Discrepancy in json returned by fts `SNIPPET` function

[Zarux]

When using the fts SNIPPET function the emulator's output schema diverges from what production spanner produces.

Specifically, the emulator Returns start_position and end_position as keys inside the highlights array (https://github.com/GoogleCloudPlatform/cloud-spanner-emulator/blob/master/backend/query/search/snippet_evaluator.cc#L59-L60), whereas production returns begin and end.

And it entirely omits the source_begin and source_end keys at the snippet level (https://github.com/GoogleCloudPlatform/cloud-spanner-emulator/blob/master/backend/query/search/snippet_evaluator.cc#L202)

Given a query like

SELECT
  SNIPPET(content, "test"),
FROM
  test_table
WHERE
  SEARCH(content_tokens, "test")

Production spanner returns

{
   "snippets":[
      {
         "highlights":[
            {
               "begin":1,
               "end":5
            }
         ],
         "snippet":"Test est",
         "source_begin":1,
         "source_end":9
      }
   ]
}

This matches what is documented here https://docs.cloud.google.com/spanner/docs/reference/standard-sql/search_functions#snippet

The same query against the emulator returns

{
   "snippets":[
      {
         "highlights":[
            {
               "start_position":1,
               "end_position":5
            }
         ],
         "snippet":"Test est"
      }
   ]
}

Running Spanner Emulator Version: 1.5.54

Because of this discrepancy, application code and deserializers that work in production fail during local testing against the emulator unless environment-specific workarounds are added.

It would be nice if this could be fixed so the emulator returns the snippets using the same schema as production spanner.