[TypeScript] String enums allow incorrect widening

Description

swagger-codegen emits TypeScript enums in the form of:

export namespace Foo {
  export enum Bar {
    baz = <any> "baz",
    spam = <any> "spam"
  }
}

This is a hack to support string-based enums, since TypeScript's built-in support for enums only support numbers. However, this workaround is extremely dangerous, since it allows incorrectly widening the enum value to the number type even though it is a string:

const x: number = Foo.Bar.baz; // this compiles, even though it shouldn't
const y: string = Foo.Bar.baz; // this does not compile, even though it should

Swagger-codegen version

As late as 55443da

Swagger declaration file content or url

Any declaration file containing a string enum

Command line used for generation

Any swagger-codegen invocation that generates TypeScript

Suggest a Fix

According to a TypeScript dev, since TS 2.1, you can safely write string-based enums without the builtin enum keyword. This approach has minimal overhead and exploits keyof, lookup types, and type inference.

Read modules/swagger-codegen/src/main/resources/typescript-node/api.mustache and the linked TypeScript guidance first. Update the generated string-enum representation so its values remain string-typed rather than widening to number, then verify a generated declaration accepts string assignment and rejects number assignment.