Traits and functions to make writing proc macros more ergonomic.
proc_macro_roids = "0.8.0"Makes writing procedural macros much easier:
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::Span;
use proc_macro_roids::{DeriveInputStructExt, FieldExt, IdentExt};
use quote::quote;
use syn::{parse_macro_input, parse_quote, DeriveInput, Ident};
/// Derives a `Super` enum with a variant for each struct field:
///
/// ```rust,edition2021
/// use std::marker::PhantomData;
/// use super_derive::Super;
///
/// #[derive(Super)]
/// pub struct Man<T> {
/// #[super_derive(skip)]
/// name: String,
/// power_level: u64,
/// marker: PhantomData<T>,
/// }
/// ```
///
/// Generates:
///
/// ```rust,ignore
/// pub enum SuperMan {
/// U64(u64),
/// }
/// ```
#[proc_macro_derive(Super, attributes(super_derive))]
pub fn system_desc_derive(input: TokenStream) -> TokenStream {
let ast = parse_macro_input!(input as DeriveInput);
let enum_name = ast.ident.prepend("Super");
let fields = ast.fields();
let relevant_fields = fields
.iter()
.filter(|field| !field.is_phantom_data())
.filter(|field| !field.contains_tag(&parse_quote!(super_derive), &parse_quote!(skip)));
let variants = relevant_fields
.map(|field| {
let type_name = field.type_name();
let variant_name = type_name.to_string().to_uppercase();
let variant_name = Ident::new(&variant_name, Span::call_site());
quote! {
#variant_name(#type_name)
}
})
.collect::<Vec<_>>();
let token_stream2 = quote! {
pub enum #enum_name {
#(#variants,)*
}
};
token_stream2.into()
}1. Append additional `#[derive(..)]`s.
This works for function-like or attribute proc macros.
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro_roids::DeriveInputExt;
use quote::quote;
use syn::{parse_macro_input, parse_quote, DeriveInput};
#[proc_macro_attribute]
pub fn copy(_args: TokenStream, item: TokenStream) -> TokenStream {
// Example input:
//
// #[derive(Debug)]
// struct Struct;
let mut ast = parse_macro_input!(item as DeriveInput);
// Append the derives.
let derives = parse_quote!(Clone, Copy);
ast.append_derives(derives);
// Example output:
//
// #[derive(Debug, Clone, Copy)]
// struct Struct;
TokenStream::from(quote! { #ast })
}2. Append named fields.
This works for structs with named fields or unit structs.
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro_roids::FieldsNamedAppend;
use quote::quote;
use syn::{parse_macro_input, parse_quote, DeriveInput, FieldsNamed};
/// Example usage:
///
/// ```rust
/// use macro_crate::append_cd;
///
/// #[append_cd]
/// struct StructNamed { a: u32, b: i32 }
/// ```
#[proc_macro_attribute]
pub fn append_cd(_args: TokenStream, item: TokenStream) -> TokenStream {
// Example input:
//
// struct StructNamed { a: u32, b: i32 }
let mut ast = parse_macro_input!(item as DeriveInput);
// Append the fields.
let fields_additional: FieldsNamed = parse_quote!({ c: i64, d: usize });
ast.append_named(fields_additional);
// Example output:
//
// struct StructNamed { a: u32, b: i32, c: i64, d: usize }
TokenStream::from(quote! { #ast })
}3. Append unnamed fields (tuples).
This works for structs with unnamed fields or unit structs.
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro_roids::FieldsUnnamedAppend;
use quote::quote;
use syn::{parse_macro_input, parse_quote, DeriveInput, FieldsUnnamed};
/// Example usage:
///
/// ```rust
/// use macro_crate::append_i64_usize;
///
/// #[append_i64_usize]
/// struct StructUnit;
/// ```
#[proc_macro_attribute]
pub fn append_i64_usize(_args: TokenStream, item: TokenStream) -> TokenStream {
// Example input:
//
// struct StructUnit;
let mut ast = parse_macro_input!(item as DeriveInput);
// Append the fields.
let fields_additional: FieldsUnnamed = parse_quote!((i64, usize));
ast.append_unnamed(fields_additional);
// Example output:
//
// struct StructUnit(i64, usize);
TokenStream::from(quote! { #ast })
}4. Get newtype inner `Field`.
