Throw proper error for FieldValue transforms in arrays (#3183)

Author: schmidt-sebastian

packages/firestore/src/api/user_data_reader.ts

@@ -623,7 +623,7 @@ function parseSentinelFieldValue(
       `${value._methodName}() can only be used with update() and set()`
     );
   }
-  if (context.path === null) {
+  if (!context.path) {
     throw context.createError(
       `${value._methodName}() is not currently supported inside arrays`
     );

packages/firestore/test/integration/api/validation.test.ts

@@ -470,6 +470,18 @@ apiDescribe('Validation:', (persistence: boolean) => {
       }
     );
 
+    validationIt(
+      persistence,
+      'must not contain field value transforms in arrays',
+      db => {
+        return expectWriteToFail(
+          db,
+          { 'array': [FieldValue.serverTimestamp()] },
+          'FieldValue.serverTimestamp() is not currently supported inside arrays'
+        );
+      }
+    );
+
     validationIt(
       persistence,
       'must not contain directly nested arrays.',