unrecognized signal name: "PARAM_tuple_fields" using "bind": {"input": "checkbox"}

[mattijn]

As was raised in vega/altair#2856.
Given the following minimal Vega-Lite specification (Open the Chart in the Vega Editor):

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.2.0.json",
  "data": {"values": [{}]},
  "encoding": {
    "size": {"condition": {"param": "PARAM", "value": 25}, "value": 100}
  },
  "mark": "point",
  "params": [
    {
      "bind": {"input": "checkbox"},
      "name": "PARAM",
      "select": {"type": "point"}
    }
  ]
}

It currently gives an error in the Vega-Editor:

Unrecognized signal name: "PARAM_tuple_fields"

It still renders in Altair (why it still renders using the main branch of Altair is also not crystal clear, since it should be equal to what the Vega-Editor is using currently..), but the interaction only works once.

[mattijn]

As this spec rendered fine in VL5.2, this feels like an introduced regression somewhere in between VL5.2 and VL5.6.1.

[mattijn]

Explained in more detail here vega/altair#2871 (comment) and/or Open the Chart in the Vega Editor.

[mattijn]

Already resolved by #4870 (comment)