cssparser-macros 0.1.0

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

extern crate phf_codegen;
extern crate proc_macro;
#[macro_use] extern crate quote;
extern crate syn;

use std::ascii::AsciiExt;

/// Find a `#[cssparser__assert_ascii_lowercase__data(string = "…", string = "…")]` attribute,
/// and panic if any string contains ASCII uppercase letters.
#[proc_macro_derive(cssparser__assert_ascii_lowercase,
                    attributes(cssparser__assert_ascii_lowercase__data))]
pub fn assert_ascii_lowercase(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = syn::parse_macro_input(&input.to_string()).unwrap();
    let data = list_attr(&input, "cssparser__assert_ascii_lowercase__data");

    for sub_attr in data {
        let string = sub_attr_value(sub_attr, "string");
        assert_eq!(*string, string.to_ascii_lowercase(),
                   "the expected strings must be given in ASCII lowercase");
    }

    "".parse().unwrap()
}

/// Find a `#[cssparser__max_len__data(string = "…", string = "…")]` attribute,
/// panic if any string contains ASCII uppercase letters,
/// emit a `MAX_LENGTH` constant with the length of the longest string.
#[proc_macro_derive(cssparser__max_len,
                    attributes(cssparser__max_len__data))]
pub fn max_len(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = syn::parse_macro_input(&input.to_string()).unwrap();
    let data = list_attr(&input, "cssparser__max_len__data");

    let lengths = data.iter().map(|sub_attr| sub_attr_value(sub_attr, "string").len());
    let max_length = lengths.max().expect("expected at least one string");

    let tokens = quote! {
        const MAX_LENGTH: usize = #max_length;
    };

    tokens.as_str().parse().unwrap()
}

/// On `struct $Name($ValueType)`, add a new static method
/// `fn map() -> &'static ::phf::Map<&'static str, $ValueType>`.
/// The map’s content is given as:
/// `#[cssparser__phf_map__kv_pairs(key = "…", value = "…", key = "…", value = "…")]`.
/// Keys are ASCII-lowercased.
#[proc_macro_derive(cssparser__phf_map,
                    attributes(cssparser__phf_map__kv_pairs))]
pub fn phf_map(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = syn::parse_macro_input(&input.to_string()).unwrap();
    let name = &input.ident;
    let value_type = match input.body {
        syn::Body::Struct(syn::VariantData::Tuple(ref fields)) if fields.len() == 1 => {
            &fields[0].ty
        }
        _ => panic!("expected tuple struct newtype, got {:?}", input.body)
    };

    let pairs: Vec<_> = list_attr(&input, "cssparser__phf_map__kv_pairs").chunks(2).map(|chunk| {
        let key = sub_attr_value(&chunk[0], "key");
        let value = sub_attr_value(&chunk[1], "value");
        (key.to_ascii_lowercase(), value)
    }).collect();

    let mut map = phf_codegen::Map::new();
    for &(ref key, value) in &pairs {
        map.entry(&**key, value);
    }

    let mut initializer_bytes = Vec::<u8>::new();
    let mut initializer_tokens = quote::Tokens::new();
    map.build(&mut initializer_bytes).unwrap();
    initializer_tokens.append(::std::str::from_utf8(&initializer_bytes).unwrap());

    let tokens = quote! {
        impl #name {
            #[inline]
            fn map() -> &'static ::phf::Map<&'static str, #value_type> {
                static MAP: ::phf::Map<&'static str, #value_type> = #initializer_tokens;
                &MAP
            }
        }
    };

    tokens.as_str().parse().unwrap()
}

/// Panic if the first attribute isn’t `#[foo(…)]` with the given name,
/// or return the parameters.
fn list_attr<'a>(input: &'a syn::DeriveInput, expected_name: &str) -> &'a [syn::NestedMetaItem] {
    for attr in &input.attrs {
        match attr.value {
            syn::MetaItem::List(ref name, ref nested) if name == expected_name => {
                return nested
            }
            _ => {}
        }
    }
    panic!("expected a {} attribute", expected_name)
}

/// Panic if `sub_attr` is not a name-value like `foo = "…"` with the given name,
/// or return the value.
fn sub_attr_value<'a>(sub_attr: &'a syn::NestedMetaItem, expected_name: &str) -> &'a str {
    match *sub_attr {
        syn::NestedMetaItem::MetaItem(
            syn::MetaItem::NameValue(ref name, syn::Lit::Str(ref value, _))
        )
        if name == expected_name => {
            value
        }
        _ => {
            panic!("expected a `{} = \"…\"` parameter to the attribute, got {:?}",
                   expected_name, sub_attr)
        }
    }
}