Combine type error messages

[jdesrosiers]

Currently, if you have multiple type keywords apply to a single location, you'll get multiple error messages. For example,

{
  "allOf": [
    { "type": ["string", "boolean", "number"] },
    { "type": ["string", "number"] },
    { "type": "string" }
  ]
}

The user will get,

• Expected a string, boolean, or number
• Expected a string or number
• Expected a string

This is mostly noise for the user. All they need to see is,

• Expected a string

This task is to update the type error handler to collapse all type errors into a single message.

[srivastava-diya]

My understanding

Instead of emitting multiple type errors, we can normalize each type into a set and compute their intersection. The final expected type set represents the actual constraint on the instance and should be used as a single error message.

Please let me know if I can be assigned. Thanks.