Fix a memory leak with the shared TreeWalker (#3888)

lit · May 9, 2023 · 0f30e6f · 0f30e6f
1 parent 55148f8
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diff --git a/.changeset/few-feet-design.md b/.changeset/few-feet-design.md
@@ -0,0 +1,5 @@
+---
+'lit-html': patch
+---
+
+Fix a memory leak cause by lit-html's shared TreeWalker holding a reference to the last tree it walked.
diff --git a/packages/lit-html/src/lit-html.ts b/packages/lit-html/src/lit-html.ts
@@ -1005,6 +1005,9 @@ class Template {
       }
       nodeIndex++;
     }
+    // We could set walker.currentNode to another node here to prevent a memory
+    // leak, but every time we prepare a template, we immediately render it
+    // and re-use the walker in new TemplateInstance._clone().
     debugLogEvent?.({
       kind: 'template prep',
       template: this,
@@ -1155,6 +1158,10 @@ class TemplateInstance implements Disconnectable {
         nodeIndex++;
       }
     }
+    // We need to set the currentNode away from the cloned tree so that we
+    // don't hold onto the tree even if the tree is detached and should be
+    // freed.
+    walker.currentNode = d;
     return fragment;
   }