fn check_repr()

in gazebo_derive/src/coerce.rs [169:230]
58 lines of code
14 McCabe index (conditional complexity)

fn check_repr(input: &DeriveInput) -> syn::Result<()> {
    let mut has_repr = false;
    let mut errors = None;
    let mut push_error = |error| match &mut errors {
        Some(errors) => Error::combine(errors, error),
        None => errors = Some(error),
    };

    for attr in &input.attrs {
        if attr.path.is_ident("repr") {
            if let Err(error) = attr.parse_args_with(|input: ParseStream| {
                while !input.is_empty() {
                    let path = input.call(Path::parse_mod_style)?;
                    if path.is_ident("C") || path.is_ident("transparent") {
                        has_repr = true;
                    } else if path.is_ident("packed") {
                        // ignore
                    } else {
                        let meta_item_span = if input.peek(token::Paren) {
                            let group: TokenTree = input.parse()?;
                            quote!(#path #group)
                        } else if input.peek(Token![=]) {
                            let eq_token: Token![=] = input.parse()?;
                            let value: Expr = input.parse()?;
                            quote!(#path #eq_token #value)
                        } else {
                            quote!(#path)
                        };
                        let msg = if path.is_ident("align") {
                            "aligned repr on struct that implements Coerce is not supported"
                        } else {
                            "unrecognized repr on struct that implements Coerce"
                        };
                        push_error(Error::new_spanned(meta_item_span, msg));
                    }
                    if !input.is_empty() {
                        input.parse::<Token![,]>()?;
                    }
                }
                Ok(())
            }) {
                push_error(error);
            }
        }
    }

    if !has_repr {
        let mut requires_repr = Error::new(
            Span::call_site(),
            "Coerce trait requires #[repr(C)] or #[repr(transparent)]",
        );
        if let Some(errors) = errors {
            requires_repr.combine(errors);
        }
        errors = Some(requires_repr);
    }

    match errors {
        None => Ok(()),
        Some(errors) => Err(errors),
    }
}