Add support for computed properties

[TrevorSayre]

type Letters = 'a' | 'b' | 'c' | 'd' | 'e';
type Numbers = 1 | 2 | 3;
type Chars = '$' | '_';

type Names = `${Letters}${Uppercase<Letters>}${Numbers}${Chars}`;

// Quick fix available
// so computed properties, transforms, and long lists work
const names: { [K in Names]: K } = {};

type Letters = 'a' | 'b' | 'c' | 'd' | 'e';
type Numbers = 1 | 2 | 3;
type Chars = '@' | '!'; // Difference is only this line

type Names = `${Letters}${Uppercase<Letters>}${Numbers}${Chars}`;

// Quick not available
const names: { [K in Names]: K } = {};

The last example works in WebStorm via "implement all members" and would be a welcome addition to VSCode. The quick fix for microsoft/TypeScript#28491 was implemented via microsoft/TypeScript#44576 and solved some use cases, but not this one.

The error output does already suggest all the missing properties. It seems like the data is available to execute a quick fix.

Such names should be usable:

Additionally, when the quick fix does work, it only adds the properties and sets values as undefined even when the value is known (as in the above examples).

This issue was inspired by this tweet:
https://twitter.com/majidrazvi/status/1449493443743391746

[tamj0rd2]

@TrevorSayre What's the expected outcome here? I suppose you'd want it to be populated with all of the different combinations?

[TrevorSayre]

@TrevorSayre What's the expected outcome here? I suppose you'd want it to be populated with all of the different combinations?

That's correct. Ideally both the indicated property names and values (when known) instead of the current undefined value. The working examples show this.

[TrevorSayre]

Updated the issue description for further clarity.

[tamj0rd2]

Thanks for updating with those details! I'll try to get around to it in the next couple of weeks. I'm not working with Typescript much anymore, so any contributions are welcome.