fix(server): serve the page for HEAD when the GET handler returns nothing

.changeset/head-page-fallthrough.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/start": patch
+---
+
+Serve the page for a `HEAD` request when a route file exports both a page and a `GET` that returns nothing, such as a `[...404].tsx`. The server threw "did not return a response" and answered 500 instead of rendering the page as it does for `GET`.

apps/tests/src/e2e/api-call.test.ts

@@ -22,6 +22,16 @@ test.describe("api calls", () => {
     expect(redirectResp.headers.get("x-shared-header")).toBe("event");
   });
 
+  test("should serve the page for HEAD when the GET handler returns nothing", async () => {
+    // `[...404].tsx` exports a page and a `GET` that only answers JSON requests.
+    const get = await fetch("http://localhost:3000/no-such-page");
+    const head = await fetch("http://localhost:3000/no-such-page", { method: "HEAD" });
+
+    expect(get.status).toBe(404);
+    expect(head.status).toBe(get.status);
+    expect(head.headers.get("content-type")).toBe(get.headers.get("content-type"));
+  });
+
   test("should preserve multiple Set-Cookie headers on redirect (RFC 6265)", async () => {
     const response = await fetch("http://localhost:3000/api/multi-set-cookie-redirect", {
       redirect: "manual",

packages/start/src/server/handler.ts

@@ -47,7 +47,9 @@ export function createBaseHandler(
           if (res !== undefined) {
             return res;
           }
-          if (event.request.method !== "GET") {
+          // A HEAD request runs the `GET` handler when there is no `HEAD` one,
+          // so it falls through to the page the same way a `GET` does.
+          if (event.request.method !== "GET" && event.request.method !== "HEAD") {
             throw new Error(
               `API handler for ${event.request.method} "${event.request.url}" did not return a response.`,
             );