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use super::attr::{FieldKind, Fields, LensAttrs};
use proc_macro2::{Ident, Span};
use quote::quote;
use std::collections::HashSet;
use syn::{spanned::Spanned, Data, GenericParam, TypeParam};
pub(crate) fn derive_lens_impl(
input: syn::DeriveInput,
) -> Result<proc_macro2::TokenStream, syn::Error> {
match &input.data {
Data::Struct(_) => derive_struct(&input),
Data::Enum(e) => Err(syn::Error::new(
e.enum_token.span(),
"Lens implementations cannot be derived from enums",
)),
Data::Union(u) => Err(syn::Error::new(
u.union_token.span(),
"Lens implementations cannot be derived from unions",
)),
}
}
fn derive_struct(input: &syn::DeriveInput) -> Result<proc_macro2::TokenStream, syn::Error> {
let ty = &input.ident;
let fields = if let syn::Data::Struct(syn::DataStruct { fields, .. }) = &input.data {
Fields::<LensAttrs>::parse_ast(fields)?
} else {
return Err(syn::Error::new(
input.span(),
"Lens implementations can only be derived from structs with named fields",
));
};
if fields.kind != FieldKind::Named {
return Err(syn::Error::new(
input.span(),
"Lens implementations can only be derived from structs with named fields",
));
}
let twizzled_name = if is_camel_case(&ty.to_string()) {
let temp_name = format!("{}_derived_lenses", to_snake_case(&ty.to_string()));
proc_macro2::Ident::new(&temp_name, proc_macro2::Span::call_site())
} else {
return Err(syn::Error::new(
ty.span(),
"Lens implementations can only be derived from CamelCase types",
));
};
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let mut lens_ty_idents = Vec::new();
let mut phantom_decls = Vec::new();
let mut phantom_inits = Vec::new();
for gp in input.generics.params.iter() {
if let GenericParam::Type(TypeParam { ident, .. }) = gp {
lens_ty_idents.push(quote! {#ident});
phantom_decls.push(quote! {std::marker::PhantomData<*const #ident>});
phantom_inits.push(quote! {std::marker::PhantomData});
}
}
let lens_ty_generics = quote! {
<#(#lens_ty_idents),*>
};
let defs = fields.iter().filter(|f| !f.attrs.ignore).map(|f| {
let field_name = &f.ident.unwrap_named();
let struct_docs = format!(
"Lens for the field `{field}` on [`{ty}`](super::{ty}).",
field = field_name,
ty = ty,
);
let fn_docs = format!(
"Creates a new lens for the field `{field}` on [`{ty}`](super::{ty}). \
Use [`{ty}::{field}`](super::{ty}::{field}) instead.",
field = field_name,
ty = ty,
);
quote! {
#[doc = #struct_docs]
#[allow(non_camel_case_types)]
#[derive(Debug, Copy, Clone)]
pub struct #field_name#lens_ty_generics(#(#phantom_decls),*);
impl #lens_ty_generics #field_name#lens_ty_generics{
#[doc = #fn_docs]
pub const fn new()->Self{
Self(#(#phantom_inits),*)
}
}
}
});
let used_params: HashSet<String> = input
.generics
.params
.iter()
.flat_map(|gp: &GenericParam| match gp {
GenericParam::Type(TypeParam { ident, .. }) => Some(ident.to_string()),
_ => None,
})
.collect();
let gen_new_param = |name: &str| {
let mut candidate: String = name.into();
let mut count = 1usize;
while used_params.contains(&candidate) {
candidate = format!("{}_{}", name, count);
count += 1;
}
Ident::new(&candidate, Span::call_site())
};
let func_ty_par = gen_new_param("F");
let val_ty_par = gen_new_param("V");
let impls = fields.iter().filter(|f| !f.attrs.ignore).map(|f| {
let field_name = &f.ident.unwrap_named();
let field_ty = &f.ty;
quote! {
impl #impl_generics druid::Lens<#ty#ty_generics, #field_ty> for #twizzled_name::#field_name#lens_ty_generics #where_clause {
fn with<#val_ty_par, #func_ty_par: FnOnce(&#field_ty) -> #val_ty_par>(&self, data: &#ty#ty_generics, f: #func_ty_par) -> #val_ty_par {
f(&data.#field_name)
}
fn with_mut<#val_ty_par, #func_ty_par: FnOnce(&mut #field_ty) -> #val_ty_par>(&self, data: &mut #ty#ty_generics, f: #func_ty_par) -> #val_ty_par {
f(&mut data.#field_name)
}
}
}
});
let associated_items = fields.iter().filter(|f| !f.attrs.ignore).map(|f| {
let field_name = &f.ident.unwrap_named();
let lens_field_name = f.attrs.lens_name_override.as_ref().unwrap_or(field_name);
quote! {
pub const #lens_field_name: #twizzled_name::#field_name#lens_ty_generics = #twizzled_name::#field_name::new();
}
});
let mod_docs = format!("Derived lenses for [`{}`].", ty);
let expanded = quote! {
#[doc = #mod_docs]
pub mod #twizzled_name {
#(#defs)*
}
#(#impls)*
#[allow(non_upper_case_globals)]
impl #impl_generics #ty #ty_generics #where_clause {
#(#associated_items)*
}
};
Ok(expanded)
}
fn char_has_case(c: char) -> bool {
c.is_lowercase() || c.is_uppercase()
}
fn is_camel_case(name: &str) -> bool {
let name = name.trim_matches('_');
if name.is_empty() {
return true;
}
!name.chars().next().unwrap().is_lowercase()
&& !name.contains("__")
&& !name.chars().collect::<Vec<_>>().windows(2).any(|pair| {
char_has_case(pair[0]) && pair[1] == '_' || char_has_case(pair[1]) && pair[0] == '_'
})
}
fn to_snake_case(mut str: &str) -> String {
let mut words = vec![];
str = str.trim_start_matches(|c: char| {
if c == '_' {
words.push(String::new());
true
} else {
false
}
});
for s in str.split('_') {
let mut last_upper = false;
let mut buf = String::new();
if s.is_empty() {
continue;
}
for ch in s.chars() {
if !buf.is_empty() && buf != "'" && ch.is_uppercase() && !last_upper {
words.push(buf);
buf = String::new();
}
last_upper = ch.is_uppercase();
buf.extend(ch.to_lowercase());
}
words.push(buf);
}
words.join("_")
}