[#14909] Fix for duplicate key isue when diffing catalogs with arrays

[jackie-numerade]

What

Fix for duplicateKeyException thrown when diffing catalogs that contain arrays in the schema (see #14909 ). This exception is due to the CatalogHelpers.getFullyQualifiedFieldNamesWithTypes() method returning the same names for both the array node and also the child "items" node, causing a collision during Stream.collect()' in CatalogHelpers.getStreamDiff()`.

Please see the updated unit test and also #14460 for examples of schemas that trigger this exception with the existing code.

How

The issue was caused by getFullyQualifiedFieldNamesWithTypes() filtering out the FieldNameOrList instances from the path list (so that the "items" node ends up with the same name list as the parent array node). The proposed fix here just adds a string "items" to the name list instead of ignoring that list instance altogether. However, this does introduce a new "items" node that could be included in the final Catalog diff. I honestly don't know how/where this diff is used upstream (including the frontend), so I'm not sure if this would cause any issues.

Another alternative would be to just exclude either the array node or the "items" node from the result of the getFullyQualifiedFieldNamesWithTypes() method. The only downside to that approach is that it wouldn't be able to detect diffs in cases where an array field turned into an object field (with the same child schema), or vice versa, since the resulting field list would look the same (though this is probably an edge case).

Recommended reading order

1. CatalogHelpers.java
2. CatalogHelpersTest.java

🚨 User Impact 🚨

Unknown, depending on how/where the results of CatalogHelpers.getCatalogDiff() are used.

Close #14909

[CLAassistant]

All committers have signed the CLA.

[evantahler]

Thank you for this fix & the tests! This looks 👍 to me, but tagging @jdpgrailsdev for review as well, who knows a lot more about Java than I do.

[jdpgrailsdev]