## Optimize validateParentPath for Faster Parent Path Validation (#1396)

This commit refactors the `validateParentPath` function in `transaction-shim.ts` to improve its performance, especially for deep or frequent path validations during storage transactions.

### Optimization Details

- **Single-pass Traversal:**
  The previous implementation redundantly checked object-ness and existence at each path level, sometimes re-traversing the same objects. The new approach streamlines the traversal by iterating through the parent path only once, directly walking down the value tree and stopping at the first missing or non-object parent.

- **Efficient Error Handling:**
  Error construction is now more precise, and the function avoids unnecessary object checks and array slicing. The logic for setting the error's `.path` property is simplified, reducing overhead in error cases.

- **No Change in Behavior:**
  All existing functionality and error semantics are preserved. The function still returns the same errors for invalid paths, but does so with less computational overhead.

Author: seefeldb

packages/runner/src/storage/transaction-shim.ts

@@ -51,12 +51,14 @@ function validateParentPath(
   value: any,
   path: readonly MemoryAddressPathComponent[],
 ): INotFoundError | null {
-  if (path.length === 0) {
+  const pathLength = path.length;
+
+  if (pathLength === 0) {
     return null; // Root write, no validation needed
   }
 
-  // Check if the document itself exists and is a record for first-level writes
-  if (path.length === 1) {
+  // Check if the document itself exists and is an object for first-level writes
+  if (pathLength === 1) {
     if (value === undefined || !isRecord(value)) {
       const pathError: INotFoundError = new Error(
         `Cannot access path [${String(path[0])}] - document is not a record`,
@@ -67,33 +69,31 @@ function validateParentPath(
     return null;
   }
 
-  // For deeper paths, check that the parent path exists and is a record
-  const parentPath = path.slice(0, -1);
+  // For deeper paths, check that the parent path exists and is an object
+  const lastIndex = pathLength - 1;
+  let parentValue = value;
 
-  const parentValue = getValueAtPath(value, parentPath);
+  let parentIndex = 0;
+  for (parentIndex = 0; parentIndex < lastIndex; parentIndex++) {
+    if (!isRecord(parentValue)) {
+      parentValue = undefined;
+      break;
+    }
+    parentValue = parentValue[path[parentIndex] as keyof typeof parentValue];
+  }
 
   if (
     value === undefined || parentValue === undefined || !isRecord(parentValue)
   ) {
     const pathError: INotFoundError = new Error(
-      `Cannot access path [${
-        path.map((p) => String(p)).join(", ")
-      }] - parent path [${
-        parentPath.map((p) => String(p)).join(", ")
+      `Cannot access path [${path.join(", ")}] - parent path [${
+        path.slice(0, lastIndex).join(", ")
       }] does not exist or is not a record`,
     ) as INotFoundError;
     pathError.name = "NotFoundError";
 
     // Set pathError.path to last valid parent path component
-    if (isRecord(value)) {
-      pathError.path = [];
-      while (parentPath.length > 0) {
-        const segment = parentPath.shift()!;
-        value = value[segment];
-        if (!isRecord(value)) break;
-        pathError.path.push(segment);
-      }
-    }
+    if (parentIndex > 0) pathError.path = path.slice(0, parentIndex - 1);
 
     return pathError;
   }
@@ -567,10 +567,10 @@ export class ExtendedStorageTransaction implements IExtendedStorageTransaction {
     if (writeResult.error && writeResult.error.name === "NotFoundError") {
       // Create parent entries if needed
       const lastValidPath = writeResult.error.path;
-      const valueObj = (lastValidPath
+      const valueObj = lastValidPath
         ? this.readValueOrThrow({ ...address, path: lastValidPath })
-        : {}) as Record<string, any>;
-      if (!isObject(valueObj)) {
+        : {};
+      if (!isRecord(valueObj)) {
         throw new Error(
           `Value at path ${address.path.join("/")} is not an object`,
         );
@@ -584,7 +584,9 @@ export class ExtendedStorageTransaction implements IExtendedStorageTransaction {
       const lastKey = remainingPath.pop()!;
       let nextValue = valueObj;
       for (const key of remainingPath) {
-        nextValue = nextValue[key] = typeof Number(key) === "number" ? [] : {};
+        nextValue =
+          nextValue[key] =
+            (typeof Number(key) === "number" ? [] : {}) as typeof nextValue;
       }
       nextValue[lastKey] = value;
       const parentAddress = { ...address, path: lastValidPath ?? [] };