tighten up types for server action metadata

Author: lubieowoce

Diff for: packages/next/src/server/app-render/action-handler.ts

@@ -870,12 +870,6 @@ export async function handleAction({
           console.error(err)
           return { type: 'not-found' }
         }
-        if (actionId === null) {
-          // `getActionModIdOrError` checks this, but typescript doesn't know that.
-          throw new InvariantError(
-            'Expected actionId to be defined for a fetch action'
-          )
-        }
 
         // The temporary reference set is used for parsing the arguments and in the catch handler,
         // so we want to create it before any of the decoding logic has a chance to throw.

Diff for: packages/next/src/server/lib/server-action-request-meta.ts

@@ -3,15 +3,25 @@ import type { BaseNextRequest } from '../base-http'
 import type { NextRequest } from '../web/exports'
 import { ACTION_HEADER } from '../../client/components/app-router-headers'
 
+export type ServerActionRequestMetadata =
+  | {
+      isFetchAction: true
+      actionId: string
+      isURLEncodedAction: boolean
+      isMultipartAction: boolean
+      isPotentialServerAction: true
+    }
+  | {
+      isFetchAction: false
+      actionId: null
+      isURLEncodedAction: boolean
+      isMultipartAction: boolean
+      isPotentialServerAction: boolean
+    }
+
 export function getServerActionRequestMetadata(
   req: IncomingMessage | BaseNextRequest | NextRequest
-): {
-  actionId: string | null
-  isURLEncodedAction: boolean
-  isMultipartAction: boolean
-  isFetchAction: boolean
-  isPotentialServerAction: boolean
-} {
+): ServerActionRequestMetadata {
   let actionId: string | null
   let contentType: string | null
 
@@ -29,21 +39,26 @@ export function getServerActionRequestMetadata(
   const isMultipartAction = Boolean(
     req.method === 'POST' && contentType?.startsWith('multipart/form-data')
   )
-  const isFetchAction = Boolean(
-    actionId !== undefined &&
-      typeof actionId === 'string' &&
-      req.method === 'POST'
-  )
+  if (actionId !== null && req.method === 'POST') {
+    return {
+      isFetchAction: true,
+      actionId,
+      isMultipartAction,
+      isURLEncodedAction,
+      isPotentialServerAction: true,
+    }
+  }
 
   const isPotentialServerAction = Boolean(
-    isFetchAction || isURLEncodedAction || isMultipartAction
+    isURLEncodedAction || isMultipartAction
   )
 
   return {
-    actionId,
+    isFetchAction: false,
+    // it may technically be non-null, but there's no use for it outside a fetch action.
+    actionId: null,
     isURLEncodedAction,
     isMultipartAction,
-    isFetchAction,
     isPotentialServerAction,
   }
 }