Modify collectConflictsBetweenFieldsAndFragment() to track seen fragm…

…ents when recursing into fragments (but not when recursing into fields, to save memory)

src/validation/rules/OverlappingFieldsCanBeMergedRule.ts

@@ -200,6 +200,7 @@ function findConflictsWithinSelectionSet(
         conflicts,
         cachedFieldsAndFragmentNames,
         comparedFragmentPairs,
+        null,
         false,
         fieldMap,
         fragmentNames[i],
@@ -231,10 +232,15 @@ function collectConflictsBetweenFieldsAndFragment(
   conflicts: Array<Conflict>,
   cachedFieldsAndFragmentNames: Map<SelectionSetNode, FieldsAndFragmentNames>,
   comparedFragmentPairs: PairSet,
+  comparedFragmentsForFields: null | Set<string>,
   areMutuallyExclusive: boolean,
   fieldMap: NodeAndDefCollection,
   fragmentName: string,
 ): void {
+  if (comparedFragmentsForFields?.has(fragmentName)) {
+    return;
+  }
+
   const fragment = context.getFragment(fragmentName);
   if (!fragment) {
     return;
@@ -266,12 +272,15 @@ function collectConflictsBetweenFieldsAndFragment(
 
   // (E) Then collect any conflicts between the provided collection of fields
   // and any fragment names found in the given fragment.
+  const newComparedFragmentsForFields =
+    comparedFragmentsForFields ?? new Set([fragmentName]);
   for (const referencedFragmentName of referencedFragmentNames) {
     collectConflictsBetweenFieldsAndFragment(
       context,
       conflicts,
       cachedFieldsAndFragmentNames,
       comparedFragmentPairs,
+      newComparedFragmentsForFields,
       areMutuallyExclusive,
       fieldMap,
       referencedFragmentName,
@@ -414,6 +423,7 @@ function findConflictsBetweenSubSelectionSets(
       conflicts,
       cachedFieldsAndFragmentNames,
       comparedFragmentPairs,
+      null,
       areMutuallyExclusive,
       fieldMap1,
       fragmentName2,
@@ -428,6 +438,7 @@ function findConflictsBetweenSubSelectionSets(
       conflicts,
       cachedFieldsAndFragmentNames,
       comparedFragmentPairs,
+      null,
       areMutuallyExclusive,
       fieldMap2,
       fragmentName1,