fix(NODE-6276): preserve top level error code MongoWriteConcernError

src/bulk/common.ts

@@ -616,8 +616,8 @@ function handleMongoWriteConcernError(
   callback(
     new MongoBulkWriteError(
       {
-        message: err.result?.writeConcernError.errmsg,
-        code: err.result?.writeConcernError.result
+        message: err.result.writeConcernError.errmsg,
+        code: err.result.writeConcernError.code
       },
       new BulkWriteResult(bulkResult, isOrdered)
     )

src/error.ts

@@ -1158,6 +1158,23 @@ export class MongoServerSelectionError extends MongoSystemError {
   }
 }
 
+/**
+ * The type of the result property of MongoWriteConcernError
+ * @public
+ */
+export interface WriteConcernErrorResult {
+  writeConcernError: {
+    code: number;
+    errmsg: string;
+    codeName?: string;
+    errInfo?: Document;
+  };
+  ok: number;
+  code?: number;
+  errorLabels?: string[];
+  [x: string | number]: unknown;
+}
+
 /**
  * An error thrown when the server reports a writeConcernError
  * @public
@@ -1178,16 +1195,8 @@ export class MongoWriteConcernError extends MongoServerError {
    *
    * @public
    **/
-  constructor(result: {
-    writeConcernError: {
-      code: number;
-      errmsg: string;
-      codeName?: string;
-      errInfo?: Document;
-    };
-    errorLabels?: string[];
-  }) {
-    super({ ...result, ...result.writeConcernError });
+  constructor(result: WriteConcernErrorResult) {
+    super({ ...result.writeConcernError, ...result });
     this.errInfo = result.writeConcernError.errInfo;
     this.result = result;
   }
@@ -1237,7 +1246,7 @@ export function needsRetryableWriteLabel(error: Error, maxWireVersion: number):
   }
 
   if (error instanceof MongoWriteConcernError) {
-    return RETRYABLE_WRITE_ERROR_CODES.has(error.result?.code ?? error.code ?? 0);
+    return RETRYABLE_WRITE_ERROR_CODES.has(error.result.writeConcernError.code ?? error?.code ?? 0);
   }
 
   if (error instanceof MongoError && typeof error.code === 'number') {

src/index.ts

@@ -73,7 +73,8 @@ export {
   MongoTopologyClosedError,
   MongoTransactionError,
   MongoUnexpectedServerResponseError,
-  MongoWriteConcernError
+  MongoWriteConcernError,
+  WriteConcernErrorResult
 } from './error';
 export {
   AbstractCursor,

test/unit/error.test.ts

@@ -740,4 +740,33 @@ describe('MongoErrors', () => {
       });
     });
   });
+
+  describe('MongoWriteConcernError constructor', function () {
+    context('when no top-level code is provided', function () {
+      it('error.code is set to writeConcernError.code', function () {
+        const res = {
+          writeConcernError: {
+            code: 81, // nested code
+            errmsg: 'fake msg'
+          },
+          ok: 1
+        };
+        expect(new MongoWriteConcernError(res).code).to.equal(81);
+      });
+    });
+    context('when top-level code is provided and  writeConcernError.code exists', function () {
+      it('error.code equals the top-level code', function () {
+        const topLevelCode = 10;
+        const res = {
+          writeConcernError: {
+            code: 81, // nested code
+            errmsg: 'fake msg'
+          },
+          ok: 1,
+          code: topLevelCode
+        };
+        expect(new MongoWriteConcernError(res).code).to.equal(topLevelCode);
+      });
+    });
+  });
 });

test/unit/index.test.ts

@@ -108,6 +108,7 @@ const EXPECTED_EXPORTS = [
   'MongoTransactionError',
   'MongoUnexpectedServerResponseError',
   'MongoWriteConcernError',
+  'WriteConcernErrorResult',
   'ObjectId',
   'OrderedBulkOperation',
   'ProfilingLevel',