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#![doc = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/README.md"))]
use syn::{Error, Result, Variant};
use proc_macro::TokenStream;
use quote::quote;
const FUNC_ATTR: &'static str = "func";
const ASSOC_ATTR: &'static str = "assoc";
#[proc_macro_derive(Assoc, attributes(func, assoc))]
pub fn derive_assoc(input: TokenStream) -> TokenStream
{
impl_macro(&syn::parse(input).expect("Failed to parse macro input"))
.unwrap_or_else(syn::Error::into_compile_error)
.into()
}
fn impl_macro(ast: &syn::DeriveInput) -> Result<proc_macro2::TokenStream>
{
let name = &ast.ident;
let fn_attrs = ast.attrs
.iter()
.filter(|attr| attr.path.is_ident(FUNC_ATTR))
.map(|attr|
{
let s = attr.tokens.to_string();
match s[1..s.len()-1].parse::<proc_macro2::TokenStream>()
{
Ok(result) => Ok(result),
_ => Err(Error::new_spanned(attr, "Failed to parse attribute"))
}
})
.collect::<Result<Vec<proc_macro2::TokenStream>>>()?;
let fn_names = fn_attrs.iter()
.filter_map
(
|f| f.to_string()
.split("fn ")
.skip(1)
.next()
.map(|s| s.split("(").map(|s| s.trim()).next())
.map(|s| s.map(|s| s.to_string()))
)
.flatten()
.collect::<Vec<String>>();
let fn_options = fn_attrs.iter()
.filter_map
(
|f| f.to_string()
.split("->")
.last()
.map(|s|
{
let trimmed = s.trim();
trimmed.starts_with("Option") && trimmed[6..].trim().starts_with("<")
})
)
.collect::<Vec<bool>>();
let variants: Vec<&Variant> = if let syn::Data::Enum(data) = &ast.data
{
data.variants.iter().collect()
}
else
{
panic!("#[derive(Assoc)] only applicable to enums")
};
let functions: Vec<proc_macro2::TokenStream> = fn_attrs.iter()
.zip(fn_names.iter())
.zip(fn_options.into_iter())
.map(|((attr, fn_name), is_option)| build_variant_arms(&variants, attr, fn_name, is_option))
.collect::<Result<Vec<proc_macro2::TokenStream>>>()?;
Ok(quote!
{
impl #name
{
#(#functions)*
}
}.into())
}
fn build_variant_arms(variants: &Vec<&Variant>, attr: &proc_macro2::TokenStream, fn_name: &str, is_option: bool)
-> Result<proc_macro2::TokenStream>
{
let arms: Vec<proc_macro2::TokenStream> = variants.iter()
.map(|variant| build_variant_arm(variant, fn_name, is_option))
.collect::<Result<Vec<proc_macro2::TokenStream>>>()?;
Ok(quote!
{
#attr
{
match self
{
#(#arms),*
}
}
})
}
fn build_variant_arm(variant: &Variant, fn_name: &str, is_option: bool) -> Result<proc_macro2::TokenStream>
{
let var_ident = &variant.ident;
let fields = match &variant.fields
{
syn::Fields::Named(fields) =>
{
let named = fields.named.iter().map(|f|
{
let ident = &f.ident;
quote!(#ident: _)
}).collect::<Vec::<proc_macro2::TokenStream>>();
quote!({#(#named),*})
},
syn::Fields::Unnamed(fields) =>
{
let unnamed = fields.unnamed.iter().map(|_| quote!(_)).collect::<Vec::<proc_macro2::TokenStream>>();
quote!((#(#unnamed),*))
},
_ => quote!()
};
let assocs = variant
.attrs
.iter()
.filter(|assoc_attr| assoc_attr.path.is_ident(ASSOC_ATTR))
.map(|attr|
{
let s = attr.tokens.to_string();
let s = &s[1..s.len()-1];
let first_eq = match s.find("=")
{
Some(result) => result,
None => return Err(Error::new_spanned(attr, "Invalid `assoc` attribute, missing `=`"))
};
let r: (proc_macro2::TokenStream, proc_macro2::TokenStream) =
(
match s[..first_eq].trim().parse()
{
Ok(fn_name) => fn_name,
Err(_) => return Err(Error::new_spanned(attr, "Invalid `assoc` attribute, failed to parse left side"))
},
match s[first_eq+1..].trim().parse()
{
Ok(val) => val,
Err(_) => return Err(Error::new_spanned(attr, "Invalid `assoc` attribute, failed to parse right side"))
}
);
Ok(r)
})
.filter(|result|
{
match result
{
Ok((inner_name, _)) => inner_name.to_string() == fn_name,
Err(_) => true
}
})
.map(|result|
{
match result
{
Ok((_, val)) => Ok(val),
Err(e) => Err(e)
}
})
.collect::<Result<Vec<proc_macro2::TokenStream>>>()?;
match assocs.len()
{
0 if is_option => Ok(quote!{ Self::#var_ident #fields => None }),
0 => Err(Error::new_spanned(variant, format!("Missing `assoc` attribute for {}", fn_name))),
1 =>
{
let val = &assocs[0];
if is_option
{
if
{
let s = val.to_string();
let trimmed = s.trim();
trimmed.starts_with("Some") && trimmed[4..].trim().starts_with("(")
}
{
Ok(quote!{ Self::#var_ident #fields => #val })
}
else
{
Ok(quote!{ Self::#var_ident #fields => Some(#val) })
}
}
else
{
Ok(quote!{ Self::#var_ident #fields => #val })
}
}
_ => Err(Error::new_spanned(variant, format!("Too many `assoc` attributes for {}", fn_name)))
}
}
