Filter date for a field entry to use in the slug

[p3lican]

I'd like to inject a "Game or Event Year" into the slug. Rather than creating fields for day and year, I'd like to be able to strip the year from the single "Event Date" field entry and use that in my slug.

Basically exactly what you have done for summaries: https://www.netlifycms.org/docs/beta-features/#summary-string-template-transformations.

collections:
  - label: "Games"
    name: "games"
    folder: "content/games"
    create: true
    identifier_field: gamenumber
    slug: 'game-{{gamenumber}}-{{opponent.teamname}}-{{gamedate | date('YYYY')}}' <-- something like that
    format: 'json'
    fields:
      - {label: "Game Number", name: "gamenumber", widget: "string"}
      - {label: "Game Date", name: "gamedate", widget: "datetime"}

[erezrokah]

To add some more context, one can inject the file creation date using {{year}}:
https://www.netlifycms.org/docs/configuration-options/#slug

but this issue is about using a specific field's date and formatting it.

[p4r4noj4]

Any idea if this is going to be done (or if it's hard to do)? It looks like a no-brainer since there is already https://www.netlifycms.org/docs/beta-features/#summary-string-template-transformations .