[LUCENE-10290] analysis-stempel incorrect tokens generation for numbers

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 8.7
• Component/s: modules/analysis

Environment

*Elasticsearch version* 7.11.2:

*Plugins installed*: [analysis-stempel]

*OS version* CentOS

• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Dominik
• Created: 06/Dec/21 13:50
• Updated: 28/Aug/22 16:32

Description

Actual:
I observed unexpected behaviour. Some numbers are affected by stemmer. It causes wrong search results.
For example "2021" -> "20ć".

Expected:
string numbers should not be changed.

Reproduce:

Issue can be reproduced with elasticsearch:

request:

POST _analyze
{
  "tokenizer": "standard",
  "filter": ["polish_stem"],
  "text": "2021"
}

response:

{
  "tokens": [
    {
      "token": "20ć",
      "start_offset": 0,
      "end_offset": 4,
      "type": "<NUM>",
      "position": 0
    }
  ]
}

I suspect the newer versions are also affected, but I don't have possibility to verify it.