Cannot be used to index type error for generic conditional type

[pkudryashov]

Bug Report

🔎 Search Terms

Generic conditional type index

🕗 Version & Regression Information

• This is a regression
• This changed between versions 4.7.4 and 4.8.2

⏯ Playground Link

type Column<T = unknown> = (keyof T extends never ? { id?: number | string } : { id: T }) & {
    title?: string;
}

// no error if `key: keyof Column`
function getColumnProperty<T>(column: Column<T>, key: keyof Column<T>) {
    return column[key];
}

Output

"use strict";
// no error if `key: keyof Column`
function getColumnProperty(column, key) {
    return column[key];
}

Compiler Options

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "alwaysStrict": true,
    "esModuleInterop": true,
    "declaration": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "ES2017",
    "jsx": "react",
    "module": "ESNext",
    "moduleResolution": "node"
  }
}

Playground Link: Provided

🙁 Actual behavior

Error:" Type '"title" | keyof (keyof T extends never ? { id?: string | number | undefined; } : { id: T; })' cannot be used to index type '({ id?: string | number | undefined; } | { id: T; }) & { title?: string | undefined; }'.

🙂 Expected behavior

No error

[RyanCavanaugh]

Bisected to #49119

[RyanCavanaugh]

Let's track at the simpler repro at #50462