Filter don't delete tail nodes of forms

This lets us put extra data to encode actions at the end.

Author: sebmarkbage

packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js

@@ -89,6 +89,7 @@ import {
   enableHostSingletons,
   enableTrustedTypesIntegration,
   diffInCommitPhase,
+  enableFormActions,
 } from 'shared/ReactFeatureFlags';
 import {
   HostComponent,
@@ -1419,12 +1420,14 @@ export function commitHydratedSuspenseInstance(
   retryIfBlockedOn(suspenseInstance);
 }
 
-// @TODO remove this function once float lands and hydrated tail nodes
-// are controlled by HostSingleton fibers
 export function shouldDeleteUnhydratedTailInstances(
   parentType: string,
 ): boolean {
-  return parentType !== 'head' && parentType !== 'body';
+  return (
+    (enableHostSingletons ||
+      (parentType !== 'head' && parentType !== 'body')) &&
+    (!enableFormActions || parentType !== 'form')
+  );
 }
 
 export function didNotMatchHydratedContainerTextInstance(

packages/react-reconciler/src/ReactFiberHydrationContext.js

@@ -802,7 +802,8 @@ function popHydrationState(fiber: Fiber): boolean {
       fiber.tag !== HostSingleton &&
       !(
         fiber.tag === HostComponent &&
-        shouldSetTextContent(fiber.type, fiber.memoizedProps)
+        (!shouldDeleteUnhydratedTailInstances(fiber.type) ||
+          shouldSetTextContent(fiber.type, fiber.memoizedProps))
       )
     ) {
       shouldClear = true;