Bug Report

🔎 Search Terms

reduction, generic, union, intersection

🕗 Version & Regression Information

This bug is also the 'Nightly' version. Versions prior to 4.6.2 give even more errors.

⏯ Playground Link

Playground link with relevant code

💻 Code

type NumericLiteral = {
  value: number;
  type: "NumericLiteral";
};
type StringLiteral = {
  value: string;
  type: "StringLiteral";
};
type Identifier = {
  name: string;
  type: "Identifier";
};
type CallExpression = {
  name: string;
  arguments: DropbearNode[];
  type: "CallExpression";
};

type DropbearNode =
  | NumericLiteral
  | StringLiteral
  | Identifier
  | CallExpression;

type Visitor = {
  [K in DropbearNode["type"]]: (node: Extract<DropbearNode, { type: K }>) => void
};

function visitNode<K extends DropbearNode['type']>(node: Extract<DropbearNode, { type: K }>, v: Visitor) {
   v[node.type](node) // error
}

🙁 Actual behavior

typeof node.type is inferred as (K & "NumericLiteral") | (K & "StringLiteral") | (K & "Identifier") | (K & "CallExpression") that it is equal to K itself considering that K extends "NumericLiteral" | "StringLiteral" | "Identifier" | "CallExpression".
Something goes really wrong when I try to use node.type as an index, maybe because its type doesn't perform well if used as an index to access the Visitor type.

🙂 Expected behavior

typeof node.type inferred as K because it is simpler to interact with and doesn't give problems if used as an index.