Private methods in d.ts files should be declared with rest parameters to make them more stable

[dbaeumer]

TypeScript Version: 1.8.0 / nightly (2.0.0-dev.201xxxxx)

Code

export class Bug {
    private method(one: number, two: string): string {
    }
}

To make the d.ts more stable I think that the generated d.ts file should look like this:

export declare class Bug {
   private method(...params); 
}

Since the actual number of params of that method doesn't matter. All that is need is the name. This keeps the shape of a TS module more stable if private members change.

[yahiko00]

I am just wondering why the generated declaration file .d.ts even contains private members.

[RyanCavanaugh]

@yahiko00 see #1867

@dbaeumer I don't see what the endgoal of "stability" is here. Why does it matter at all? People are going to be confused about why it's declared with a different arity than it was written with.

[yahiko00]

@RyanCavanaugh Ok I understand the purpose of letting private members in d.ts files for avoiding some weird bugs.

[dbaeumer]

@RyanCavanaugh we use d.ts file to compute the impact of upwards compilation between modules. If the 'public' shape of a module doesn't change the modules that depend on it don't need to be recompiled. According to the discussion in #1867 names of private members belong to the public shape however not its full signature. Rest params allow to only put the minimal necessary information into the shape to achieve this.

[dbaeumer]

A builder that would profit from this can be found here: https://github.com/Microsoft/TypeScript/tree/dbaeumer/9125

[RyanCavanaugh]

Why doesn't your difference-computer simply ignore the types of private members? That's going to be a more comprehensive fix, especially because e.g. changing something from a method to an arrow function is going to show up as a difference.

[mhegazy]

i agree with @RyanCavanaugh, the fix here is not to change the .d.ts emit output, but rather to optimize the public API shape differ. today it uses the .d.ts output, but there is no reason it can not be a separate output.

[dbaeumer]

OK. I take the point of making the differ of the shape aware of this. But why does a private signature list the param names in the first place. The only reason why the private member is in is to check for overriding the name. Adding the param names is not necessary and only leaks unnecessary information into the d.t.s file.

[kitsonk]

Like it or not, private isn't private at runtime. I would expect a d.ts file to properly represent the logical constructs in typescript, which would include the full definition of a method, because essentially it is only private by convention. While it maybe providing typing information for the parameters, it certainly isn't leaking anything that isn't already in the runtime emit.

[dbaeumer]

I understand that private isn't private at runtime. This is exactly the reasoning behind my argument. I want to make it hard for other to call my private members. The more information we leak into a d.ts the easier it is.

[RyanCavanaugh]

I think they have your code anyway? 😕

[dbaeumer]

So what is the reasoning behind putting the whole signature if not necessary.

[DanielRosenwasser]

Not to go off topic, but how come we even display the method signature at all? For private properties we just display any.

[kitsonk]

Not to go off topic, but how come we even display the method signature at all? For private properties we just display any.

Personal opinion (as they all are) that isn't "lying", where as changing the arity of a method would be. Stripping all the type information might be logical:

export declare class Bug {
    private method(one: any, two: any): any;
}

That represents what is actually in the code without any additional information.

[dbaeumer]

This is already the case. The d.t.s looks like this:

export declare class Bug {
    private method(one, two);
}

which is implicit any.

[RyanCavanaugh]

Accepting PRs to just emit

class Bug {
  method;
}

[Igorbek]

Since the effort is easy I grabbed it and made a PR #11030