fetch: warn when using patch method

lib/fetch/request.js

@@ -38,6 +38,8 @@ const requestFinalizer = new FinalizationRegistry(({ signal, abort }) => {
   signal.removeEventListener('abort', abort)
 })
 
+let patchMethodWarning = false
+
 // https://fetch.spec.whatwg.org/#request-class
 class Request {
   // https://fetch.spec.whatwg.org/#dom-request
@@ -335,6 +337,14 @@ class Request {
         // 4. Set request’s method to method.
         request.method = method
       }
+
+      if (!patchMethodWarning && request.method === 'patch') {
+        process.emitWarning('Using `patch` is highly likely to result in a `405 Method Not Allowed`. `PATCH` is much more likely to succeed.', {
+          code: 'UNDICI-FETCH-patch'
+        })
+
+        patchMethodWarning = true
+      }
     }
 
     // 26. If init["signal"] exists, then set signal to it.

test/fetch/issue-2294-patch-method.js

@@ -0,0 +1,21 @@
+'use strict'
+
+const { test } = require('tap')
+const { Request } = require('../..')
+
+test('Using `patch` method emits a warning.', (t) => {
+  t.plan(1)
+
+  const { emitWarning } = process
+
+  t.teardown(() => {
+    process.emitWarning = emitWarning
+  })
+
+  process.emitWarning = (warning, options) => {
+    t.equal(options.code, 'UNDICI-FETCH-patch')
+  }
+
+  // eslint-disable-next-line no-new
+  new Request('https://a', { method: 'patch' })
+})