Idea: generate the TypeScript `.d.ts` definition files

[remorses]

Napigen already has all the Zig function and struct signatures which means it should be easy to add .d.ts files generation

This would make the generated .node module type safe

For example this code

const std = @import("std");
const napigen = @import("napigen");

export fn add(a: i32, b: i32) i32 {
    return a + b;
}

comptime {
    napigen.defineModule(initModule);
}

fn initModule(js: *napigen.JsContext, exports: napigen.napi_value) !napigen.napi_value {
    try js.setNamedProperty(exports, "add", try js.createFunction(add));

    return exports;
}

Would generate the following declartation:

export function add(a: number, b: number): number

[cztomsik]

Yes, this could be a great addition, but:

• It needs to generate .d.ts files, so it must be a build task (which isn’t as easy as comptime).
• It should probably parse doc comments too, adding some extra complexity.
• Not everything maps 1:1 from Zig to TypeScript, so to be truly useful (in practice), there should be some hooks or configurable customizations.

I’m not sure—if you want to do a proof of concept, I’m willing to take a look. But at this point, it’s not something I want to work on, at least not right now. I’m also not convinced about its real-world utility, since the JS↔native bridge usually remains a low-level building block (with limited scope) in the broader TS project. And if that bridge is 10-20 functions than any is not really that big issue, because everything else remains typed.