Throw an ErrorResponse instead of just an Error for route with no action

.changeset/wicked-avocados-fly.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/react": patch
+---
+
+Throw a semantically correct 405 `ErrorResponse` instead of just an `Error` when submitting to a route without an `action`

integration/action-test.ts

@@ -95,6 +95,18 @@ test.describe("actions", () => {
             return <div id="${REDIRECT_TARGET}">${PAGE_TEXT}</div>
           }
         `,
+
+        "app/routes/no-action.tsx": js`
+          import { Form } from "@remix-run/react";
+
+          export default function Component() {
+            return (
+              <Form method="post">
+                <button type="submit">Submit without action</button>
+              </Form>
+            );
+          }
+        `,
       },
     });
 
@@ -145,6 +157,22 @@ test.describe("actions", () => {
     await page.waitForSelector(`#text:has-text("${SUBMITTED_VALUE}")`);
   });
 
+  test("throws a 405 when no action exists", async ({ page }) => {
+    let app = new PlaywrightFixture(appFixture, page);
+    await app.goto(`/no-action`);
+    await page.click("button[type=submit]");
+    await page.waitForSelector(`h1:has-text("405 Method Not Allowed")`);
+    expect(logs.length).toBe(2);
+    expect(logs[0]).toMatch('Route "routes/no-action" does not have an action');
+    // logs[1] is the raw ErrorResponse instance from the boundary but playwright
+    // seems to just log the name of the constructor, which in the minified code
+    // is meaningless so we don't bother asserting
+
+    // The rest of the tests in this suite assert no logs, so clear this out to
+    // avoid failures in afterEach
+    logs = [];
+  });
+
   test("properly encodes form data for request.text() usage", async ({
     page,
   }) => {

integration/resource-routes-test.ts

@@ -247,7 +247,7 @@ test.describe("loader in an app", async () => {
     await app.goto("/");
     await app.clickSubmitButton("/no-action");
     let html = await app.getHtml();
-    expect(html).toMatch("Application Error");
+    expect(html).toMatch("405 Method Not Allowed");
     expect(logs[0]).toContain(
       'Route "routes/no-action" does not have an action'
     );

packages/remix-react/routes.tsx

@@ -1,4 +1,5 @@
 import * as React from "react";
+import { UNSAFE_ErrorResponseImpl as ErrorResponse } from "@remix-run/router";
 import type {
   DataRouteObject,
   ShouldRevalidateFunction,
@@ -140,7 +141,9 @@ export function createClientRoutes(
             `Route "${route.id}" does not have an action, but you are trying ` +
             `to submit to it. To fix this, please add an \`action\` function to the route`;
           console.error(msg);
-          return Promise.reject(new Error(msg));
+          return Promise.reject(
+            new ErrorResponse(405, "Method Not Allowed", new Error(msg), true)
+          );
         }
 
         return fetchServerHandler(request, route);