fix: allow readonly arrays in interfaces

[LinusU]

Before this change, a readonly array would be inferred as "object":

interface TransactionInput {
  items: readonly { count: number, productId: string }[]
}

const transactionInputValidator = ajv.compile<TransactionInput>({
  additionalProperties: false,
  properties: {
    items: { type: 'array' }, // <--- Error: TS wants this to be "object"
  },
  required: ['items'],
  type: 'object'
})

Now this is properly inferred as "array".

---

What issue does this pull request resolve?

#1447

What changes did you make?

Changed T extends any[] to T extends readonly any[]. This works since readonly T[] is a subset of T[], and thus T[] always satisfies readonly T[].

Is there anything that requires more attention while reviewing?

The one word changed 😄

[epoberezkin]

that's because of the conditional fall-through to objects - at first I thought there is something more weird going on :)

Thank you!

[LinusU]

Thanks for the quick merge ❤️

When do you think this will be part of a release? I'm currently blocked on this 😅

[epoberezkin]

today then ;)

[epoberezkin]

https://github.com/ajv-validator/ajv/releases/tag/v7.1.1