Unable to compile const enum in .d.ts file.

[zheeeng]

I'm using .d.ts to store some enum interfaces. But it seems that ts-loader doesn't include these .d.ts files in compiling.

A work situation:

// foo.ts
const enum Direction {
    Up,
    Down,
    Left,
    Right,
}

const d: Direction = Direction.Up

output:

var d = 0 /* Up */;

For reusing Direction as value and interface, I separated declaration and its applying. Unfortunately, the compiling failed.

// foo.d.ts
declare const enum Direction {
    Up,
    Down,
    Left,
    Right,
}
// foo.ts
const d: Direction = Direction.Up

output:

var d = Direction.Up

This way report ReferenceError: Direction is not defined in webpack compliing result.

[KnisterPeter]

@zheeeng Couldn't you just export your const enum from 'foo.ts'?
Otherwise you may use a tripple-slash-directive to reference your 'foo.d.ts' which will instruct the compiler to include your file.

[zheeeng]

@KnisterPeter

const enum is handy for number semantic. declare is handy for using in global. The more important, typescript allow us to use them in that way.
export means we have to import it everywhere. And the behaviour difference between native typescript compiled and the transpiled brings a little inconvenience.

[KnisterPeter]

@zheeeng Fair engouth. Does it work with plain tsc? I doubt this is a ts-loader issue, since ts-loader just calls tsc from webpack (but I'm not sure, could be some side-effect).

[KnisterPeter]

I think you need to add a tripple-slash somewhere in your source like this:

/// <reference path="./foo.d.ts" />

This is a way to tell the tsc to include your declaration in your compilation.
As far as I know you can either use import/export or tripple-slash references to include files in your compiler context.

[zheeeng]

@KnisterPeter tsc works fine. I think it is something caused by webpack only consider files things are imported. Declaration files don't need to be imported.
If it is the reason. I doubt tripple-slash import works.
Certainly, webpack won't take this issue. Maybe some improvements on ts-loader will help.

[KnisterPeter]

@zheeeng Please add a minimal repository to test this issue. It may help to understand it a bit more.

[zheeeng]

Ok, I try build one.

[zheeeng]

@KnisterPeter very sorry for my mistakes. I just then build a minimal project for test, if the declaration file is included by 'include' option tsconfig.json. It indeed is transpiled right.
The issue was created when I was developing project with complicated configs, VS Code didn't report error while the const enum declaration is out of the include range that be defined by tsconfig.json.

[KnisterPeter]

Your welcome. I'm glad to help.

[jestarray]

Having this issue currently with the Vue CLI that uses webpack and ts-loader under the scenes.

vuejs/vue-cli#3376

tried flipping transpileOnly on and off, and happymodepack on and off, no luck.

[navneet-g]

Is there a way to generate a build error when we use enum instead of const enum in d.ts files?