change error.field -> rule.field

[iwillwen]

Actually when we have to do some i18n process on the error message, we have to inject the proper field name into the message but not the field name in code (such as password VS 密码).
In async-validator developer can assign the correct field name with the fullField rule property, but when the field validation is failed the error return should contain the original field name that we can use it to do some other things what it is not do now.

[coveralls]

Coverage remained the same at 88.095% when pulling dfe30bb on iwillwen:master into 3bb6943 on yiminghe:master.

[iwillwen]

Example:

const validator = new Schema({
  password: { type: 'string', required: true, min: 6, max: 20, fullField: '密码' }
})
validator.validate({ password: 123456 }, (errors, fields) => {
  console.log(fields.password)  //=> undefined
  console.log(fields['密码'])    //=> correct, but WTF?
})

[yiminghe]

No, you can not use fullField, it's not a api, only for internal usage, use message for i18n

[iwillwen]

@yiminghe
Thanks for your response. Actually I knew the fullField is a private variable, but I did not find any way to define a method or a callback function for transforming the field name into the correct format or correct language I want in the source code.
The messages part in async-validator just only allow me to define a regular string format to receive the original field name.
For example, if thepassword field is required so that I want async-validator feedback the message like 密码必填, but not password 必填.
There are two solution to solve the issue.

1. message could be a function, so that it could be defined by the developers to make the error message just like they want.

validator.messages({
  required: rule => `${i18n(rule.field)}必填`
})

2. the message of every single rules could be assigned.

new Schema({
  password: {
    type: 'string',
    required: {
      enabled: true,
      message: '密码必填'
    }
  }
})

Or

new Schema({
  password: {
    type: 'string',
    required: true,
    messages: {
      required: '密码必填'
    }
  }
})

[yiminghe]

I agree with functional message. Welcome pr.

[elvuel]

@yiminghe how about add a LocalizedField to RuleItem? for instance ValidateMessage<[LocalizedField | FullField, ...]> , preserve the default internal validation messages.