Generated *.d.ts files lose decorator information

[mendrik]

When writing a library that relies heavily on decorators in typescript, it would be beneficial if decorator information could be somehow preserved in the generated *.d.t.s file. I don't have any suggestion how it could be done except for maybe just code comments containing the original decorator.

Currently code like this

module feather.ui {

    import Construct = feather.annotations.Construct
    import Widget    = feather.core.Widget
    import deepValue = feather.objects.deepValue
    import TypedMap  = feather.types.TypedMap

    @Construct({selector: 'localization', singleton: true, attributes: ['translations']})
    export class Localization extends Widget {

        translations: TypedMap<any> = {}

        constructor(translations: TypedMap<any>) {
            super()
            this.translations = translations
        }

        translate = (key: string) =>
            deepValue(this.translations, key) || key
    }
}

could generate this:

declare module feather.ui {
    import Widget = feather.core.Widget;
    import TypedMap = feather.types.TypedMap;
    /* @Construct({selector: 'localization', singleton: true, attributes: ['translations']}) */
    class Localization extends Widget {
        translations: TypedMap<any>;
        constructor(translations: TypedMap<any>);
        translate: (key: string) => any;
    }
}

Since I'm writing a IDE plugin, I could read that comment to help me with looking up methods that satisfy particular criteria in a published library.

[mhegazy]

Decorators as they stand today have no impact on the type. they are more of an implementation detail if you may. thus keeping them in the declaration file is not correct. moreover, a decorator depends on expressions, e.g. @Construct( myVariable ) having that in your declaration file is a bit meaningless, since the value of myVariable is known only at runtime.

We do have a proposal for a design-time decorator, that acts more like comments in this case, and these would be trafficked to the generated .d.ts, see more in #2900

[mendrik]

thank you for your answer, I'll close this as you are right about the runtime aspect, which I didn't think through.