Type argument inference fails using partial generic type when it should be possible

Bug Report

When trying to infer a type argument when the argument is used as a generic to another type which itself is nested inside Partial<...>, type inference fails.

🔎 Search Terms

type inference fail partial generic
type inference error partial generic

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about inference.

⏯ Playground Link

Playground link with relevant code

💻 Code

type Target = 'mongodb' | 'jsonSchema7' | 'openApi3'

interface NormalProps<TTarget extends Target> {
  target: TTarget
  normal: number
}

interface MongoProps {
  target: Extract<Target, 'mongodb'>
  mongo: number
}

type Props<TTarget extends Target = 'jsonSchema7'> = TTarget extends Exclude<Target, 'mongodb'>
  ? NormalProps<TTarget>
  : MongoProps;

const t = <TTarget extends Target = 'jsonSchema7'>(props: Partial<Props<TTarget>>) => {}

t({ target: 'openApi3' })

🙁 Actual behavior

Type inference fails, error is displayed: Type '"openApi3"' is not assignable to type '"jsonSchema7"'.. When manually passing the generic - t<'openApi3'>({ target: 'openApi3' }) - everything works fine.

🙂 Expected behavior

Type inference should be successful, as one of the discriminating properties (target) is set.

Start by reproducing the inference failure in the linked TypeScript Playground using the provided generic types and call, then compare it with the explicit t<'openApi3'> call. Investigate the compiler's type argument inference for the Partial<Props<TTarget>> parameter; done means the inferred call accepts target: 'openApi3' without an error while preserving the expected generic behavior.