This works for structs with unnamed fields or unit structs.
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro_roids::DeriveInputNewtypeExt;
use quote::quote;
use syn::{parse_macro_input, parse_quote, DeriveInput, Type};
#[proc_macro_derive(Deref)]
pub fn derive_deref(item: TokenStream) -> TokenStream {
// Example input:
//
// #[derive(Deref)]
// struct Newtype(u32);
let mut ast = parse_macro_input!(item as DeriveInput);
// Get the inner field type.
let inner_type = ast.inner_type();
// Implement `Deref`
let type_name = &ast.ident;
let token_stream_2 = quote! {
#ast
impl std::ops::Deref for #type_name {
type Target = #inner_type;
fn deref(&self) -> &Self::Target {
&self.0
}
}
}
TokenStream::from(token_stream_2)
}5. `Ident` concatenation.
use proc_macro_roids::IdentExt;
use proc_macro2::Span;
use syn::Ident;
# fn main() {
let one = Ident::new("One", Span::call_site());
assert_eq!(Ident::new("OneSuffix", Span::call_site()), one.append("Suffix"));
assert_eq!(Ident::new("PrefixOne", Span::call_site()), one.prepend("Prefix"));
let two = Ident::new("Two", Span::call_site());
assert_eq!(Ident::new("OneTwo", Span::call_site()), one.append(&two));
assert_eq!(Ident::new("TwoOne", Span::call_site()), one.prepend(&two));
# }6. Accessing struct fields.
use proc_macro_roids::DeriveInputStructExt;
use syn::{parse_quote, DeriveInput, Fields};
# fn main() {
let ast: DeriveInput = parse_quote! {
struct Named {}
};
if let Fields::Named(..) = ast.fields() {
// do something
}
# }7. Inspecting `Field`s.
use proc_macro_roids::FieldExt;
use proc_macro2::Span;
use syn::{parse_quote, Fields, FieldsNamed, Lit, LitStr, Meta, MetaNameValue, NestedMeta};
let fields_named: FieldsNamed = parse_quote! {{
#[my::derive(tag::name(param = "value"))]
pub name: PhantomData<T>,
}};
let fields = Fields::from(fields_named);
let field = fields.iter().next().expect("Expected field to exist.");
assert_eq!(field.type_name(), "PhantomData");
assert!(field.is_phantom_data());
assert!(field.contains_tag(&parse_quote!(my::derive), &parse_quote!(tag::name)));
assert_eq!(
field.tag_parameter(
&parse_quote!(my::derive),
&parse_quote!(tag::name),
).expect("Expected parameter to exist."),
NestedMeta::Meta(Meta::NameValue(MetaNameValue {
path: parse_quote!(param),
eq_token: Default::default(),
lit: Lit::Str(LitStr::new("value", Span::call_site())),
})),
);8. (De)constructing `Fields`.
# use std::str::FromStr;
#
use proc_macro_roids::{DeriveInputStructExt, FieldsExt};
# use proc_macro2::{Span, TokenStream};
# use syn::{parse_quote, DeriveInput};
# use quote::quote;
#
// Need to generate code that instantiates `MyEnum::Struct`:
// enum MyEnum {
// Struct {
// field_0: u32,
// field_1: u32,
// }
// }
let ast: DeriveInput = parse_quote! {
struct Struct {
field_0: u32,
field_1: u32,
}
};
let fields = ast.fields();
let construction_form = fields.construction_form();
let tokens = quote! { MyEnum::Struct #construction_form };
let expected = TokenStream::from_str("MyEnum::Struct { field_0, field_1, }").unwrap();
assert_eq!(expected.to_string(), tokens.to_string());Note: The roids name is chosen because, although these functions make it easy to perform certain operations, they may not always be good ideas =D!
Licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)
at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.