Custom error is ignored with multiply array items

[0pt1m1z3r]

Support plan

• is this issue currently blocking your project? (yes/no): yes
• is this issue affecting a production system? (yes/no): no

Context

• node version: 14.19.0
• module version with issue: 17.9.1, 17.9.2
• last module version without issue:
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...):
• any other relevant information:

What are you trying to achieve or the steps to reproduce?

Schema:

Joi.object({
    test: Joi.array().items(
        Joi.string(),
        Joi.number()
        .custom(function(value, helpers){
            if (value===5)
                return helpers.error('test_error');
            return value;
        })
        .messages({
            'test_error': 'Test error message',
        })
    ).single(),
})

Data To Validate:

{ 
  test: 5,
}

What was the result you got?

Validation Error: "test" does not match any of the allowed types

What result did you expect?

Validation Error: Test error message

[waggonerjake]

This is interesting. If you remove Joi.string(), you get the result you're looking for.

Joi.object({
  test: Joi.array()
    .items(
      Joi.number() //Removed Joi.string()
        .custom(function (value, helpers) {
          if (value === 5) return helpers.error('test_error');
          return value;
        })
        .messages({
          test_error: 'Test error message',
        }),
    )
    .single(),
});

//Returns 'Test error message'

If you instead return 6 instead of helpers.error('test_error'), it replaces it with 6 and passes validation.

Joi.object({
  test: Joi.array()
    .items(
      Joi.string(),
      Joi.number()
        .custom(function (value, helpers) {
          if (value === 5) return 6; //Replace error message with 6
          return value;
        })
        .messages({
          test_error: 'Test error message',
        }),
    )
    .single(),
});

//Passes validation, converts {test: 5} to {test: [6]}

[Marsup]

That's normal behavior, all possibilities will be attempted until a valid one is found, if none, there is no way to distinguish which one is the most likely, so this is the only rational error to provide.

[0pt1m1z3r]

@Marsup at least the second one has custom handler and it could have priority. Moreover I got the correct result by wrapping "items" to alternatives(). Why it's not a problem for alternatives() to distinguish it?

Joi.object({
    test: Joi.array().items(Joi.alternatives(
        Joi.string(),
        Joi.number()
        .custom(function(value, helpers){
            if (value===5)
                return helpers.error('test_error');
            return value;
        })
        .messages({
            'test_error': 'Test error message',
        })
    )).single(),
})