Check root.hydrate before scheduling root to be cleared

This avoids breaking support for ReactDOM.hydration in legacy mode with no fallback.
facebook · Apr 27, 2020 · f318360 · f318360
1 parent 317fb78
commit f318360
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Showing 2 changed files with 6 additions and 2 deletions.
diff --git a/packages/react-reconciler/src/ReactFiberCompleteWork.new.js b/packages/react-reconciler/src/ReactFiberCompleteWork.new.js
@@ -681,11 +681,13 @@ function completeWork(
           // If we hydrated, then we'll need to schedule an update for
           // the commit side-effects on the root.
           markUpdate(workInProgress);
-        } else {
+        } else if (!fiberRoot.hydrate) {
           // Schedule an effect to clear this container at the start of the next commit.
           // This handles the case of React rendering into a container with previous children.
           // It's also safe to do for updates too, because current.child would only be null
           // if the previous render was null (so the the container would already be empty).
+          //
+          // The additional root.hydrate check is required for hydration in legacy mode with no fallback.
           workInProgress.effectTag |= Snapshot;
         }
       }

diff --git a/packages/react-reconciler/src/ReactFiberCompleteWork.old.js b/packages/react-reconciler/src/ReactFiberCompleteWork.old.js
@@ -679,11 +679,13 @@ function completeWork(
           // If we hydrated, then we'll need to schedule an update for
           // the commit side-effects on the root.
           markUpdate(workInProgress);
-        } else {
+        } else if (!fiberRoot.hydrate) {
           // Schedule an effect to clear this container at the start of the next commit.
           // This handles the case of React rendering into a container with previous children.
           // It's also safe to do for updates too, because current.child would only be null
           // if the previous render was null (so the the container would already be empty).
+          //
+          // The additional root.hydrate check is required for hydration in legacy mode with no fallback.
           workInProgress.effectTag |= Snapshot;
         }
       }