ArangoSearch unable to retrieve offset info for nested fields

[etiennecl]

My Environment

• ArangoDB Version: 3.11.1
• Deployment Mode: Single Server
• Deployment Strategy: ArangoDB Starter in Docker
• Configuration:
• Infrastructure: Macbook Pro M1
• Operating System: MacOS 12.6.5
• Total RAM in your machine: 32Gb
• Disks in use: SSD

Component, Query & Data

Affected feature: ArangoSearch OFFSET_INFO

AQL query (if applicable):

FOR doc IN `index`
    SEARCH doc.nested[? 
        FILTER CURRENT.key == 'gh' AND STARTS_WITH(CURRENT.value, 'montre') 
    ]
    LIMIT 100
    FOR offsetInfo IN OFFSET_INFO(doc, ['nested[*].value'])
        RETURN {
            name: offsetInfo.name,
            matches: offsetInfo.offsets[* RETURN {
                offset: CURRENT,
                match: SUBSTRING_BYTES(VALUE(doc, offsetInfo.name), CURRENT[0], CURRENT[1])
            }]
        }

Dataset:
All documents have the following shape

{
  "type": "abc",
  "nested": [
     {
       "key": "gh",
       "value": "montreal"
     },

     {
       "key": "yz",
       "value": "quebec"
     }
  ]
}

Steps to reproduce

1. Create the following alias

{
    "name": "plain",
    "type": "norm",
    "features": [
        "frequency",
        "position",
        "offset",
        "norm"
    ],
    "properties": {
        "locale": "en",
        "case": "lower",
        "accent": false
    }
}

2. Create the following inverted-index collection_a_index over collection collection_a

{
  "searchField": true,
  "trackListPositions": true,
  "fields": [
    {
      "name": "type",
      "analyzez": "plain"
    },
    {
       "name": "nested",
       "nested": [
         {
           "name": "key"
         },
         {
           "name": "value"
           "analyzer": "plain"
         }
       ]
    }
  ]
}

3. Create the following search alias

{
  "type": "search-alias",
  "name": "index",
  "indexes": [
    {
      "collection": "collection_a",
      "index": "collection_a_index"
    }
  ]
}

Problem:

Getting the offset info for nested properties does not work.

Expected result:

I would expect arango to allow getting offset info when matching using nested search.