3.0.0-rc0: strange schema for FoldTransform.as

[jakevdp]

The schema definition for FoldTransform.as is a bit strange. It's supposed to be a two-element array, correct? So what is the purpose of additionalItems: anyOf: ["string", "string"]?

I'm wondering if this is indicative of some mis-specification in the typescript.

[jakevdp]

Also, I'm not certain what vega-lite version the currently-live docs refer to, but the described syntax of the fold transform there does not match the schema: https://vega.github.io/vega/docs/transforms/fold/

[domoritz]

Here is the type in Typescript: https://github.com/vega/vega-typings/blob/e22ed3faa7dc7e9bba5607c249f526f98de23436/types/spec/transform.d.ts#L186

The type is a bit odd but not wrong. It says that we want an array with at least two items and the items should be strings. Any additional item should also be a string.

We can try to make the schema more strict.

[jakevdp]

Agree that it's technically correct but a bit odd.

What caught me off-guard is the use of an array of schemas for items. It's currently the only place in the vega-lite schema that that is used, and the fact that it led to such a strange schema made me wonder if the schema building tool was not handling it properly.

[jakevdp]

Maybe changing as?: [string, string]; to as?: string[]; would give a cleaner result?

Edit: or perhaps

  /**
   * An array of allowable step sizes to choose from.
   * @minItems 1
   */
  as?: string[]

This seems to work properly elsewhere in the typing specification.

[domoritz]

I'll look into it over at vega/ts-json-schema-generator#40.

[domoritz]

The typings now come from Vega-Typings and it would be nice to keep the strict TS typings.

[kanitw]

It says that we want an array with at least two items and the items should be strings. Any additional item should also be a string.

This is a bit inaccurate. The type there means there should b _strictly two items, and each of them should be a string.

[domoritz]

This is a bit inaccurate. The type there means there should b _strictly two items, and each of them should be a string.

The schema type is less strict and just says what I wrote. Your description is for the TS type.

[kanitw]

I see. Sounds like a bug that additionalItem is included.

[domoritz]

It's not wrong, just imprecise.

[domoritz]

Fixed in #4107

[jakevdp]

Thanks!