perf(claims): trust server link state at hydration

.changeset/hydration-trusts-server-link-state.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/router": patch
+---
+
+Link claims trust the server's link state at hydration: an anchor the server marked is registered without resolving its URL, and is resolved on the first routing change. Anchors with an authored `aria-current`, and pages rendered without server link state, are resolved at claim as before.

src/claims.ts

@@ -155,10 +155,10 @@ export function setupLinkClaims(
       if (existing) return refresh(a, existing);
       // server HTML (hydrating, or already in the document) pairs the router's
       // `aria-current` with `data-active` and never writes over an authored one
+      const hydrating = serverState && isHydrating();
       const rec = {
         owned:
-          serverState &&
-          (isHydrating() || a.isConnected) &&
+          (hydrating || (serverState && a.isConnected)) &&
           a.getAttribute("aria-current") === "page" &&
           a.hasAttribute("data-active")
       };
@@ -170,7 +170,11 @@ export function setupLinkClaims(
         registry.add(a);
         onCleanup(() => registry.delete(a));
       }
-      refresh(a, rec);
+      // A hydrating anchor already carries the server's state for the location
+      // hydrating now, unless the server skipped it for an authored
+      // `aria-current`. Skipping the refresh keeps URL resolution off the load
+      // path; the sweep resolves it on the first routing change.
+      if (!hydrating || (!rec.owned && a.getAttribute("aria-current") !== null)) refresh(a, rec);
     })
   );
 }

test/server/hydration-link-state.spec.ts

@@ -142,7 +142,20 @@ describe("link state across hydration", () => {
     for (const [text, value] of Object.entries(expected))
       expect([text, state(anchor(document, text))]).toEqual([text, value]);
 
+    // anchors resolve against the document; record which ones hydration parses
+    const resolved: string[] = [];
+    const NativeURL = window.URL;
+    window.URL = new Proxy(NativeURL, {
+      construct(target, args) {
+        if (args[1] === document.baseURI) resolved.push(args[0]);
+        return new target(...args);
+      }
+    });
     window.eval(code);
+    window.URL = NativeURL;
+    // the server's state is trusted: only the anchor it skipped for an
+    // authored aria-current is resolved at hydration
+    expect(resolved).toEqual(["/about"]);
     const app = window.hydrationTest;
     // the boundary's anchor streams in after hydration starts
     stream.release();