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#![deny(clippy::use_self)]
#[proc_macro_derive(Get, attributes(get))]
pub fn get(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let parsed_input = syn::parse_macro_input!(input as syn::DeriveInput);
get::expand(&parsed_input, false).unwrap().into()
}
#[proc_macro_derive(GetCopy, attributes(get))]
pub fn get_copy(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let parsed_input = syn::parse_macro_input!(input as syn::DeriveInput);
get::expand(&parsed_input, true).unwrap().into()
}
mod get {
use if_chain::if_chain;
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote, ToTokens};
use syn::{
parse::Parser, punctuated::Punctuated, Attribute, Data, DeriveInput, Expr, Field, Fields,
Index, Lit, Member, Meta, MetaNameValue, Token, Type,
};
#[derive(Default)]
struct GetAttribute {
method: Option<String>,
}
#[derive(Debug, Clone)]
enum GetNameValue {
Method(String),
}
pub fn expand(
input: &DeriveInput,
is_copy: bool,
) -> Result<TokenStream, Box<dyn std::error::Error>> {
let Data::Struct(target) = &input.data else {
return Err("expected struct as derive input".into())
};
let getters = match &target.fields {
Fields::Unnamed(fields) => expand_for_tuple_struct(fields.unnamed.iter(), is_copy)?,
Fields::Named(fields) => expand_for_struct(fields.named.iter(), is_copy)?,
_ => return Err("can not generate getters on a unit struct".into()),
};
let (impl_generics, ty_generics, where_clause) = &input.generics.split_for_impl();
let struct_name = &input.ident;
Ok(quote! {
#[automatically_derived]
impl #impl_generics #struct_name #ty_generics #where_clause {
#getters
}
})
}
fn expand_for_struct<'a>(
fields: impl Iterator<Item = &'a Field>,
is_copy: bool,
) -> Result<TokenStream, Box<dyn std::error::Error>> {
let mut tokens = TokenStream::new();
for field in fields {
let default_method_name = field.ident.as_ref().cloned().unwrap().to_string();
let method_name = field
.attrs
.iter()
.find(|attr| attr.path().is_ident("get"))
.cloned()
.map_or(Ok(default_method_name.clone()), |attr| {
GetAttribute::try_from(attr)
.map(|get_attr| get_attr.method.unwrap_or(default_method_name.clone()))
})?;
let getter = expand_getter(
field,
Member::Named(field.ident.as_ref().unwrap().clone()),
method_name.as_str(),
is_copy,
);
getter.to_tokens(&mut tokens);
}
Ok(tokens)
}
fn expand_for_tuple_struct<'a>(
fields: impl Iterator<Item = &'a Field>,
is_copy: bool,
) -> Result<TokenStream, Box<dyn std::error::Error>> {
let mut tokens = TokenStream::new();
for (i, field) in fields.enumerate() {
let attr: GetAttribute = field
.attrs
.iter()
.find(|a| a.path().is_ident("get"))
.cloned()
.ok_or("tuple fields are required to have an attribute")?
.try_into()?;
let method_name = attr
.method
.ok_or("tuple field attributes must specify the method name")?;
let getter = expand_getter(
field,
Member::Unnamed(Index {
index: i as u32,
span: Span::call_site(),
}),
method_name.as_str(),
is_copy,
);
getter.to_tokens(&mut tokens);
}
Ok(tokens)
}
fn expand_getter(
field: &Field,
field_name: Member,
method_name: &str,
is_copy: bool,
) -> TokenStream {
let method_name = format_ident!("{method_name}");
let field_type = &field.ty;
let field_lifetime = match &field.ty {
Type::Reference(type_ref) => Some(&type_ref.lifetime),
_ => None,
};
let method_args = if is_copy {
quote! { ( self ) }
} else {
quote! { ( & #field_lifetime self ) }
};
let method_type = if is_copy {
quote! { #field_type }
} else {
quote! { & #field_type }
};
let method_body = if is_copy {
quote! { { self . #field_name } }
} else {
quote! { { & self . #field_name } }
};
quote! {
pub fn
#method_name
#method_args
-> #method_type
#method_body
}
}
// This method might seem overly complicated but it will make it easy to add new fields to the
// GetAttribute struct in the future!
impl TryFrom<Attribute> for GetAttribute {
type Error = Box<dyn std::error::Error>;
fn try_from(attr: Attribute) -> Result<Self, Self::Error> {
if_chain! {
if attr.path().is_ident("get");
if let Meta::List(list) = &attr.meta;
then {
Ok(Punctuated::<MetaNameValue, Token![,]>::parse_terminated
.parse(list.tokens.clone().into())?
.into_iter()
.map(|n| n.try_into())
.collect::<Result<Vec<GetNameValue>, _>>()
.map(|v| match v.len() {
1..=3 => Ok(v),
_ => Err("expected at least 1 name value pair in attribute")
})??
.into_iter()
.fold(Self::default(), |_, n| match n {
GetNameValue::Method(s) => Self {
method: Some(s),
},
}))
} else {
Err("failed to parse attribute".into())
}
}
}
}
impl TryFrom<MetaNameValue> for GetNameValue {
type Error = Box<dyn std::error::Error>;
fn try_from(meta: MetaNameValue) -> Result<Self, Self::Error> {
if_chain! {
if let Some(name) = meta.path.get_ident().map(|ident| ident.to_string());
if let Expr::Lit(expr) = &meta.value;
if let Lit::Str(s) = &expr.lit;
if let "method" = name.as_str();
then {
Ok(Self::Method(s.value()))
} else {
Err("invalid name value pair in attribute".into())
}
}
}
}
}
|
