# typescript-definitions
> Exports serde-serializable structs and enums to Typescript definitions.
[](https://crates.io/crates/typescript-definitions)
[](https://docs.rs/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 generating wasm from rust code to run in the browser is currently much 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 almost(!) as tricked as rust... so
why not create a typescript definition library based on your rust code?
Please see [Credits](#credits).
`typescript-definitions` (as of 0.1.7) uses `edition=2018` (heh).
example:
```rust
use::wasm_bindgen::prelude::*;
use::serde_derive::Serialize;
use::typescript_definitions::TypescriptDefinition;
#[derive(Serialize, TypescriptDefinition)]
#[serde(tag = "tag", content = "fields")]
enum Enum {
V1 {
#[serde(rename = "Foo")]
foo: bool,
},
V2 {
#[serde(rename = "Bar")]
bar: i64,
#[serde(rename = "Baz")]
baz: u64,
},
V3 {
#[serde(rename = "Quux")]
quux: String,
},
#[serde(skip)]
Internal {
err: String
},
}
```
Using [wasm-bindgen](https://rustwasm.github.io/wasm-bindgen/) this will output in your `*.d.ts` definition file:
```typescript
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. This means that there is *no cost* to your release exes/libs
or to your users by using these macros. Zero cost abstraction indeed. Beautiful.
Also, although you need nightly to run `wasm-bingen` *your* code can remain stable.
See [features](#features) below if you really want them in your release build.
There is a very small example in the repository that [works for me (TM)](https://bitbucket.org/athaliana/typescript-definitions/src/master/example/) if you want to get started
on your own.
This crate only exports two derive macros: `TypescriptDefinition` and `TypeScriptify`, a simple
trait `TypeScriptifyTrait` and a (very simple) serializer for byte arrays.
In your crate create a lib target in `Cargo.toml` pointing
to your "interfaces"
```toml
[lib]
name = "mywasm" # whatever... you decide
path = "src/interface.rs"
crate-type = ["cdylib"]
[dependencies]
typescript-definitions = "0.1"
wasm-bindgen = "0.2"
serde = "1"
serde_derive = "1"
```
Then you can run (see [here](#using-type_script_ify) if you don't want to go near WASM):
```bash
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 # here are your definitions
```
If you don't have these tools then [see here](https://rustwasm.github.io/wasm-bindgen/whirlwind-tour/basic-usage.html)
(You might also need to get [rustup](https://rustup.rs) first):
```bash
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`). (**NB** as of 1.0.7 this no longer seems to work)
```bash
cat pkg/mywasm.d.ts
```
## Using `type_script_ify`
You can ignore WASM *totally* by deriving using `TypeScriptify`:
```rust
// interface.rs
// wasm_bindgen not needed
// use::wasm_bindgen::prelude::*;
use::serde_derive::Serialize;
use::typescript_definitions::TypeScriptify;
}
#[derive(Serialize, TypeScriptify)]
pub struct MyStruct {
v : i32,
}
```
Then in `main.rs` (say) you can generate your own typescript specification using `MyStruct::type_script_ify()`:
```rust
mod interface;
// need to pull in trait
use typescript_definitions::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()`
```rust
if cfg!(any(debug_assertions, feature="export-typescript") {
let s = A::type_script_ify();
}
```
If you have a generic struct such as:
```rust
#[derive(Serialize, TypeScriptify)]
pub struct Value<T> {
value: T
}
```
then you need to choose a concrete type to generate the typescript: `Value<i32>::type_script_ify()`. The concrete type
doesn't matter as long as it obeys rust restrictions; the output will still be generic `export type Value<T> { value: T }`.
Currently type bounds are discarded in the typescript.
So basically with `TypeScriptify` *you* have to create some binary that, via `println!` or similar statements, will
cough up a typescript library file. I guess you have more control here... at the expense of complicating
your `Cargo.toml` file and your code.
### Features
As we said before `typescript-descriptions` macros pollute your code with
static strings and other garbage. Hence, by default, they only *work* in debug mode.
If you actually want `T::type_script_ify()` (for TypeScriptify) available in your
release code then change your `Cargo.toml` file to:
```toml
[dependencies.typescript-definitions]
version = "0.1"
features = ["export-typescript"]
## OR
typescript-definitions = { version="0.1", features=["export-typescript"] }
```
AFAIK the strings generated by TypescriptDescription don't survive the invocation
of `wasm-bindgen` even in debug mode. So your *.wasm files are clean. You still need
to add `--features=export-typescript` to generate anything in release mode though.
