depth = window.history.state?._depth ?? window.history.length - 1;
 }
 if (!isServer) {
   saveCurrentDepth();

test/lifecycle.spec.ts

@@ -1,5 +1,5 @@
 import { vi } from "vitest";
-import { createBeforeLeave } from "../src/lifecycle.js";
+import { createBeforeLeave, saveCurrentDepth } from "../src/lifecycle.js";
 import type { BeforeLeaveEventArgs, Location } from "../src/types.js";
 
 const mockLocation = { pathname: "/", search: "", hash: "", query: {}, state: null, key: "" } as unknown as Location;
@@ -49,3 +49,14 @@ describe("createBeforeLeave", () => {
     expect(listener).not.toHaveBeenCalled();
   });
 });
+
+describe("saveCurrentDepth", () => {
+  afterEach(() => vi.restoreAllMocks());
+
+  test("does not throw when replaceState leaves history.state null", () => {
+    vi.spyOn(window.history, "state", "get").mockReturnValue(null);
+    vi.spyOn(window.history, "replaceState").mockImplementation(() => {});
+
+    expect(() => saveCurrentDepth()).not.toThrow();
+  });
+});