Use of `OneOf` type causing upcasting to `any`

[andyrichardson]

Description

The OneOf function hits a call stack limit on larger unions (>8 entities).

Name	Version
openapi-typescript	6.1.0
Node.js	19.1.0
Typescript	4.9.4
OS + version	macOS 13

Reproduction

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Expected result

OneOf type handles larger arguments without issue

Actual result

OneOf type exceeds call stack limit after an array of size 8.

Checklist

• I’m willing to open a PR (see CONTRIBUTING.md)

Notes

I've done the following as a workaround, although I suspect this will lead to type inaccuracies.

type OneOf<T extends any[]> = T[number];

[drwpow]

It seems the root issue here is the OneOf<…> type inference can only handle an array of n length before becoming too complicated to evaluate. It seems to be working fine for most small numbers (~ 5 or fewer). Will investigate a fix but it may be tricky to do so because it does matter quite a bit what is being evaluated.

[sebastian-fredriksson-bernholtz]

I'm not sure if it's worth the tradeoff, but I patched openapi-typescript to use union | instead of the OneOf generic type to handle this in a project of mine.

It seems like the cost of this issue might outweigh the value of being strict about excess properties.

[drwpow]

You raise a good point—if this isn’t working as-is, a union would give better results.

Funny enough the reason for the OneOf type came from anyOf requiring unions to work properly (it’s hard to believe but it’s true when you dig into how TS works). And the reasoning was if oneOf used unions too, it would functionally mean anyOf and oneOf generated the same TS types, which felt wrong on principle.

But that said, in practice, these are used very differently in schemas. And even if oneOf and anyOf generated the same TS types due to quirks of how the language works, it might produce the intended types better for both scenarios (since TS unions kinda handle both).

So anyways, I’ll investigate whether or not the OneOf helper is needed for most common cases; this library got by with unions for quite a while with no complaints.

[jonajames]

Crude and horrible workaround: pass a transform option to openapiTS that turns long oneOf into anyOf.

const transform = (schema, metadata) => {
  // Workaround for https://github.com/drwpow/openapi-typescript/issues/1019
  if ("oneOf" in schema && schema.oneOf.length > 5) {
    schema.anyOf = schema.oneOf
    delete schema.oneOf
  }
}