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extern crate proc_macro;
extern crate proc_macro2;
extern crate syn;
#[macro_use]
extern crate quote;
use proc_macro::TokenStream;
use syn::punctuated::Punctuated;
use syn::token::Comma;
use syn::{Attribute, DeriveInput, Field, Fields, Ident, Lit, Meta, NestedMeta};
#[proc_macro_derive(Yasec, attributes(yasec))]
pub fn derive(input: TokenStream) -> TokenStream {
let derive_input: DeriveInput = syn::parse(input).unwrap();
let gen = impl_yasec(&derive_input);
gen.into()
}
fn impl_yasec(input: &DeriveInput) -> proc_macro2::TokenStream {
use syn::Data::*;
let struct_name = &input.ident;
let inner_impl = match input.data {
Struct(ref ds) => match ds.fields {
Fields::Named(ref fields) => impl_yasec_for_struct(struct_name, &fields.named),
_ => panic!("yasec supports only named fields"),
},
_ => panic!("yasec only supports non-tuple structs"),
};
quote!(#inner_impl)
}
fn impl_yasec_for_struct(
struct_name: &Ident,
fields: &Punctuated<Field, Comma>,
) -> proc_macro2::TokenStream {
let field_assigns = fields.iter().map(gen_field_assign);
quote! {
impl Yasec for #struct_name {
fn with_context(context: ::yasec::Context<Self>) -> ::std::result::Result<Self, ::yasec::Error> {
let config = Self {
#(#field_assigns,)*
};
Ok(config)
}
}
}
}
fn gen_field_assign(field: &Field) -> proc_macro2::TokenStream {
match fetch_yasec_attr_from_field(field) {
Some(attr) => {
let list = fetch_list_from_attr(field, attr);
let from_value = find_item_in_list(field, &list, "from");
let opt_default = find_item_in_list(field, &list, "default");
gen_field_assign_for_struct_type(field, from_value, opt_default)
}
None => gen_field_assign_for_struct_type(field, None, None),
}
}
fn norm_path(path: &mut syn::TypePath) {
path.path.segments.iter_mut().for_each(|segment| {
let args = &mut segment.arguments;
if args.is_empty() {
return;
}
match args {
syn::PathArguments::AngleBracketed(ref mut x) if x.colon2_token.is_none() => {
x.colon2_token = Some(syn::Token!(::)([
proc_macro2::Span::call_site(),
proc_macro2::Span::call_site(),
]))
}
_ => (),
}
});
}
fn remove_quotes(val: &str) -> String {
val.chars().skip(1).take(val.len() - 2).collect()
}
fn gen_field_assign_for_struct_type(
field: &Field,
name: Option<&Lit>,
default: Option<&Lit>,
) -> proc_macro2::TokenStream {
let ident = &field.ident;
let var_name = name.map(|x| remove_quotes(&to_s(x))).unwrap_or_default();
let ident_str = to_s(ident).to_uppercase();
match &field.ty {
syn::Type::Path(path) => {
let mut path = path.clone();
norm_path(&mut path);
match default {
Some(_) => quote! {
#ident: #path :: with_context(
context
.with_var_name(#var_name)
.push_prefix(#ident_str.to_owned())
.with_default_var_value(Some(#default))
)?
},
None => quote! {
#ident: #path :: with_context(
context
.with_var_name(#var_name)
.push_prefix(#ident_str.to_owned())
.with_default_var_value(None)
)?
},
}
}
_ => panic!(format!("Expected field type to be a path: {:?}", ident)),
}
}
fn fetch_yasec_attr_from_field(field: &Field) -> Option<&Attribute> {
field.attrs.iter().find(|a| {
let path = &a.path;
let name = quote!(#path).to_string();
name == "yasec"
})
}
fn fetch_list_from_attr(field: &Field, attr: &Attribute) -> Punctuated<NestedMeta, Comma> {
let opt_meta = attr.interpret_meta().unwrap_or_else(|| {
panic!(
"Can not interpret meta of `yasec` attribute on field `{}`",
field_name(field)
)
});
match opt_meta {
Meta::List(l) => l.nested,
_ => panic!(
"`yasec` attribute on field `{}` must contain a list",
field_name(field)
),
}
}
fn find_item_in_list<'l, 'n>(
field: &Field,
list: &'l Punctuated<NestedMeta, Comma>,
item_name: &'n str,
) -> Option<&'l Lit> {
list.iter()
.map(|item| match item {
NestedMeta::Meta(meta) => match meta {
Meta::NameValue(name_value) => name_value,
_ => panic!(
"`yasec` attribute on field `{}` must contain name/value item",
field_name(field)
),
},
_ => panic!(
"Failed to process `yasec` attribute on field `{}`",
field_name(field)
),
})
.find(|name_value| {
let ident = &name_value.ident;
let name = quote!(#ident).to_string();
name == item_name
})
.map(|item| &item.lit)
}
fn field_name(field: &Field) -> String {
to_s(&field.ident)
}
fn to_s<T: quote::ToTokens>(node: &T) -> String {
quote!(#node).to_string()
}