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server/node_modules/graphql/validation/rules/UniqueInputFieldNames.js.flow

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+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import type { ASTValidationContext } from '../ValidationContext';
+import { GraphQLError } from '../../error/GraphQLError';
+import type { ASTVisitor } from '../../language/visitor';
+
+export function duplicateInputFieldMessage(fieldName: string): string {
+  return `There can be only one input field named "${fieldName}".`;
+}
+
+/**
+ * Unique input field names
+ *
+ * A GraphQL input object value is only valid if all supplied fields are
+ * uniquely named.
+ */
+export function UniqueInputFieldNames(
+  context: ASTValidationContext,
+): ASTVisitor {
+  const knownNameStack = [];
+  let knownNames = Object.create(null);
+
+  return {
+    ObjectValue: {
+      enter() {
+        knownNameStack.push(knownNames);
+        knownNames = Object.create(null);
+      },
+      leave() {
+        knownNames = knownNameStack.pop();
+      },
+    },
+    ObjectField(node) {
+      const fieldName = node.name.value;
+      if (knownNames[fieldName]) {
+        context.reportError(
+          new GraphQLError(duplicateInputFieldMessage(fieldName), [
+            knownNames[fieldName],
+            node.name,
+          ]),
+        );
+      } else {
+        knownNames[fieldName] = node.name;
+      }
+      return false;
+    },
+  };
+}