Preserve radix when pretty-printing numeric literal types

Suggestion

🔍 Search Terms

numeric literal radix, non-decimal numeric literal types

List of keywords you searched for before creating this issue. Write them down here so that others can find this suggestion more easily and help provide feedback.

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn’t be a breaking change in existing TypeScript/JavaScript code
• This wouldn’t change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn’t a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript’s Design Goals.

⭐ Suggestion

If a numeric literal type was defined explicitly with a non-decimal literal, it should be displayed as such in editor hovers and other places where it is pretty-printed.

📃 Motivating Example

Often, non-decimal literals are more-or-less self-documenting in a context:

declare const MASK: 0b1011; // it is obvious which bits are set
// vs
declare const MASK: 11; // wat?

declare const PERMISSIONS: 0o777; // unix file system permissions
// vs
declare const PERMISSIONS: 511; // wat?

declare const ARGB: 0x00ffff00; // yellow pixel color
// vs
declare const ARGB: 16776960; // wat?

declare const ASCII_CODE: 0x1b; // ASCII code for backspace
// vs
declare const ASCII_CODE: 27; // wat?

Ideally, the radix should carry over to the “autoincremented” enum members:

enum AsciiLetters {
  A = 0x61, B, C, D, E, F,  /* ... */, Z,
}
// AsciiLetters.E: 0x65

💻 Use Cases

Bit masks. Unix file system permissions. RGB colors. Hexadecimal ASCII/Unicode code points.

[Kingwl]

It’s might be a breaking change. Might should behind a flag?

[iliazeus]

I am concerned about declaration emit, for the same reasons I described above.

Funnily enough, when I test it on the playground, JS emit preserves the radix, but not the .D.TS emit:

https://www.typescriptlang.org/play?ts=4.4.0-beta#code/KYDwDg9gTgLgBAYwgOwM7wLIHkAiBROAXjgAYIB2SgbgFgAoIA