fix(routing): notify about double routing roots

Having two routing roots on the page at once causes problems, as they are both listening to the same routing events

If they have the same routes supplied it's probably ok, just double broadcast messages.

But if they have different routes then one will broadcast a 404 event, and one will not.

Better not to do it at all. So that will now throw an error in dev and log an error message in prod to enable it to be caught

package.json

@@ -37,6 +37,7 @@
     "@testing-library/user-event": "^14.4.3",
     "@types/history": "^4.7.7",
     "@types/jest": "^28.1.4",
+    "@types/node": "^20.4.9",
     "@types/react": "^17.0.29",
     "@types/react-dom": "^18.0.6",
     "@types/testing-library__jest-dom": "^5.14.1",
@@ -72,9 +73,9 @@
   },
   "peerDependencies": {
     "@xstate/react": "^3.x",
+    "react": ">= 16.8.0 < 19.0.0",
     "xstate": ">= 4.20 < 5.0.0",
-    "zod": "^3.x",
-    "react": ">= 16.8.0 < 19.0.0"
+    "zod": "^3.x"
   },
   "scripts": {
     "lint": "eslint 'src/**/*'",

src/routing/Link.tsx

@@ -61,7 +61,7 @@ export function Link<TRoute extends AnyRoute>({
   // and everything that consumes params/query already checks for undefined
   const { params, query, meta, ...props } = rest;
 
-  let timeout: number | undefined;
+  let timeout: ReturnType<typeof setTimeout> | undefined;
   const href = useHref(to, params, query);
   const onMouseDown: React.MouseEventHandler<HTMLAnchorElement> | undefined =
     preloadOnInteraction

src/routing/index.ts

@@ -23,4 +23,8 @@ export {
 export { useIsRouteActive } from "./useIsRouteActive";
 export { useRouteArgsIfActive } from "./useRouteArgsIfActive";
 
-export { RoutingContext, TestRoutingContext } from "./providers";
+export {
+  RoutingContext,
+  TestRoutingContext,
+  useInRoutingContext,
+} from "./providers";

src/routing/providers.tsx

@@ -21,6 +21,15 @@ function useRoutingContext() {
   return context;
 }
 
+/**
+ * @private
+ */
+export function useInRoutingContext(): boolean {
+  const context = useContext(RoutingContext);
+
+  return context !== undefined;
+}
+
 export function useActiveRouteEvents() {
   try {
     const context = useRoutingContext();

src/xstateTree.spec.tsx

@@ -1,5 +1,6 @@
 import { render } from "@testing-library/react";
 import { assign } from "@xstate/immer";
+import { createMemoryHistory } from "history";
 import React from "react";
 import { createMachine, interpret } from "xstate";
 
@@ -262,4 +263,81 @@ describe("xstate-tree", () => {
       expect(view2).toBe(getMultiSlotViewForChildren(interpreter2, "ignored"));
     });
   });
+
+  describe("rendering a root inside of a root", () => {
+    it("throws an error during rendering if both are routing roots", async () => {
+      const machine = createMachine({
+        id: "test",
+        initial: "idle",
+        states: {
+          idle: {},
+        },
+      });
+
+      const RootMachine = createXStateTreeMachine(machine, {
+        View() {
+          return <p>I am root</p>;
+        },
+      });
+      const Root = buildRootComponent(RootMachine, {
+        basePath: "/",
+        history: createMemoryHistory(),
+        routes: [],
+      });
+
+      const Root2Machine = createXStateTreeMachine(machine, {
+        View() {
+          return <Root />;
+        },
+      });
+      const Root2 = buildRootComponent(Root2Machine, {
+        basePath: "/",
+        history: createMemoryHistory(),
+        routes: [],
+      });
+
+      try {
+        const { rerender } = render(<Root2 />);
+        rerender(<Root2 />);
+      } catch (e: any) {
+        expect(e.message).toMatchInlineSnapshot(
+          `"Routing root rendered inside routing context, this implies a bug"`
+        );
+        return;
+      }
+
+      throw new Error("Should have thrown");
+    });
+
+    it("does not throw an error if either or one are a routing root", async () => {
+      const machine = createMachine({
+        id: "test",
+        initial: "idle",
+        states: {
+          idle: {},
+        },
+      });
+
+      const RootMachine = createXStateTreeMachine(machine, {
+        View() {
+          return <p>I am root</p>;
+        },
+      });
+      const Root = buildRootComponent(RootMachine);
+
+      const Root2Machine = createXStateTreeMachine(machine, {
+        View() {
+          return <Root />;
+        },
+      });
+      const Root2 = buildRootComponent(Root2Machine, {
+        basePath: "/",
+        history: createMemoryHistory(),
+        routes: [],
+      });
+
+      const { rerender } = render(<Root2 />);
+      rerender(<Root2 />);
+    });
+  });
 });

src/xstateTree.tsx

@@ -23,6 +23,7 @@ import {
   RoutingContext,
   RoutingEvent,
   SharedMeta,
+  useInRoutingContext,
 } from "./routing";
 import { useActiveRouteEvents } from "./routing/providers";
 import { GetSlotNames, Slot } from "./slots";
@@ -353,6 +354,16 @@ export function buildRootComponent(
     const setActiveRouteEvents = (events: RoutingEvent<any>[]) => {
       activeRouteEventsRef.current = events;
     };
+    const insideRoutingContext = useInRoutingContext();
+    if (insideRoutingContext && typeof routing !== "undefined") {
+      const m =
+        "Routing root rendered inside routing context, this implies a bug";
+      if (process.env.NODE_ENV !== "production") {
+        throw new Error(m);
+      }
+
+      console.error(m);
+    }
 
     useEffect(() => {
       function handler(event: GlobalEvents) {

tsconfig.json

@@ -19,7 +19,7 @@
     "moduleResolution": "node",
     "esModuleInterop": true,
     "declarationMap": true,
-    "types": ["jest"],
+    "types": ["jest", "node"],
     "paths": {
       "@koordinates/xstate-tree": ["./src/index.ts"]
     },