selection on fields=[fieldname:N] generates :N in vega-lite fields but should not

Copied from https://github.com/vega/vega-lite/issues/5710:

if I call selection = alt.selection_multi(fields=["advance_mode:N"], bind='legend'), Altair 4.0.0 generates

"selection": {
    "selector009": {
      "type": "multi",
      "fields": ["advance_mode:N"],
      "bind": "legend"
    },

but I believe it should drop the :N and generate

"selection": {
    "selector009": {
      "type": "multi",
      "fields": ["advance_mode"],
      "bind": "legend"
    },

The latter has the intended behavior AFAICT.

[jakevdp]

The reason Altair doesn’t do this automatically is because it requires assuming too much about user intent. For example, it’s possible to have dataframe columns with colons in their names.

We could go down the rabbit hole of checking dataframe column names against specified field names to try and infer the intent of the user, but then what about remote data? And what about transforms that define new data fields? There are a ton of potentially surprising corner cases and pitfalls as soon as you try to infer user intent from incomplete information, and so Altair has chosen to avoid that. As they say, explicit is better than implicit.

[jowens]

Totally sensible. I appreciate the explanation!