[TypeScript] String enums allow incorrect widening

[kourge]

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.

[dartzki]

typescript 2.4 will support string enums: microsoft/TypeScript#15486

[xmeng1]

Why the typescript enum type generate with <any> which make it duplicate

export enum xxxTypeEnum {
        AAA = <any> 'AAA',
        BBBB = <any> 'BB_BB',
        CCC = <any> 'CCC'
    }

And when I use for (let obj in xxxTypeEnum), there will be 4 items, and the BBBB will be duplicated with BBBB and BB_BB.

Is there any reason to add this generic?
See this demo

[kourge]

With TypeScript 2.4, you should not need the <any> casts when writing a string enum. This gives you the correctly emitted object without duplicates.