Symbols in const assertions should be considered unique

TypeScript Version: 3.8.0-dev.20191205

Search Terms:

• const assertion unique symbol
• "unique symbol" "as const"

Code

const prop = Symbol()
const dictionary = {
  prop: Symbol()
}
const sealedDictionary = {
  prop: Symbol()
} as const

class MyClass {
  // Works because "prop" is a unique symbol
  [prop]: 1

  // Does not work because "dictionary.prop" is not a unique symbol
  [dictionary.prop]: 2

  // Does not work because "sealedDictionary.prop" is not a unique symbol,
  // even though it probably should be?
  [sealedDictionary.prop]: 3
}

Expected behavior:

MyClass should probably accept sealedDictionary.prop as a computed property name since it should be considered a unique symbol.

Actual behavior:

TypeScript complains with TS1166:

A computed property name in a class property declaration must refer to an expression whose type is a literal type or a 'unique symbol' type.

Playground Link: Provided Updated (old link seems to be broken in new playground)

Related Issues: —

更新された TypeScript Playground の再現から始め、計算されたクラスプロパティ内の sealedDictionary.prop に対する TS1166 エラーを確認します。const assertions と unique symbol のプロパティ名に対する型チェックの経路を追跡し、sealedDictionary のケースが受け入れられ、拒否される dictionary のケースは変更されないことを示すカバレッジを追加します。