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|
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use quote::quote;
use syn::parse_quote;
use syn::spanned::Spanned;
use syn::{Error, Result};
/// Generate node properties.
#[proc_macro_attribute]
pub fn properties(_: TokenStream, item: TokenStream) -> TokenStream {
let impl_block = syn::parse_macro_input!(item as syn::ItemImpl);
expand(impl_block).unwrap_or_else(|err| err.to_compile_error()).into()
}
/// Expand a property impl block for a node.
fn expand(mut impl_block: syn::ItemImpl) -> Result<TokenStream2> {
// Split the node type into name and generic type arguments.
let (self_name, self_args) = parse_self(&*impl_block.self_ty)?;
// Rewrite the const items from values to keys.
let mut style_ids = vec![];
let mut modules = vec![];
for item in &mut impl_block.items {
if let syn::ImplItem::Const(item) = item {
let (style_id, module) = process_const(item, &self_name, &self_args)?;
style_ids.push(style_id);
modules.push(module);
}
}
// Here, we use the collected `style_ids` to provide a function that checks
// whether a property belongs to the node.
impl_block.items.insert(0, parse_quote! {
/// Check whether the property with the given type id belongs to `Self`.
pub fn has_property(id: StyleId) -> bool {
[#(#style_ids),*].contains(&id)
}
});
// Put everything into a module with a hopefully unique type to isolate
// it from the outside.
let module = quote::format_ident!("{}_types", self_name);
Ok(quote! {
#[allow(non_snake_case)]
mod #module {
use std::marker::PhantomData;
use once_cell::sync::Lazy;
use crate::eval::{Nonfolding, Property, StyleId};
use super::*;
#impl_block
#(#modules)*
}
})
}
/// Parse the name and generic type arguments of the node type.
fn parse_self(self_ty: &syn::Type) -> Result<(String, Vec<&syn::Type>)> {
// Extract the node type for which we want to generate properties.
let path = match self_ty {
syn::Type::Path(path) => path,
ty => return Err(Error::new(ty.span(), "must be a path type")),
};
// Split up the type into its name and its generic type arguments.
let last = path.path.segments.last().unwrap();
let self_name = last.ident.to_string();
let self_args = match &last.arguments {
syn::PathArguments::AngleBracketed(args) => args
.args
.iter()
.filter_map(|arg| match arg {
syn::GenericArgument::Type(ty) => Some(ty),
_ => None,
})
.collect(),
_ => vec![],
};
Ok((self_name, self_args))
}
/// Process a single const item.
fn process_const(
item: &mut syn::ImplItemConst,
self_name: &str,
self_args: &[&syn::Type],
) -> Result<(syn::Expr, syn::ItemMod)> {
// The type of the property's value is what the user of our macro wrote
// as type of the const ...
let value_ty = &item.ty;
// ... but the real type of the const becomes Key<#key_param>.
let key_param = if self_args.is_empty() {
quote! { #value_ty }
} else {
quote! { (#value_ty, #(#self_args),*) }
};
// The display name, e.g. `TextNode::STRONG`.
let name = format!("{}::{}", self_name, &item.ident);
// The default value of the property is what the user wrote as
// initialization value of the const.
let default = &item.expr;
let mut folder = None;
let mut nonfolding = Some(quote! {
impl<T: 'static> Nonfolding for Key<T> {}
});
// Look for a folding function like `#[fold(u64::add)]`.
for attr in &item.attrs {
if attr.path.is_ident("fold") {
let func: syn::Expr = attr.parse_args()?;
folder = Some(quote! {
const FOLDABLE: bool = true;
fn fold(inner: Self::Value, outer: Self::Value) -> Self::Value {
let f: fn(Self::Value, Self::Value) -> Self::Value = #func;
f(inner, outer)
}
});
nonfolding = None;
}
}
// The implementation of the `Property` trait.
let property_impl = quote! {
impl<T: 'static> Property for Key<T> {
type Value = #value_ty;
const NAME: &'static str = #name;
fn default() -> Self::Value {
#default
}
fn default_ref() -> &'static Self::Value {
static LAZY: Lazy<#value_ty> = Lazy::new(|| #default);
&*LAZY
}
#folder
}
#nonfolding
};
// The module that will contain the `Key` type.
let module_name = &item.ident;
// Generate the style id and module code.
let style_id = parse_quote! { StyleId::of::<#module_name::Key<#key_param>>() };
let module = parse_quote! {
#[allow(non_snake_case)]
mod #module_name {
use super::*;
pub struct Key<T>(pub PhantomData<T>);
impl<T> Copy for Key<T> {}
impl<T> Clone for Key<T> {
fn clone(&self) -> Self {
*self
}
}
#property_impl
}
};
// Replace type and initializer expression with the `Key`.
item.attrs.retain(|attr| !attr.path.is_ident("fold"));
item.ty = parse_quote! { #module_name::Key<#key_param> };
item.expr = parse_quote! { #module_name::Key(PhantomData) };
Ok((style_id, module))
}
|
