Initial implementation of FFI macro and codegen tool

[shadaj]

No description provided.

[Manishearth]

I actually don't think we should be doing this, because this adds an extra layer of indirection for the &self methods.

I'd do #[repr(transparent)] pub struct ICU4XFixedDecimal(pub FixedDecimal);and havenew()return aBox`

[Manishearth]

Aside from the Box thing, none of my suggestions are blocking, so we should be able to land this as a first pass if you'd like

[Manishearth]

suggestion (nb): I'd imagine that you want to collect the struct def too and store it alongside the methods (especially as we start having attributes on struct defs)

[Manishearth]

chore (nb): comments explaining what these fields are, especially this one

[Manishearth]

suggestion (nb): eventually should be a nestable enum

[Manishearth]

issue (nb): For experimentation it seems fair to directly do JS, but eventually we probably want the tool itself to just spit out JSON.

[Manishearth]

suggestion (nb): diplomat-core should probably export both:

• a way to get module+struct tree from a full syn crate
• a way to get a module+struct tree from a lib.rs root

[Manishearth]

Here's what the expanded code looks like so far!

$ cargo rustc -- -Zunpretty=expanded
   Compiling example v0.1.0 (/home/manishearth/dev/diplomat/example)
#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2018::*;
#[macro_use]
extern crate std;
mod ffi {
    use fixed_decimal::FixedDecimal;

    #[repr(transparent)]
    pub struct ICU4XFixedDecimal(pub FixedDecimal);

    impl ICU4XFixedDecimal {
        fn new(v: i32) -> Box<ICU4XFixedDecimal> {
            Box::new(ICU4XFixedDecimal(FixedDecimal::from(v)))
        }

        fn multiply_pow10(&mut self, power: i16) {
            self.0.multiply_pow10(power).unwrap();
        }

        fn digit_at(&self, magnitude: i16) -> u8 {
            self.0.digit_at(magnitude)
        }
    }
    #[no_mangle]
    pub extern "C" fn ICU4XFixedDecimal_new(v: i32)
     -> Box<ICU4XFixedDecimal> {
        ICU4XFixedDecimal::new(v)
    }
    #[no_mangle]
    pub extern "C" fn ICU4XFixedDecimal_multiply_pow10(this:
                                                           &mut ICU4XFixedDecimal,
                                                       power: i16) {
        this.multiply_pow10(power);
    }
    #[no_mangle]
    pub extern "C" fn ICU4XFixedDecimal_digit_at(this: &ICU4XFixedDecimal,
                                                 magnitude: i16) -> u8 {
        this.digit_at(magnitude)
    }
}

fn main() {
    let mut decimal = ffi::ICU4XFixedDecimal_new(123);
    ffi::ICU4XFixedDecimal_multiply_pow10(&mut decimal, -1);
}
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s

[Manishearth]

Ideally, for -> Box<Foo> we should have a different return type, and in the C code we should translate that to -> *mut Foo. But doesn't have to be done yet.

Anyway, this should be landable

[sffc]

Non-blocking review from me; feel free to merge once Manish's comments have been addressed!

(Also looking forward to when you can add documentation.)

[sffc]

Nit: I remember in our review of this earlier, you expressed intent to move the Box into the struct

[Manishearth]

Oh, I asked for it to be reversed: this makes reference semantics worse