(feat) generate wasm-bindgen wrappers for #[rpc] methods in impl …

[ilijaljubicic]

Improvements

• Introduced #[rpc] attribute macro for impl blocks
• Automatically generates:
  • #[wasm_bindgen] struct with env: worker::Env
  • #[wasm_bindgen(constructor)] new(env: Env)
  • #[wasm_bindgen(js_name = "is_rpc")] method for JS discovery
• Replaces #[rpc] on methods with #[wasm_bindgen]
• Requires unique method names across all RPC exports
• Updated macro docs and runtime constraints

Allows using Env inside RPC methods. Open space for further improvements for the rpc functionality.

Related: #720

RPC methods can be exported using a custom #[rpc] attribute macro.
RPC methods must be defined inside an impl block annotated with #[rpc], and individual methods must also be marked with #[rpc].

When the macro is expanded, it generates:

• A #[wasm_bindgen]-annotated struct with env: worker::Env
• A constructor function: #[wasm_bindgen(constructor)] pub fn new(env: Env)
• A method #[wasm_bindgen(js_name = "__is_rpc__")] fn is_rpc(&self) -> bool for RPC auto-discovery
• All methods marked with #[rpc] converted into #[wasm_bindgen]-annotated exports

Example

#[rpc]
impl Rpc {
    #[rpc]
    pub async fn add(&self, a: u32, b: u32) -> u32 {
        // self.env available 
        a + b
    }
}

Expands to:

#[wasm_bindgen]
pub struct Rpc {
    env: worker::Env,
}

#[wasm_bindgen]
impl Rpc {
    #[wasm_bindgen(js_name = "__is_rpc__")]
    pub fn is_rpc(&self) -> bool {
        true
    }
    #[wasm_bindgen(constructor)]
    pub fn new(env: worker::Env) -> Self {
        Self { env }
    }

    #[wasm_bindgen]
    pub async fn add(&self, a: u32, b: u32) -> u32 {
        a + b
    }
}

Used in in rpc client workers:

export default {
  async fetch(request, env) {
    const result = await env.RPC_SERVICE.add(1,2);
    return new Response(JSON.stringify(result, null, 2));
  }
}