⚙️ layer-tl-gen

Build-time Rust code generator for Telegram's TL schema.

From TL AST to idiomatic Rust structs, enums, and traits — automatically.

📦 Installation

[build-dependencies]
layer-tl-gen = "0.4.6"

This crate is a build-dependency only. It runs during cargo build via build.rs and produces Rust source code. It is not linked into your final binary.

✨ What It Does

layer-tl-gen takes a parsed TL AST (from layer-tl-parser) and generates complete, idiomatic Rust source code — structs for constructors, enums for abstract types, and trait implementations for functions.

It runs at build time via build.rs, so the generated code is always in sync with the schema — no manual updates needed. Regeneration is automatic whenever the .tl file changes (via cargo:rerun-if-changed).

🏗️ What Gets Generated

For every TL definition in the schema, layer-tl-gen produces three categories of output:

1. Constructor → Rust struct + ser/de

peerUser#9db1bc6d user_id:long = Peer;

// in mod types
pub struct PeerUser {
    pub user_id: i64,
}
impl Serializable   for PeerUser { /* TL wire encoding */ }
impl Deserializable for PeerUser { /* TL wire decoding */ }

2. Abstract type → Rust enum + discriminated deserialization

peerUser    = Peer;
peerChat    = Peer;
peerChannel = Peer;

// in mod enums
pub enum Peer {
    User(PeerUser),
    Chat(PeerChat),
    Channel(PeerChannel),
}
// Deserializable dispatches on the 4-byte CRC32 constructor ID
impl Deserializable for Peer { ... }

3. Function → struct + RemoteCall impl

messages.sendMessage#545cd15a peer:InputPeer message:string random_id:long = Updates;

// in mod functions::messages
pub struct SendMessage {
    pub peer:      enums::InputPeer,
    pub message:   String,
    pub random_id: i64,
    // ... all fields from the schema
}
impl RemoteCall for SendMessage {
    type Return = enums::Updates;   // zero-cost type-level encoding of the return type
}
impl Serializable for SendMessage { ... }

4. Optional derives and conversions

Depending on the Config flags passed to generate():

// impl_debug = true
#[derive(Debug)]
pub struct PeerUser { ... }

// impl_from_type = true
impl From<types::PeerUser> for enums::Peer {
    fn from(v: types::PeerUser) -> Self { Self::User(v) }
}

// impl_from_enum = true
impl TryFrom<enums::Peer> for types::PeerUser {
    type Error = enums::Peer;
    fn try_from(v: enums::Peer) -> Result<Self, Self::Error> { ... }
}

// name_for_id = true
pub fn name_for_id(id: u32) -> Option<&'static str> { ... }

💡 Usage in build.rs

// layer-tl-types/build.rs
use layer_tl_gen::{generate, Config};

fn main() {
    let out_dir = std::env::var("OUT_DIR").unwrap();

    generate(
        "tl/api.tl",
        &format!("{out_dir}/generated_api.rs"),
        Config {
            impl_debug:      true,
            impl_from_type:  true,
            impl_from_enum:  true,
            impl_serde:      false,
            name_for_id:     false,
        },
    ).expect("TL code generation failed");

    // Tell Cargo to re-run if the schema changes
    println!("cargo:rerun-if-changed=tl/api.tl");
}

Then in your lib.rs or generated.rs:

// include the generated file
include!(concat!(env!("OUT_DIR"), "/generated_api.rs"));

⚙️ Config Options

pub struct Config {
    /// Generate `#[derive(Debug)]` on all types.
    pub impl_debug: bool,

    /// Generate `From<types::T> for enums::E` for all constructors.
    pub impl_from_type: bool,

    /// Generate `TryFrom<enums::E> for types::T` for all constructors.
    pub impl_from_enum: bool,

    /// Generate `serde::Serialize` / `Deserialize` on all types.
    /// Requires the `serde` crate to be available in the consuming crate.
    pub impl_serde: bool,

    /// Generate `name_for_id(u32) -> Option<&'static str>` lookup.
    /// Maps a constructor's CRC32 ID back to its TL name — useful for debugging.
    pub name_for_id: bool,
}

🧩 Module Layout of Generated Code

generated.rs
├── mod types      — one struct per TL constructor
├── mod enums      — one enum per TL abstract type
└── mod functions
    ├── mod account
    ├── mod auth
    ├── mod channels
    ├── mod contacts
    ├── mod messages
    ├── mod payments
    ├── mod phone
    ├── mod photos
    ├── mod stickers
    ├── mod stories
    ├── mod updates
    └── mod users

Each functions::* module mirrors the namespace prefix from the TL schema (messages.sendMessage → functions::messages::SendMessage).

🔗 Part of the layer stack

layer-tl-types  (consumes the generated code)
└── layer-tl-gen    ← you are here  (generates at build time)
    └── layer-tl-parser (parses the .tl schema)

📄 License

Licensed under either of, at your option:

• MIT License — see LICENSE-MIT
• Apache License, Version 2.0 — see LICENSE-APACHE

👤 Author

Ankit Chaubey
github.com/ankit-chaubey · ankitchaubey.in · ankitchaubey.dev@gmail.com

📦 github.com/ankit-chaubey/layer