nestify 0.3.3

Nestify offers a macro to simplify and beautify nested struct definitions in Rust, enabling cleaner, more readable code structures with less verbosity. It's especially valuable for handling API responses.
Documentation 
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use proc_macro2::{Span, TokenStream};
use quote::{ToTokens};
use syn::parse::{Parse, ParseStream};
use syn::{Token, AngleBracketedGenericArguments};
use syn::spanned::Spanned;

#[derive(Clone, Debug)]
pub struct FishHook {
    pub prefix: Token![||],
    pub generics: AngleBracketedGenericArguments,
}

impl FishHook {
    pub fn span(&self) -> Span {
        // will provide better span on a nightly compiler
        self.prefix.span().join(self.generics.span()).unwrap_or_else(|| self.prefix.span())
    }
}

impl Parse for FishHook {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let fish = Self {
            prefix: input.parse()?,
            generics: input.parse()?,
        };

        if let Some(tokens) = fish.generics.colon2_token {
            return Err(syn::Error::new(tokens.span(), ":: are not allowed in FishHook syntax"));
        }

        if fish.generics.args.iter().count() == 0 {
            return Err(syn::Error::new(fish.span(), "FishHook should not have empty or no generics"));
        }
        Ok(fish)
    }
}

impl ToTokens for FishHook {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        self.generics.to_tokens(tokens);
    }
}