🐝 typescript-inference-problem

Demonstration a type inference problem in TSServer.

Usage

npm ci
npm start # node_modules/.bin/tsserver < commands.json

Source

interface Params {
  foo: string | undefined;
}

export default (params: Params) => params.foo;
//     ^---- quickinfo here

Expected

// ...(omitted)
"displayString": "(property) default: (params: Params) => string | undefined"
// ...(omitted)

Got

// ...(omitted)
"displayString": "(property) default: (params: Params) => string"
// ...(omitted)