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use proc_macro2::TokenStream;
use quote::quote;
use crate::info_structures::{Options, StructInfo};
/// Returns the Heads struct and a function to convert the original struct into a Heads instance.
pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, TokenStream) {
let visibility = if options.do_pub_extras {
info.vis.clone()
} else {
syn::parse_quote! { pub(super) }
};
let mut code = Vec::new();
let mut field_initializers = Vec::new();
let mut head_fields = Vec::new();
// Drop everything in the reverse order of what it was declared in. Fields that come later
// are only dependent on fields that came before them.
for field in info.fields.iter().rev() {
let field_name = &field.name;
if !field.self_referencing {
code.push(quote! { let #field_name = self.#field_name; });
if field.is_borrowed() {
field_initializers
.push(quote! { #field_name: ::ouroboros::macro_help::unbox(#field_name) });
} else {
field_initializers.push(quote! { #field_name });
}
let field_type = &field.typ;
head_fields.push(quote! { #visibility #field_name: #field_type });
} else {
// Heads are fields that do not borrow anything.
code.push(quote! { ::core::mem::drop(self.#field_name); });
}
}
for (ty, ident) in info.generic_consumers() {
head_fields.push(quote! { #ident: ::core::marker::PhantomData<#ty> });
field_initializers.push(quote! { #ident: ::core::marker::PhantomData });
}
let documentation = format!(
concat!(
"A struct which contains only the ",
"[head fields](https://docs.rs/ouroboros/latest/ouroboros/attr.self_referencing.html#definitions) of [`{0}`]({0})."
),
info.ident.to_string()
);
let generic_params = info.generic_params();
let generic_where = &info.generics.where_clause;
let heads_struct_def = quote! {
#[doc=#documentation]
#visibility struct Heads <#generic_params> #generic_where {
#(#head_fields),*
}
};
let documentation = concat!(
"This function drops all internally referencing fields and returns only the ",
"[head fields](https://docs.rs/ouroboros/latest/ouroboros/attr.self_referencing.html#definitions) of this struct."
).to_owned();
let documentation = if !options.do_no_doc {
quote! {
#[doc=#documentation]
}
} else {
quote! { #[doc(hidden)] }
};
let generic_args = info.generic_arguments();
let into_heads_fn = quote! {
#documentation
#[allow(clippy::drop_ref)]
#[allow(clippy::drop_copy)]
#[allow(clippy::drop_non_drop)]
#visibility fn into_heads(self) -> Heads<#(#generic_args),*> {
#(#code)*
Heads {
#(#field_initializers),*
}
}
};
(heads_struct_def, into_heads_fn)
}
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