Enum keys not accepted as computed properties if their name is not a valid identifier

TypeScript Version: 2.9.2

Search Terms: computed property name

Code

enum Type {
  Foo = 'foo',
  '3x14' = '3x14'
}

type TypeMap = {
  [Type.Foo]: any
  [Type['3x14']]: any
}

Expected behavior:
Type['3x14'] to be usable as a computed key in a type definition.

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

This is the case even for Type.Foo if it's written as Type['Foo'] instead; so it seems there is some early bailout when the bracket operator is involved. For certain key names it may not be possible to write them without resorting to brackets, like a name that starts with a digit.

Playground Link: Link

Reproduce the TypeScript 2.9.2 example in the linked Playground, then compare the accepted [Type.Foo] form with the rejected [Type['3x14']] form. Trace computed property name checking for enum member access and confirm that bracket access to a non-identifier enum member is accepted as a literal type.