annotation-rs

Compile-time annotation parser for rust

Features

Annotation

annotation-rs provides a derive macro Annotation to create annotation structure by struct, StructStruct, TupleStruct and NoFieldStruct are all supported.

use annotation_rs::Annotation;

#[derive(Annotation)]
struct NoField;

#[derive(Annotation)]
struct Tuple(i32, String);

#[derive(Annotation)]
struct Struct {
    int: i32,
    float: f64,
    bool: bool,
}

Types

• String: String in Rust.
• Bool: bool in Rust.
• Integer: any integer types in Rust.
• Float: any float types in Rust.
• Object: other annotation structure.
• Enum: defined enum, remember to use enum_value=trueoption.
• Vec: Vec of T(T can`t be Object, Vec or HashMap).
• HashMap<String, T>: HashMap of T mapping by String Skey. If you want to make a field optional, use Option<T> on the field type.

use annotation_rs::{AnnotationEnumValue, Annotation};

#[derive(Annotation)]
struct Bar;

#[derive(AnnotationEnumValue)]
enum SomeEnum {
    A,
    B
}

#[derive(Annotation)]
struct Foo {
    pub string: String,
    pub bool: bool,
    pub int: i32, // or other integer types like u32 ...
    pub float: f32, // or other float types like f64
    pub object: Bar, // any defined object
    #[field(enum_value=true)]
    pub enum_field: SomeEnum, // have to add enum_value option
    pub list: Vec<i32>, // nested type of vec can`t be Object, Vec or HashMap
    pub map: std::collections::HashMap<String, SomeEnum>,
    pub optional: Option<i32> // optional field
}

Options

• alias
  Generated reader will parse the field with the given name instead of its field name in Rust.

  #[derive(Annotation)]
  struct Foo {
      #[field(alias = "i32")]
      pub int32: i32,
  }

• default
  Set the default value for this field. If the value is not present when parsing, the default value will be set to the field, even the field is optional.Object, Vec or HashMap fields can`t have default value.

  #[derive(Annotation)]
  struct Foo {
      #[field(default = 1024)]
      pub int32: i32
  }

• enum_value
  use enum_value=true on Enum type field.

Enum

Use derive AnnotationEnumValue on Enum to create a Enum value type.

use annotation_rs::AnnotationEnumValue;

#[derive(AnnotationEnumValue)]
enum SomeEnum {
    A,
    B
}

And then, the enum can be used as a field type.

• variant_value attribute
  Customize a string corresponding value to variant(default is the snake case of variant name in Rust).

use annotation_rs::AnnotationEnumValue;

#[derive(AnnotationEnumValue)]
enum SomeEnum {
    #[variant_value("aaa")] // default is 'a'
    A,
    B
}

Parse annotations with synandquote

annotation_rs::AnnotationStructures<T> can be used in parse_macro_input!

let annotations = syn::parse_macro_inpit!(input as annotation_rs::AnnotationStructures<Foo>);

If you want to parse annotation from syn::Meta, use annotation_rs::AnnotationStructure::from_meta().
And annotation structure with value can be convert to token automatically. But the visibility of each field must be public.

use proc_macro::TokenStream;

#[derive(Annotation)]
struct Foo {
    #[field(default = 1024)]
    pub int32: i32
}

fn derive_fn(input: TokenStream) -> TokenStream {
    let annotations = syn::parse_macro_input!(input as annotation_rs::AnnotationStructures<Foo>);
    let attrs = annotations.attrs;

    TokenStream::from(quote::quote! {
        fn get_attrs() -> Vec<Foo> {
            vec![#(#attrs),*]
        }
    })
}

Generate derive macro

If you want to use builtin reader generator, enable annotation_reader feature. Macro generate_reader is used to generate a derive macro.

use annotation_rs::generate_reader;

generated_reader!(
    MyDerive,
    [StructAttribute1, StructAttribute2],
    [FieldAttribute1, FieldAttribute2]
);

The macro will generate a public derive, it can be use to read annotations of struct ,enum or union, and record the metadata by generate impl block.

Read annotations

Use the generated derive macro on a struct, and you can use the macro has_annotation and get_annotationto process annotations of the struct. The feature require nightly rustc because proc_macro_hygiene is required.

#![feature(proc_macro_hygiene)]
use annotation_rs::{get_annotation, has_annotation};

#[derive(MyDerive)]
#[StructAttribute1("some parameters")]
struct Foo {
    #[FieldAttribute1("some parameters")]
    field: i32
}

fn some_fn() {
    assert!(has_annotation!(Foo, StructAttribute1));
    assert!(has_annotation!(Foo::field, FieldAttribute1));
    let struct_attr1: Option<StructAttribute1> = get_annotation!(Foo, StructAttribute1);
    let field_attr1: Option<StructAttribute1> = get_annotation!(Foo::field, StructAttribute1);
}