derive-defs

Declarative derive preset configuration via TOML with proc-macro generation.

Overview

derive-defs allows you to define named sets of derive attributes through a declarative TOML configuration. This is useful when you have common derive patterns that you use repeatedly across your codebase.

Why not macro_rules_attribute?

Existing solutions require defining aliases directly in code. derive-defs offers:

• External Configuration: Define presets in TOML, not code
• Inheritance: Bundles can extend other bundles via extends
• Cross-file Imports: Split configuration across multiple files
• Runtime Modification: Use omit/add to modify bundles at use site

Quick Start

1. Create derive_defs.toml

[defs.serialization]
traits = ["Clone", "Serialize", "Deserialize"]
attrs = ['#[serde(rename_all = "camelCase")]']

[defs.model]
traits = ["Debug", "Clone", "PartialEq"]

[defs.entity]
extends = "model"
traits = ["Serialize", "Deserialize"]
attrs = ['#[serde(rename_all = "camelCase")]']

2. Set up build.rs

fn main() {
    derive_defs::generate("derive_defs.toml")
        .expect("Failed to generate derive defs");
}

Add to Cargo.toml:

[build-dependencies]
derive-defs = "0.1"

3. Use in your code

use my_crate_macros::*;

#[serialization]
struct User {
    name: String,
    age: u32,
}

// Modify at use site
#[serialization(omit(Clone), add(Default))]
struct Config {
    host: String,
}

TOML Configuration

Basic Syntax

[defs.<name>]
traits = ["Trait1", "Trait2"]  # List of derive traits
attrs = ["#[attr]"]             # Additional attributes
extends = "<parent>"            # Inheritance (optional)

Inheritance (extends)

[defs.base]
traits = ["Debug", "Clone"]

[defs.value_object]
extends = "base"
traits = ["PartialEq", "Eq", "Hash"]
# Result: Debug, Clone, PartialEq, Eq, Hash

Cross-file Imports (includes)

[includes]
common = "shared/common_defs.toml"

[defs.api_response]
extends = "common.serialization"
traits = ["Default"]

API Usage

Attribute Modifiers

// Basic usage
#[serialization]
struct User { }

// Exclude Clone from the bundle
#[serialization(omit(Clone))]
struct Session { }

// Add Default and Hash to the bundle
#[serialization(add(Default, Hash))]
struct Config { }

// Exclude serde attributes
#[serialization(omit_attrs(serde))]
struct Internal { }

// Combination
#[serialization(omit(Clone), add(Copy))]
struct Flags { }

Error Handling

The crate provides clear error messages at build.rs time:

• Circular inheritance: error: circular extends detected: a → b → c → a
• Undefined parent: error: def "child" extends "parent" which is not defined
• Missing include: error: include file "common.toml" not found
• Duplicate name: error: def "model" is defined multiple times

License

MIT OR Apache-2.0