Unable to infer function input type from previous element in nested tuple

[ssalbdivad]

Bug Report

🔎 Search Terms

tuples, inference, functions, parameters, parsing, arktype, mapped types

🕗 Version & Regression Information

• This is the behavior in every version I tried (tested up to nightly)

⏯ Playground Link

Playground link with relevant code

💻 Code

type MorphTuple = [string, "|>", any]

type validateMorph<def extends MorphTuple> = def[1] extends "|>"
    ? [validateDefinition<def[0]>, "|>", (In: def[0]) => unknown]
    : def

type validateDefinition<def> = def extends MorphTuple
    ? validateMorph<def>
    : {
          [k in keyof def]: validateDefinition<def[k]>
      }

declare function type<def>(def: validateDefinition<def>): def

// Function input (x) inferred as "ark"
const shallow = type(["ark", "|>", (x) => x.length])
const objectLiteral = type({ a: ["ark", "|>", (x) => x.length] })

// Function input inferred as any (should be "ark")
const nestedTuple = type([["ark", "|>", (x) => x.length]])

🖊️ Description

I encountered this bug a few months ago and originally logged an issue within ArkType, but suspected it was a TS bug given the inconsistency in the behavior particularly between the object literal and tuple cases.

The goal of this minimal repro is to narrow the function's input definition and use the type of the first element to infer the input parameter for the third element's function type.