Strict object schema with a boolean property expects alternative, not boolean

[joshkel]

Support plan

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

Context

• node version: 14.19.3
• module version with issue: 17.6.1
• last module version without issue: 17.6.0
• environment (e.g. node, browser, native): Node
• used with (e.g. hapi application, another framework, standalone, ...): Hapi
• any other relevant information: TypeScript 4.8.2

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

Joi 17.6.1's addition of AlternativesSchema for a strict object map has caused TypeScript to start reporting an error for boolean properties.

interface Test {
  enabled: boolean;
}

Joi.object<Test, true>({
  enabled: Joi.boolean(),
});

What was the result you got?

error TS2739: Type 'BooleanSchema' is missing the following properties from type 'AlternativesSchema': conditional, match, try

What result did you expect?

Successful compilation.

The problem appears to be that IsUnion returns true for booleans. I think that this may be because TypeScript treats boolean as the union of true and false (see the mentions of 'boolean' within checker.ts), but I'm really not sure. See also Stack Overflow's discussion on the limitations of an IsUnion implementation.

To fix it, maybe reorder ObjectPropertiesSchema to check boolean before union?

TypeScript playground link for experimenting with IsUnion implementations

(I'm not sure about ObjectPropertiesSchema's union check for another reason: It thinks that interface Test { value: 'a' | 'b' } should use an AlternativesSchema, but it seems like a more idiomatic Joi implementation would be Joi.string().valid('a', 'b'). That's a separate issue and not currently affecting me, but I wanted to mention it in case it affects how this issue should be addressed. Thanks!)

[matgott]

Same issue here.

[Marsup]

@matgott in general, please avoid doing that, "+1 comments" are not bringing new information nor helping projects prioritize issues. Use GitHub's 👍🏻 reaction if you want to vote for issues instead.

[Marsup]

@joshkel I've tried bringing it right after the boolean check, it then breaks the alternatives case, still looking into possible solutions but it seems tricky.

[Marsup]

@joshkel I think I've found a way that works for all cases (see #2850), can you check in your project if that causes other regressions elsewhere?

[wodCZ]

I'm getting into the same issue with union strings:

export interface ConfigSchema {
  NODE_ENV: 'development' | 'production' | 'test';
}


export const schema = Joi.object<ConfigSchema, true>({
  NODE_ENV: Joi.string()
    .valid('development', 'production', 'test')
    .default('production'),
// ^ TS2739: Type 'StringSchema' is missing the following properties from type 'AlternativesSchema': conditional, match, try
});

But maybe I'm using it wrong 🤷‍♂️ I didn't expect a breaking change in a patch release, so I can't dig deeper now.

[Marsup]

Your use case seems valid, maybe I'll revert that change until there's a reliable solution 🤔

[joshkel]

I have an attempted fix at #2851. I'm really not sure if this works for all cases and is the best approach, but it seems to cover both my booleans and the 'development' | 'production' | 'test' constant from @wodCZ.

[Marsup]

That was going to be my next attempt, thanks a lot, I think that works.

[Marsup]

New version is published.