[labs/ssr-client] Avoid nullish logical assignment in hydrate-lit-html (#4312)

augustjk · rictic · web-flow · commit 26182733046e · 2023-10-20T13:38:13.000-07:00
Co-authored-by: Peter Burns &lt;rictic@google.com&gt;
diff --git a/.changeset/olive-otters-vanish.md b/.changeset/olive-otters-vanish.md
@@ -0,0 +1,5 @@
+---
+'@lit-labs/ssr-client': patch
+---
+
+Avoid nullish logical assignment in hydrate-lit-html which some minification process would not handle correctly. Fixes hydration errors in Next.js production bundles.
diff --git a/packages/labs/ssr-client/src/lib/hydrate-lit-html.ts b/packages/labs/ssr-client/src/lib/hydrate-lit-html.ts
@@ -163,7 +163,12 @@ export const hydrate = (
       }
       // Create a new ChildPart and push it onto the stack
       currentChildPart = openChildPart(rootValue, marker, stack, options);
-      rootPart ??= currentChildPart;
+      // Using nullish logical assignment below can cause next.js's swc to move
+      // the `openChildPart()` call above behind the nullish check.
+      // See https://github.com/lit/lit/issues/4289
+      if (rootPart === undefined) {
+        rootPart = currentChildPart;
+      }
       rootPartMarker ??= marker;
     } else if (markerText.startsWith('lit-node')) {
       // Create and hydrate attribute parts into the current ChildPart on the

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'@lit-labs/ssr-client': patch
 +---
++
 +Avoid nullish logical assignment in hydrate-lit-html which some minification process would not handle correctly. Fixes hydration errors in Next.js production bundles.