From 40f07e23d8396a02ad4ba99eb52c5d1f15ba6bc6 Mon Sep 17 00:00:00 2001
From: Yaacov Rydzinski <yaacovCR@gmail.com>
Date: Fri, 15 Dec 2023 08:23:38 +0200
Subject: [PATCH] remove permanent tracking of all ancestors

in favor of resolution at runtime

this is a tradeoff of theoretical performance gain vs code simplification
---
 src/execution/buildFieldPlan.ts | 14 +++++++++++++-
 src/execution/collectFields.ts  |  7 ++-----
 src/execution/execute.ts        |  3 +--
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/execution/buildFieldPlan.ts b/src/execution/buildFieldPlan.ts
index 42886d7ac6..48035e7886 100644
--- a/src/execution/buildFieldPlan.ts
+++ b/src/execution/buildFieldPlan.ts
@@ -77,7 +77,7 @@ export function buildFieldPlan(
     for (const target of targetSet) {
       if (
         target === undefined ||
-        target.ancestors.every((ancestor) => !targetSet.has(ancestor))
+        getAncestors(target).every((ancestor) => !targetSet.has(ancestor))
       ) {
         maskingTargetList.push(target);
       }
@@ -145,3 +145,15 @@ export function buildFieldPlan(
     newDeferUsages: Array.from(newDeferUsages),
   };
 }
+
+function getAncestors(
+  deferUsage: DeferUsage,
+): ReadonlyArray<DeferUsage | undefined> {
+  let parentDeferUsage: DeferUsage | undefined = deferUsage.parentDeferUsage;
+  const ancestors: Array<DeferUsage | undefined> = [parentDeferUsage];
+  while (parentDeferUsage !== undefined) {
+    parentDeferUsage = parentDeferUsage.parentDeferUsage;
+    ancestors.unshift(parentDeferUsage);
+  }
+  return ancestors;
+}
diff --git a/src/execution/collectFields.ts b/src/execution/collectFields.ts
index d5acdf8fbf..7625e1af18 100644
--- a/src/execution/collectFields.ts
+++ b/src/execution/collectFields.ts
@@ -28,7 +28,7 @@ import { getDirectiveValues } from './values.js';
 
 export interface DeferUsage {
   label: string | undefined;
-  ancestors: ReadonlyArray<DeferUsage | undefined>;
+  parentDeferUsage: DeferUsage | undefined;
 }
 
 export interface FieldDetails {
@@ -242,10 +242,7 @@ function getDeferUsage(
 
   return {
     label: typeof defer.label === 'string' ? defer.label : undefined,
-    ancestors:
-      parentDeferUsage === undefined
-        ? [undefined]
-        : [parentDeferUsage, ...parentDeferUsage.ancestors],
+    parentDeferUsage,
   };
 }
 
diff --git a/src/execution/execute.ts b/src/execution/execute.ts
index b710f68ff7..6442f7f0d0 100644
--- a/src/execution/execute.ts
+++ b/src/execution/execute.ts
@@ -1464,8 +1464,7 @@ function addNewDeferredFragments(
 
   // For each new deferUsage object:
   for (const newDeferUsage of newDeferUsages) {
-    // DeferUsage objects track their parent targets; the immediate parent is always the first member of this list.
-    const parentTarget = newDeferUsage.ancestors[0];
+    const parentTarget = newDeferUsage.parentDeferUsage;
 
     // If the parent target is defined, the parent target is a DeferUsage object and
     // the parent result record is the DeferredFragmentRecord corresponding to that DeferUsage.