fix(fetch): default Request priority on the inner request

Move the "auto" default from the RequestInit WebIDL converter to
makeRequest so an omitted init stays empty after conversion. Restores
the Object.keys empty-init check.

Assisted by Cursor
Signed-off-by: Yagiz Nizipli <yagiz@nizipli.com>

Author: anonrig

lib/web/fetch/request.js

@@ -30,39 +30,6 @@ const { getMaxListeners, setMaxListeners, defaultMaxListeners } = require('node:
 
 const kAbortController = Symbol('abortController')
 
-/**
- * Fetch's "If init is not empty" check is based on user-specified
- * RequestInit members, not dictionary defaults. undici's `priority`
- * member defaults to `"auto"`, so `Object.keys(convertedInit)` is
- * never empty and would otherwise force the expensive header
- * clone/clear/re-append path on every `fetch(url)` / `new Request(url)`.
- *
- * Matches the spec / Servo / Chromium "any members present" test.
- *
- * @param {object | null | undefined} init
- * @returns {boolean}
- */
-function requestInitHasUserMembers (init) {
-  return init != null && (
-    init.method !== undefined ||
-    init.headers !== undefined ||
-    init.body !== undefined ||
-    init.referrer !== undefined ||
-    init.referrerPolicy !== undefined ||
-    init.mode !== undefined ||
-    init.credentials !== undefined ||
-    init.cache !== undefined ||
-    init.redirect !== undefined ||
-    init.integrity !== undefined ||
-    init.keepalive !== undefined ||
-    init.signal !== undefined ||
-    'window' in init ||
-    init.duplex !== undefined ||
-    init.dispatcher !== undefined ||
-    init.priority !== undefined
-  )
-}
-
 const requestFinalizer = new FinalizationRegistry(({ signal, abort }) => {
   signal.removeEventListener('abort', abort)
 })
@@ -149,8 +116,6 @@ class Request {
     webidl.argumentLengthCheck(arguments, 1, prefix)
 
     input = webidl.converters.RequestInfo(input)
-    // Capture this before WebIDL conversion fills dictionary defaults.
-    const initHasKey = requestInitHasUserMembers(init)
     init = webidl.converters.RequestInit(init)
 
     // 1. Let request be null.
@@ -276,6 +241,8 @@ class Request {
       urlList: [...request.urlList]
     })
 
+    const initHasKey = Object.keys(init).length !== 0
+
     // 13. If init is not empty, then:
     if (initHasKey) {
       // 1. If request’s mode is "navigate", then set it to "same-origin".
@@ -956,7 +923,7 @@ function makeRequest (init) {
     serviceWorkers: init.serviceWorkers ?? 'all',
     initiator: init.initiator ?? '',
     destination: init.destination ?? '',
-    priority: init.priority ?? null,
+    priority: init.priority ?? 'auto',
     origin: init.origin ?? 'client',
     policyContainer: init.policyContainer ?? 'client',
     referrer: init.referrer ?? 'client',
@@ -1162,8 +1129,7 @@ webidl.converters.RequestInit = webidl.dictionaryConverter([
   {
     key: 'priority',
     converter: webidl.converters.DOMString,
-    allowedValues: ['high', 'low', 'auto'],
-    defaultValue: () => 'auto'
+    allowedValues: ['high', 'low', 'auto']
   }
 ])
 

test/fetch/request.js

@@ -420,10 +420,11 @@ test('request.referrer', (t) => {
   }
 })
 
-// Dictionary defaults (undici's priority: "auto") must not make an omitted
-// RequestInit count as non-empty. That used to force a header clone/clear
-// on every fetch(url) / new Request(url) and reset copied request state.
-test('omitted RequestInit is empty even though priority defaults to auto', (t) => {
+// RequestInit.priority must not have a WebIDL default. A converter default
+// of "auto" made every omitted init non-empty (Object.keys never empty),
+// which cloned/cleared headers on fetch(url) / new Request(url) and reset
+// copied request state.
+test('omitted RequestInit is empty', (t) => {
   const parent = new Request('http://localhost/a', {
     method: 'POST',
     body: 'hi',