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use proc_macro2::TokenStream;
use quote::ToTokens;
use syn::{parse::Error, MetaNameValue};
use crate::util::find_only;
#[derive(Debug, Clone, Copy)]
pub enum ConversionStrategy {
NoConversion,
Into,
}
pub struct DefaultAttr {
pub code: Option<TokenStream>,
conversion_strategy: Option<ConversionStrategy>,
}
impl DefaultAttr {
pub fn find_in_attributes(attrs: &[syn::Attribute]) -> Result<Option<Self>, Error> {
if let Some(default_attr) =
find_only(attrs.iter(), |attr| Ok(attr.path().is_ident("default")))?
{
match &default_attr.meta {
syn::Meta::Path(_) => Ok(Some(Self {
code: None,
conversion_strategy: None,
})),
syn::Meta::List(meta) => {
// If the meta contains exactly (_code = "...") take the string literal as the
// expression
if let Ok(ParseCodeHack(code_hack)) = syn::parse(meta.tokens.clone().into()) {
Ok(Some(Self {
code: Some(code_hack),
conversion_strategy: Some(ConversionStrategy::NoConversion),
}))
} else {
Ok(Some(Self {
code: Some(meta.tokens.clone()),
conversion_strategy: None,
}))
}
}
syn::Meta::NameValue(MetaNameValue { value, .. }) => Ok(Some(Self {
code: Some(value.into_token_stream()),
conversion_strategy: None,
})),
}
} else {
Ok(None)
}
}
pub fn conversion_strategy(&self) -> ConversionStrategy {
if let Some(conversion_strategy) = self.conversion_strategy {
// Conversion strategy already set
return conversion_strategy;
}
let code = if let Some(code) = &self.code {
code
} else {
// #[default] - so no conversion (`Default::default()` already has the correct type)
return ConversionStrategy::NoConversion;
};
match syn::parse::<syn::Lit>(code.clone().into()) {
Ok(syn::Lit::Str(_)) | Ok(syn::Lit::ByteStr(_)) => {
// A string literal - so we need a conversion in case we need to make it a `String`
return ConversionStrategy::Into;
}
_ => {}
}
// Not handled by one of the rules, so we don't convert it to avoid causing trouble
ConversionStrategy::NoConversion
}
}
struct ParseCodeHack(TokenStream);
impl syn::parse::Parse for ParseCodeHack {
fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
let ident: syn::Ident = input.parse()?;
if ident != "_code" {
return Err(Error::new(ident.span(), "Expected `_code`"));
}
input.parse::<syn::token::Eq>()?;
let code: syn::LitStr = input.parse()?;
let code: TokenStream = code.parse()?;
Ok(ParseCodeHack(code))
}
}