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extern crate proc_macro;
use proc_macro::TokenStream;
use quote::{format_ident, quote};
use syn::{parse_macro_input, Data, DataStruct, DeriveInput, Fields, Visibility};
#[proc_macro_derive(Lenses)]
pub fn lenses_derive(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let data_struct: DataStruct;
if let Data::Struct(s) = input.data {
data_struct = s
} else {
panic!("`#[derive(Lenses)]` may only be applied to structs")
}
let fields: Fields;
if let Fields::Named(_) = data_struct.fields {
fields = data_struct.fields
} else {
panic!("`#[derive(Lenses)]` may only be applied to structs with named fields")
}
let struct_name = &input.ident;
let lens_visibility = match input.vis {
Visibility::Public(..) => quote!(pub),
Visibility::Crate(..) => quote!(),
Visibility::Restricted(..) => quote!(),
Visibility::Inherited => quote!(),
};
let lens_items = fields.iter().enumerate().map(|(index, field)| {
if let Some(field_name) = &field.ident {
let field_index = index as u64;
let field_type = &field.ty;
let lens_name = format_ident!(
"{}{}Lens",
struct_name.to_string(),
to_camel_case(&field_name.to_string())
);
let value_lens = if is_primitive(&field.ty) {
quote!(
#[allow(dead_code)]
impl pl_lens::ValueLens for #lens_name {
#[inline(always)]
fn get(&self, source: &#struct_name) -> #field_type {
(*source).#field_name.clone()
}
}
)
} else {
quote!()
};
quote!(
#[allow(dead_code)]
#[doc(hidden)]
#lens_visibility struct #lens_name;
#[allow(dead_code)]
impl pl_lens::Lens for #lens_name {
type Source = #struct_name;
type Target = #field_type;
#[inline(always)]
fn path(&self) -> pl_lens::LensPath {
pl_lens::LensPath::new(#field_index)
}
#[inline(always)]
fn mutate<'a>(&self, source: &'a mut #struct_name, target: #field_type) {
source.#field_name = target
}
}
#[allow(dead_code)]
impl pl_lens::RefLens for #lens_name {
#[inline(always)]
fn get_ref<'a>(&self, source: &'a #struct_name) -> &'a #field_type {
&(*source).#field_name
}
#[inline(always)]
fn get_mut_ref<'a>(&self, source: &'a mut #struct_name) -> &'a mut #field_type {
&mut (*source).#field_name
}
}
#value_lens
)
} else {
panic!("`#[derive(Lenses)]` may only be applied to structs with named fields")
}
});
let lenses_struct_name = format_ident!("{}Lenses", struct_name);
let lenses_struct_fields = fields.iter().map(|field| {
if let Some(field_name) = &field.ident {
let field_lens_name = format_ident!(
"{}{}Lens",
struct_name,
to_camel_case(&field_name.to_string())
);
if is_primitive(&field.ty) {
quote!(#field_name: #field_lens_name)
} else {
let field_parent_lenses_field_name = format_ident!("{}_lenses", field_name);
let field_parent_lenses_type_name =
format_ident!("{}Lenses", to_camel_case(&field_name.to_string()));
quote!(
#field_name: #field_lens_name,
#field_parent_lenses_field_name: #field_parent_lenses_type_name
)
}
} else {
panic!("`#[derive(Lenses)]` may only be applied to structs with named fields")
}
});
let lenses_struct = quote!(
#[allow(dead_code)]
#[doc(hidden)]
#lens_visibility struct #lenses_struct_name {
#(#lenses_struct_fields),*
}
);
let lenses_const_name = format_ident!("_{}Lenses", struct_name);
let lenses_const_fields = fields.iter().map(|field|
if let Some(field_name) = &field.ident {
let field_lens_name = format_ident!("{}{}Lens", struct_name, to_camel_case(&field_name.to_string()));
if is_primitive(&field.ty) {
quote!(#field_name: #field_lens_name)
} else {
let field_parent_lenses_field_name = format_ident!("{}_lenses", field_name);
let field_parent_lenses_type_name = format_ident!("_{}Lenses", to_camel_case(&field_name.to_string()));
quote!(
#field_name: #field_lens_name,
#field_parent_lenses_field_name: #field_parent_lenses_type_name
)
}
} else {
panic!("`#[derive(Lenses)]` may only be applied to structs with named fields")
}
);
let lenses_const = quote!(
#[allow(dead_code)]
#[allow(non_upper_case_globals)]
#[doc(hidden)]
#lens_visibility const #lenses_const_name: #lenses_struct_name = #lenses_struct_name {
#(#lenses_const_fields),*
};
);
let expanded = quote! {
#(#lens_items)*
#lenses_struct
#lenses_const
};
TokenStream::from(expanded)
}
fn is_primitive(ty: &syn::Type) -> bool {
let type_str = quote!(#ty).to_string();
match type_str.as_ref() {
"i8" | "i16" | "i32" | "i64" | "u8" | "u16" | "u32" | "u64" | "f32" | "f64" | "String" => {
true
}
_ => false,
}
}
fn to_camel_case(s: &str) -> String {
s.split('_')
.flat_map(|word| {
word.chars().enumerate().map(|(i, c)| {
if i == 0 {
c.to_uppercase().collect::<String>()
} else {
c.to_lowercase().collect()
}
})
})
.collect::<Vec<_>>()
.concat()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn to_camel_case_should_work() {
assert_eq!(to_camel_case("this_is_snake_case"), "ThisIsSnakeCase");
}
}