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extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate synstructure;
#[macro_use]
extern crate quote;
decl_derive!([ErrorKind, attributes(msg)] => error_kind_derive);
fn error_kind_derive(s: synstructure::Structure) -> quote::Tokens {
let short_body = s.each_variant(|v| {
if let Some(msg) = find_msg(&v.ast().attrs) {
let metas = msg.nested;
if metas.is_empty() {
panic!("You have to implement `#[msg(short = \"your description\")]`");
}
let mut filterd = metas.iter().filter_map(process_short);
if let Some(tokens) = filterd.next() {
if filterd.next().is_some() {
panic!("Cannot implment short=.. multiple times");
}
tokens
} else {
panic!("You have to implement `short = ..` attribute")
}
} else {
let par_name = s.ast().ident.as_ref();
let variant_name = v.ast().ident.as_ref();
if par_name != variant_name {
quote!(concat!(#par_name, "::", #variant_name))
} else {
quote!(#par_name)
}
}
});
let mut has_detailed = false;
let detailed_body = s.each_variant(|v| {
if let Some(t) = process_detailed(v) {
has_detailed = true;
t
} else {
quote!(String::new())
}
});
let mut res = s.bound_impl(
quote!(::error_chain_mini::ErrorKind),
quote! {
fn short(&self) -> &str {
match *self { #short_body }
}
fn detailed(&self) -> String {
match *self { #detailed_body }
}
},
);
let display_body = if has_detailed {
quote!(write!(f, "{} {{ {} }}", self.short(), self.detailed()))
} else {
quote!(write!(f, "{}", self.short()))
};
let display = s.bound_impl(
quote!(::std::fmt::Display),
quote! {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
#display_body
}
},
);
res.append_all(display);
res
}
fn process_detailed(variant: &synstructure::VariantInfo) -> Option<quote::Tokens> {
let msg = find_msg(&variant.ast().attrs)?;
let nested = msg.nested;
let mut iter = nested.iter().skip_while(|nested| match nested {
syn::NestedMeta::Meta(syn::Meta::NameValue(nameval)) => nameval.ident != "detailed",
_ => panic!("Invlaid Value"),
});
let detailed = iter.next()?;
let s = if let syn::NestedMeta::Meta(syn::Meta::NameValue(nameval)) = detailed {
if let syn::Lit::Str(ref lit) = nameval.lit {
lit.value()
} else {
panic!("Only string is allowed after detailed=")
}
} else {
unreachable!();
};
macro_rules! get_nth {
($id: expr) => {{
let bi = variant.bindings().into_iter().nth($id);
if let Some(bi) = bi {
bi.binding
} else {
panic!("Invalid index {} for {:?}", $id, variant.prefix);
}
}};
}
let args = iter.take_while(|arg| {
if let syn::NestedMeta::Meta(syn::Meta::NameValue(_)) = arg {
false
} else {
true
}
}).map(|arg| match arg {
syn::NestedMeta::Literal(syn::Lit::Int(int)) => {
let idx = int.value() as usize;
let bi = get_nth!(idx);
quote!(#bi)
}
syn::NestedMeta::Meta(syn::Meta::Word(ident)) => {
if ident.as_ref().starts_with("_") {
if let Ok(idx) = ident.as_ref()[1..].parse::<usize>() {
let bi = get_nth!(idx);
return quote!(#bi);
}
}
if let Some(bi) = variant
.bindings()
.into_iter()
.find(|bi| bi.ast().ident.as_ref() == Some(ident))
{
let bi = bi.binding;
quote!(#bi)
} else {
panic!(
"Invalid argument {} for {:?}",
ident.as_ref(),
variant.prefix
);
}
}
_ => panic!("Invalid argument to detailed=.."),
});
Some(quote!(format!(#s #(, #args)*)))
}
fn process_short(nested: &syn::NestedMeta) -> Option<quote::Tokens> {
match nested {
syn::NestedMeta::Meta(syn::Meta::NameValue(nameval)) => {
if nameval.ident == "detailed" {
return None;
}
if nameval.ident != "short" {
panic!("only short=.. or detailed=.. is allowed");
}
if let syn::Lit::Str(ref lit_str) = nameval.lit {
let val = lit_str.value();
Some(quote!(#val))
} else {
panic!("Oly string literal is allowed after short")
}
}
_ => None,
}
}
fn find_msg(attrs: &[syn::Attribute]) -> Option<syn::MetaList> {
let mut res = None;
for attr in attrs {
let meta = attr.interpret_meta();
if let Some(syn::Meta::List(list)) = meta {
if list.ident == "msg" {
if res.is_some() {
panic!("Cannot have multiple `msg` attributes");
}
res = Some(list);
}
}
}
res
}