typescript-definitions

Exports serde-serializable structs and enums to Typescript definitions.

Motivation

Now that rust 2018 has landed there is no question that people should be using rust to write server applications (what are you thinking!). But currently generating wasm from rust code to run in the browser is too bleeding edge. Since javascript will be dominant on the client for the forseeable future there remains the problem of communicating with your javascript from your rust server.

Fundamental to this is to keep the datatypes on either side of the connection (http/websocket) in sync.

Typescript is an incremental typing system for javascript that is as tricked as rust (almost!) so why not create a typescript definition library based on your rust code?

Please see Credits.

example:

extern crate serde_derive;
extern crate typescript_definitions;
extern crate wasm_bindgen;

use::wasm_bindgen::prelude::*;
use::serde_derive::Serialize;
use::typescript_definitions::TypescriptDefinition;

#[derive(Serialize, TypescriptDefinition)]
#[serde(tag = "tag", content = "fields")]
enum Enum {
    #[allow(unused)]
    V1 {
        #[serde(rename = "Foo")]
        foo: bool,
    },
    #[allow(unused)]
    V2 {
        #[serde(rename = "Bar")]
        bar: i64,
        #[serde(rename = "Baz")]
        baz: u64,
    },
    #[allow(unused)]
    V3 {
        #[serde(rename = "Quux")]
        quux: String,
    },
}

With wasm-bindgen this will output in your .d.ts definition file:

export type Enum = 
      {tag: "V1", fields: { Foo: boolean } }
    | {tag: "V2", fields: { Bar: number, Baz: number } }
    | {tag: "V3", fields: { Quux: string } }
    ;

Using `typescript-definitions`

NB: Please note these macros by default work only for the debug build since they pollute the code with strings and methods all of which are proabably not useful in any release (Since you are only using them to extract information about your current types from your code). In release builds they become no-ops. See features below if you want them in your release build.

In your crate create a lib target in Cargo.toml pointing to your "interfaces"

[lib]
name = "mywasm" # whatever... you decide
path = "src/interface.rs"
crate-type = ["cdylib"]


[dependencies]
typescript-definitions = "0.1.3"
wasm-bindgen = "0.2"
serde = "1"
serde_derive = "1"

Then you can run

cargo +nightly build --target wasm32-unknown-unknown
mkdir pkg
wasm-bindgen target/wasm32-unknown-unknown/debug/mywasm.wasm --typescript --out-dir pkg/
cat pkg/mywasm.d.ts

If you don't have these tools then see here:

rustup target add wasm32-unknown-unknown --toolchain nightly
cargo +nightly install wasm-bindgen-cli

or use wasm-pack (the typescript library will be in pkg/mywasm.d.ts)

curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
wasm-pack build
cat pkg/mywasm.d.ts

Using `type_script_ify`

You can ignore WASM totally and derive using TypeScriptify as long as you have the following TypeScriptifyTrait Trait in scope:

// interface.rs
extern crate serde_derive;
extern crate typescript_definitions;
// wasm_bindgen not needed
// use::wasm_bindgen::prelude::*;
use::serde_derive::Serialize;
use::typescript_definitions::TypeScriptify;
// *you* have to provide this Trait because, currently, rust proc-macro crates can't
// export any public Traits etc... sorry about that.
pub trait TypeScriptifyTrait {
    fn type_script_ify() -> &'static str;
}
#[derive(Serialize, TypeScriptify)]
pub struct MyStruct {
    v : i32,
}

Then in main.rs (say) you can generate your own typescript specification using Struct::type_script_ify():

mod interface;
// need to pull in trait
use self::interface::TypeScriptifyTrait;

fn main() {
    println!("{}", interface::MyStruct::type_script_ify());
    // prints "export type MyStruct = { v: number };"
}

Use the cfg macro To protect any use of type_script_ify()

if cfg!(any(debug_assertions, feature="export-typescript") {
    let s = A::type_script_ify();
}

If you have a generic struct such as:

#[derive(Serialize, TypeScriptify)]
pub struct Value<T> {
    value: T
}

Then you need to choose a concrete type: Value<i32>::type_script_ify(). The concrete type doesn't matter as long as it obeys rust; the output will still be generic export type Value<T> { value: T }.

Currently type bounds are discarded.

Features

There is an export-typescript feature to opt-in for release.

[dependencies.typescript-definitions]
version = "0.1.3"
features = ["export-typescript"]

## OR

typescript-definitions = { version="0.1.3",  features=["export-typescript"]  }

Serde Internally or Adjacently tagged Enums

See Serde Docs.

This crate understands #[serde(tag="type")] and #[serde(tag="tag", content="fields")] attributes but only for Struct variants.

It doesn't do Untagged or Externally tagged enums but defaults to #[serde(tag="kind")] (Internal).

The default for NewTypes and Tuple types is #[serde(tag="kind", content="fields")] (Adjacent).

Problems

Currently typescript-descriptions will not fail (AFAIK) even for structs and enums with function types Fn(A,B) -> C (generates C). These make no sense in the current context (data types, json serialization) so this might be considered a bug. Watchout!

This might change if use cases show that an error would be better.

The Option type is rendered as:

Option<T> => T | null

Serde always seems to render Result (in json) as {"Ok": T } | {"Err": E} i.e as "External" so we do too.

If you reference another type in a struct e.g.

    #[derive(Serialize)]
    struct B<T> {q: T}
    
    #[derive(Serialize, TypescriptDefinition)]
    struct A {
        x : f64, /* simple */
        b: B<f64>,
    }

then this will "work" (producing export type A = { x: number ,b: B<number> })) but B will be opaque to javascript unless B is also #[derive(TypescriptDefinition)].

Currently there is no help for this.

Formatting is rubbish and won't pass tslint. This is due to the quote! crate taking control of the output token stream. I don't know what it does with whitespace for example... (is whitespace a token in rust?). Anyhow this crate apply a few bandaid regex patches to pretty things up.

We are not as clever as serde in determining the actual type. For example this won't "work":

use std::borrow::Cow as Pig;

#[derive(TypeScriptify)]
struct S<'a> {
    pig: Pig<'a, str>,

gives export type S = { pig : Pig<string> } instead of export type S = { pig : string }

We can't reasonably obey serde attributes like "flatten" since we would need to find the actual Struct object (from somewhere) and query its fields.

TODO

Generate a typescript verifier for each type (maybe).

export verify_A<T>(obj: any) -> boolean

or something...

Then one could:

let o : any = JSON.parse(some_string_from_the_inet);
if verify_A<number>(o) {
    return obj as A<number>
} else {
    // err....
}

Credits

see http://timryan.org/2019/01/22/exporting-serde-types-to-typescript.html

Forked from wasm-typescript-definition by @tcr which was forked from rust-serde-schema by @srijs.

type_script_ify idea from typescriptify by @n3phtys

Probably some others...

License

MIT or Apache-2.0, at your option.

typescript-definitions 0.1.3