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use quote::{quote, ToTokens};
use proc_macro2::{Span};
use syn::parse::{Result, Error};
use std::default::Default;
use std::ffi::CStr;
#[derive(Default)]
struct VariantMeta {
pub name: Option<syn::LitByteStr>,
}
impl VariantMeta {
pub fn from_attrs(attrs: &[syn::Attribute]) -> Result<Self> {
let mut opts = VariantMeta::default();
for attr in attrs {
if attr.path.is_ident("cstr") {
opts.parse_meta(attr.parse_meta()?)?
}
}
Ok(opts)
}
pub fn parse_meta(&mut self, meta: syn::Meta) -> Result<()> {
match meta {
syn::Meta::List(nvs) => {
for nv in nvs.nested {
match nv {
syn::NestedMeta::Meta(syn::Meta::NameValue(nv)) => self.parse_nv(nv)?,
_ => return Err(Error::new_spanned(nv, "expected named argument (KEY = VALUE)"))
}
}
}
_ => return Err(Error::new_spanned(meta, "missing arguments: expected `cstr(...)`"))
}
Ok(())
}
fn parse_nv(&mut self, nv: syn::MetaNameValue) -> Result<()> {
if let Some(ident) = nv.path.get_ident() {
if ident == "name" {
Self::check_not_set(&self.name, ident)?;
match nv.lit {
syn::Lit::Str(s) => {
let mut name = s.value();
name.push('\0');
if CStr::from_bytes_with_nul(name.as_bytes()).is_err() {
return Err(Error::new_spanned(s, "string cannot contain nul bytes"));
}
self.name = Some(syn::LitByteStr::new(name.as_bytes(), s.span()));
return Ok(());
}
lit => { return Err(Error::new_spanned(lit, "expected string literal")); }
}
}
}
Err(Error::new_spanned(nv.path, "invalid named argument"))
}
fn check_not_set<T>(field: &Option<T>, tokens: impl ToTokens) -> Result<()> {
if field.is_some() {
Err(Error::new_spanned(tokens, "duplicate named argument"))
} else {
Ok(())
}
}
}
fn ident_to_byte_str_lit(ident: &syn::Ident) -> syn::LitByteStr {
let cstring = {
let mut s = ident.to_string();
s.push('\0');
s
};
syn::LitByteStr::new(cstring.as_bytes(), Span::call_site())
}
fn check_enum_attrs(input: &syn::DeriveInput) -> Result<()> {
for attr in &input.attrs {
if attr.path.is_ident("cstr") {
return Err(Error::new_spanned(attr, "attribute must be placed on variants"));
}
}
Ok(())
}
fn get_name_mapping<'a>(input: &'a syn::DeriveInput, unit_variants_only: bool) -> Result<(Vec<&'a syn::Ident>, Vec<syn::LitByteStr>)> {
check_enum_attrs(input)?;
let variants = match &input.data {
syn::Data::Enum(enm) => &enm.variants,
_ => return Err(Error::new(Span::call_site(), "target must be an enum")),
};
let mut idents = Vec::with_capacity(variants.len());
let mut bytestrs = Vec::with_capacity(variants.len());
#[allow(unused_variables)]
for variant in variants {
if unit_variants_only && variant.fields != syn::Fields::Unit {
return Err(Error::new_spanned(variant, "variant cannot have fields"));
}
let ident = &variant.ident;
let opts = VariantMeta::from_attrs(&variant.attrs)?;
bytestrs.push(opts.name.unwrap_or_else(|| ident_to_byte_str_lit(&ident)));
idents.push(ident);
}
Ok((idents, bytestrs))
}
#[proc_macro_derive(AsCStr, attributes(cstr))]
pub fn derive_ascstr_enum(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = syn::parse_macro_input!(input as syn::DeriveInput);
let (var_idents, vals) = match get_name_mapping(&input, false) {
Ok(m) => m,
Err(e) => { return e.to_compile_error().into(); }
};
let ident = &input.ident;
let ts = quote! {
impl cstr_enum::AsCStr for #ident {
fn as_cstr(&self) -> &'static std::ffi::CStr {
match self {
#( Self::#var_idents{..} => unsafe {std::ffi::CStr::from_bytes_with_nul_unchecked(#vals) }, )*
}
}
}
};
ts.into()
}
#[proc_macro_derive(FromCStr, attributes(cstr))]
pub fn derive_fromcstr_enum(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = syn::parse_macro_input!(input as syn::DeriveInput);
let (var_idents, mut vals) = match get_name_mapping(&input, true) {
Ok(m) => m,
Err(e) => { return e.to_compile_error().into(); }
};
for v in vals.iter_mut() {
let bytes = v.value();
*v = syn::LitByteStr::new(&bytes[..bytes.len() - 1], v.span())
}
let ident = &input.ident;
let error_msg = syn::LitStr::new(&format!("unexpected string while parsing for {} variant", ident), Span::call_site());
let ts = quote! {
impl cstr_enum::FromCStr for #ident {
type Err = &'static str;
fn from_cstr(s: &std::ffi::CStr) -> Result<Self, Self::Err> {
match s.to_bytes() {
#( #vals => Ok(Self::#var_idents), )*
_ => Err(#error_msg)
}
}
}
};
ts.into()
}