fix: provide custom error for FieldValue subclasses (#771)

This PR extends the custom errors for instances of FieldValue classes that do not match the expected prototype to the FieldValue sentinel classes FieldTransform, ServerTimestampTransform, ArrayUnionTransform, ArrayRemoveTransform and NumericIncrementTransform.

Fixes #760

dev/src/validate.ts

@@ -37,6 +37,22 @@ export interface NumericRangeOptions {
   maxValue?: number;
 }
 
+/**
+ * Returns the name of the base class (ignoring Object).
+ *
+ * @private
+ * @param value The object whose base class name to extract.
+ * @returns The name of the base class constructor or "Object" if value does not
+ * extend a custom class.
+ */
+function extractBaseClassName(value: object): string {
+  let constructorName = 'Object';
+  while (Object.getPrototypeOf(value) !== Object.prototype) {
+    value = Object.getPrototypeOf(value);
+    constructorName = value.constructor.name;
+  }
+  return constructorName;
+}
 /**
  * Generates an error message to use with custom objects that cannot be
  * serialized.
@@ -54,7 +70,10 @@ export function customObjectMessage(
   const fieldPathMessage = path ? ` (found in field ${path})` : '';
 
   if (isObject(value)) {
-    const typeName = value.constructor.name;
+    // We use the base class name as the type name as the sentinel classes
+    // returned by the public FieldValue API are subclasses of FieldValue. By
+    // using the base name, we reduce the number of special cases below.
+    const typeName = extractBaseClassName(value);
     switch (typeName) {
       case 'DocumentReference':
       case 'FieldPath':

dev/test/document.ts

@@ -170,6 +170,29 @@ describe('serialize document', () => {
     );
   });
 
+  it('provides custom error for objects from different Firestore instance', () => {
+    class FieldPath {}
+    class CustomFieldPath extends FieldPath {}
+    class VeryCustomFieldPath extends CustomFieldPath {}
+
+    const customClasses = [
+      new FieldPath(),
+      new CustomFieldPath(),
+      new VeryCustomFieldPath(),
+    ];
+
+    for (const customClass of customClasses) {
+      expect(() => {
+        firestore
+          .doc('collectionId/documentId')
+          .set(customClass as InvalidApiUsage);
+      }).to.throw(
+        'Value for argument "data" is not a valid Firestore document. ' +
+          'Detected an object of type "FieldPath" that doesn\'t match the expected instance.'
+      );
+    }
+  });
+
   it('serializes large numbers into doubles', () => {
     const overrides: ApiOverride = {
       commit: (request, options, callback) => {