Update single fetch headers approach to use response stub API

.changeset/response-stub.md

@@ -0,0 +1,25 @@
+---
+"@remix-run/server-runtime": patch
+---
+
+Add `ResponseStub` header interface for single fetch and deprecate the `headers` export
+
+- The `headers` export is no longer used when single fetch is enabled
+- `loader`/`action` functions now receive a mutable `response` parameter
+  - `type ResponseStub = { status: numbers | undefined, headers: Headers }`
+- To alter the status of a response, set the `status` field directly
+  - `response.status = 201`
+- To set headers on the Response, you may use:
+  - `response.headers.set`
+  - `response.headers.append`
+  - `response.headers.delete`
+- Each `loader`/`action`receives it's own unique `response` instance so you cannot see what other `loader`/`action` functions have set (which would be subject to race conditions)
+- If all status codes are unset or have values <200, the deepest status code will be used for the HTTP response
+- If any status codes are set to a value >=300, the highest >=300 value will be used for the HTTP Response
+- Remix tracks header operations and will replay them in order (action if present, then loaders top-down) after all handlers have completed on a fresh `Headers` instance that will be applied to the HTTP Response
+  - `headers.set` on any child handler will overwrite values from parent handlers
+  - `headers.append` can be used to set the same header from both a parent and child handler
+  - `headers.delete` can be used to delete a value set by a parent handler, but not a value set from a child handler
+- Because single fetch supports naked object returns, and you no longer need to return a `Response` instance to set status/headers, the `json`/`redirect`/`redirectDocument`/`defer` utilities are considered deprecated when using Single Fetch
+- You may still continue returning normal `Response` instances and they'll apply status codes in the same way, and will apply all headers via `headers.set` - overwriting any same-named header values from parents
+  - If you need to append, you will need to switch from returning a `Response` instance to using the new `response` parameter

integration/error-boundary-test.ts

@@ -2229,9 +2229,19 @@ test.describe("single fetch", () => {
         expect(await app.getHtml("#parent-error")).toEqual(
           '<p id="parent-error">Broken!</p>'
         );
-        expect(await app.getHtml("#parent-matches-data")).toEqual(
-          '<p id="parent-matches-data"></p>'
-        );
+        if (javaScriptEnabled) {
+          // This data remains in single fetch with JS because we don't revalidate
+          // due to the 500 action response
+          expect(await app.getHtml("#parent-matches-data")).toEqual(
+            '<p id="parent-matches-data">PARENT</p>'
+          );
+        } else {
+          // But without JS document requests call all loaders up to the
+          // boundary route so parent's data clears out
+          expect(await app.getHtml("#parent-matches-data")).toEqual(
+            '<p id="parent-matches-data"></p>'
+          );
+        }
         expect(await app.getHtml("#parent-data")).toEqual(
           '<p id="parent-data"></p>'
         );

integration/package.json

@@ -14,7 +14,7 @@
     "@remix-run/dev": "workspace:*",
     "@remix-run/express": "workspace:*",
     "@remix-run/node": "workspace:*",
-    "@remix-run/router": "0.0.0-experimental-c7dd3d3a",
+    "@remix-run/router": "0.0.0-experimental-0f302655",
     "@remix-run/server-runtime": "workspace:*",
     "@types/express": "^4.17.9",
     "@vanilla-extract/css": "^1.10.0",

integration/revalidate-test.ts

@@ -326,9 +326,9 @@ test.describe("single fetch", () => {
                           <li><Link to="/">/</Link></li>
                           <li><Link to="/parent">/parent</Link></li>
                           <li><Link to="/parent/child">/parent/child</Link></li>
-                          <li><Link to="/parent/child?revalidate=parent">/parent/child</Link></li>
-                          <li><Link to="/parent/child?revalidate=child">/parent/child</Link></li>
-                          <li><Link to="/parent/child?revalidate=parent,child">/parent/child</Link></li>
+                          <li><Link to="/parent/child?revalidate=parent">/parent/child?revalidate=parent</Link></li>
+                          <li><Link to="/parent/child?revalidate=child">/parent/child?revalidate=child</Link></li>
+                          <li><Link to="/parent/child?revalidate=parent,child">/parent/child?revalidate=parent,child</Link></li>
                         </ul>
                       </nav>
                       <Outlet />