fix(delegate): handle existing argument nodes correctly

Author: ardatan

.changeset/cold-files-drive.md

@@ -0,0 +1,6 @@
+---
+'@graphql-tools/delegate': patch
+'@graphql-tools/utils': patch
+---
+
+Fix handling argument values in gateway request

packages/delegate/src/finalizeGatewayRequest.ts

@@ -16,6 +16,7 @@ import {
   SelectionSetNode,
   TypeInfo,
   TypeNameMetaFieldDef,
+  valueFromAST,
   VariableDefinitionNode,
   versionInfo as graphqlVersionInfo,
   visit,
@@ -221,14 +222,22 @@ function updateArguments(
     const argType = argument.type;
 
     if (argName in newArgs) {
+      let value: any;
+      const existingValueNode = argumentNodeMap[argName]?.value;
+      if (existingValueNode != null) {
+        value = valueFromAST(existingValueNode, argType, variableValues);
+      }
+      if (value == null) {
+        value = serializeInputValue(argType, newArgs[argName]);
+      }
       updateArgument(
         argumentNodeMap,
         variableDefinitionMap,
         variableValues,
         argName,
         generateVariableName(argName),
         argType,
-        serializeInputValue(argType, newArgs[argName])
+        value
       );
     }
   }

packages/utils/src/transformInputValue.ts

@@ -1,4 +1,5 @@
 import { GraphQLInputType, getNullableType, isLeafType, isListType, isInputObjectType } from 'graphql';
+import { asArray } from './helpers.js';
 
 import { InputLeafValueTransformer, InputObjectValueTransformer, Maybe } from './types.js';
 
@@ -17,7 +18,7 @@ export function transformInputValue(
   if (isLeafType(nullableType)) {
     return inputLeafValueTransformer != null ? inputLeafValueTransformer(nullableType, value) : value;
   } else if (isListType(nullableType)) {
-    return value.map((listMember: any) =>
+    return asArray(value).map((listMember: any) =>
       transformInputValue(nullableType.ofType, listMember, inputLeafValueTransformer, inputObjectValueTransformer)
     );
   } else if (isInputObjectType(nullableType)) {