## Serde Internally or Adjacently tagged Enums
See Serde [Docs](https://serde.rs/enum-representations.html#internally-tagged).
`typescript-definitions` tries to adhere to the meaning of serde attributes
like`#[serde(tag="type")]` and `#[serde(tag="tag", content="fields")]`.
Before 0.1.8 we had an implicit default tag of "kind" for enums. Now we don't
(although we still have a implicit `transparent` on NewTypes).
Serde attributes understood
* rename, rename_all:
* tag:
* content:
* skip: (`typescript-definitions` also skips - by default - PhantomData fields ... sorry ghost who walks)
* serialize_with="typescript_definitions::as_byte_string"
* transparent: Newtypes are automatically transparent. Structs with a single field can
be marked transparent.
`serialize_with`, if placed on a `[u8]` or `Vec<u8>` field, will take
that field to be a string. (And serde_json will output a `\xdd` encoded
string of the array. *or* you can create your own... just ensure to name it `as_byte_string`)
Serde attributes understood but rejected
* flatten (This will produce a panic). Currently on my TODO list.
All others are just ignored.
## Problems
Oh yes there are problems...
Currently `typescript-descriptions` will not fail (AFAIK) even for
structs and enums with function pointers `fn(a:A, b: B) -> C` (generates typescript lambda `(a:A, b:B) => C`)
and closures `Fn(A,B) -> C` (generates `(A,B) => 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.
If you reference another type in a struct e.g.
```rust
#[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
typescript unless B is *also* `#[derive(TypescriptDefinition)]`.
Currently there is no check for this omission.
Also Trait bounds are stripped out for typescript; you can't serialize Traits! However...
If using `type_script_ify` then anything other than simple trait bounds will fail to compile. (because
the `impl<...> TypeScriptify for T<...> {}` that is automatically generated by `typescript-descriptions` will be garbled).
* no `where` clauses.
* no generic Traits.
Use `WASM` instead.
This might be relaxed in future.
----
The following types are rendered as:
* `Option<T>` => `T | null` (can't use undefined because this will mess with object checking)
* `HashMap<K,V>` => `{ [key:K]:V }` (same for `BTreeMap`)
* `HashSet<V>` => `V[]` (same for `BTreeSet`)
* `&[u8]` and `Vec<u8>` are expected to be byte buffers but are still rendered as `number[]` since
this is what `serde_json` does. However you can force the output to be a string using
`#[serde(serialize_with="typescript_defintions::as_byte_string")]`
An `enum` that is all Unit types such as
```rust
enum Color {
Red,
Green,
Blue
}
```
is rendered as a typescript enum:
```typescript
enum Color {
Red = "Red",
Green ="Green",
Blue = "Blue"
}
```
because serde_json will render `Color::Red` as the string `"Red"` instead of `Color.Red`
(because JSON).
Serde always seems to render `Result` (in json) as `{"Ok": T } | {"Err": E}` i.e as "External"
so we do too.
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 applies a few bandaid regex patches to pretty things up.
We are not as clever as serde or the compiler in determining the actual type. For example this won't "work":
```rust
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 }`
At a certain point `typescript-definitions` just *assumes* that the token identifier `i32` (say)
*is* really the rust signed 32 bit integer and not some crazy renamed struct in your code!
Complex paths are ignored `std::borrow::Cow` and `mycrate::mod::Cow` are the same to us. We're
not going to reimplement the compiler to find out if they are *actually* different. A Cow is
always "Clone on write".
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). We really need some
testing of the typescript types against serde_json.
```typescript
export verify_A<T>(obj: any): boolean {/*... */ }
// *or*
export verify_A<T>(obj: any): {Ok: A<T>} | {Err: string} {/* ... */}
// *or* using guards https://www.typescriptlang.org/docs/handbook/advanced-types.html
export is_A<T>(obj: any): obj is A<T> { /* ... */ }
```
or something...
Then one could:
```typescript
let o : any = JSON.parse(some_string_from_the_inet);
if verify_A<number>(o) {
return o as A<number>
} else {
// err....
}
```
maybe...
## Credits
For intial inspiration see http://timryan.org/2019/01/22/exporting-serde-types-to-typescript.html
Forked from [`wasm-typescript-definition` by @tcr](https://github.com/tcr/wasm-typescript-definition?files=1)
which was forked from [`rust-serde-schema` by @srijs](https://github.com/srijs/rust-serde-schema?files=1).
`type_script_ify` idea from [`typescriptify` by @n3phtys](https://github.com/n3phtys/typescriptify)
Probably some others...
## License
MIT or Apache-2.0, at your option.