TS: Class fields that use declare cannot be initialized

[marvinhagemeister]

Came across this pattern in the wild which throws an error with esbuild but passes compilation with tsc:

declare const isOptional: unique symbol;

class Foo {
  public declare readonly [isOptional] = true;
}

// TSC detects "a" as being true
const a = new Foo()[isOptional]

The error thrown by esbuild:

✘ [ERROR] Class fields that use "declare" cannot be initialized

    src/parser/v2/test2.ts:4:42:
      4 │   public declare readonly [isOptional] = true;

[evanw]

Huh weird, TIL. It looks like this is a very narrow special case (you can't even set it to null). I'll just allow anything here and let the type checker enforce the special cases.