Partial Struct

Partial Struct is a procedural macro crate that generates “partial” versions of Rust structs. It creates new structs that contain a subset of the fields from your original struct—omitting those you specify via the attribute—and automatically provides bidirectional conversion functions.

Features

• Generate Partial Structs: Automatically create one or more partial structs for a given full struct. Each partial struct contains all fields from the full struct except those specified to omit.

• Custom Target Name: Optionally specify the name of the generated partial struct via a literal. If omitted, the generated struct is named "Partial".

• Custom Derives: Optionally add extra derives (e.g., Debug, Clone) to the generated partial struct using a derive(...) clause.

• Bidirectional Conversion: The macro implements two conversions: - A method on the generated partial struct (named to_<base_struct>() in snake case) that takes the omitted fields as parameters and reconstructs the full struct. - An implementation of From for the generated partial struct, so you can convert the full struct into its partial representation via .into().

Installation

Add the following to your Cargo.toml:

[dependencies] partial_struct = "0.1.0"

Usage

Annotate your struct with #[derive(Partial)] and attach one or more #[partial(...)] attributes to configure the output. The attribute supports three optional parts (order does not matter):

• An optional target name literal (e.g. "UserConstructor"). If omitted, the generated struct is named "Partial".
• An optional derive(...) clause listing trait identifiers to derive on the generated struct.
• An optional omit(...) clause listing the names of fields to omit from the generated struct.

Examples

Example 1: Explicit Target Name, Extra Derives, and Omitted Fields

#[derive(Partial)]
  #[partial("UserConstructor", derive(Debug, Clone), omit(id, secret))]
  pub struct User {
      id: uuid::Uuid,
      name: String,
      secret: String,
  }
  
This generates:

  #[derive(Debug, Clone)]
  pub struct UserConstructor {
      pub name: String,
  }
  
  impl UserConstructor {
      pub fn to_user(self, id: uuid::Uuid, secret: String) -> User {
          User { name: self.name, id, secret }
      }
  }
  
  impl From<User> for UserConstructor {
      fn from(full: User) -> Self {
          Self { name: full.name }
      }
  }

Example 2: Default Target Name

#[derive(Partial)]
  #[partial(derive(Debug), omit(x))]
  pub struct Car {
      x: u32,
      model: String,
  }

Since no target name is provided, the generated struct is named "PartialCar" and the conversion method is named "to_car()". Also, an implementation of From for PartialCar is provided.

Example 3: Multiple Partial Attributes

#[derive(Partial)]
  #[partial("UserInfo", derive(Debug, Serialize, Deserialize, Default, PartialEq, Eq), omit(password))]
  #[partial("UserCreation", derive(Debug, Serialize, Deserialize, Default, PartialEq, Eq), omit(id_user, password, registration_date, email_verified, user_rol))]
  pub struct User { ... }

This will generate two partial versions (UserInfo and UserCreation), each with its own conversion method.

How It Works

When you derive Partial on a struct, the macro:

1. Parses all #[partial(...)] attributes to determine the target names, extra derives, and which fields to omit.
2. For each attribute, generates a new partial struct containing all fields from the full struct except those omitted.
3. Implements a conversion method on the generated partial struct that takes the omitted fields as parameters and reconstructs the full struct.
4. Implements From for the generated partial struct, allowing conversion from the full struct via .into().

Minimizing Build Overhead

This crate minimizes compile time by enabling only the minimal syn features required for parsing. In the Cargo.toml for this crate, syn is included with:

syn = { version = "2.0.98", default-features = false, features = ["parsing"] }

License

This project is dual-licensed under the MIT or Apache-2.0 license, at your option.

Contributing

Contributions, issues, and feature requests are welcome. Please check the issue tracker on the project's repository for more information.

Author

Esteban estebanmff@outlook.com