Don't show string literals as completion options for string enums

[rokoroku]

TypeScript Version: 2.4.1

Code

const enum StringEnumType {
  STATUS_PENDING = 'PENDING',
  STATUS_COMPLETED = 'COMPLETED',
}

function aFunction(type: StringEnumType) { /* ... */ }

aFunction(StringEnumType.STATUS_PENDING); // OK
aFunction('PENDING');  // Error:  [ts] 'Argument of type '"PENDING"' is not assignable to parameter of type 'StringEnumType'.

Expected behavior:

• No error or no suggestion.

Actual behavior:

• TS's suggestion shows the string values of the enums, but we cannot use the string values as it is.

 [ts] 'Argument of type '"PENDING"' is not assignable to parameter of type 'StringEnumType'.