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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};
/// Turn a node into a class.
#[proc_macro_attribute]
pub fn class(_: 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 an 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 params = &impl_block.generics.params;
let self_ty = &*impl_block.self_ty;
let (self_name, self_args) = parse_self(self_ty)?;
let module = quote::format_ident!("{}_types", self_name);
let mut key_modules = vec![];
let mut construct = None;
let mut set = None;
for item in std::mem::take(&mut impl_block.items) {
match item {
syn::ImplItem::Const(mut item) => {
key_modules.push(process_const(
&mut item, params, self_ty, &self_name, &self_args,
)?);
impl_block.items.push(syn::ImplItem::Const(item));
}
syn::ImplItem::Method(method) => {
match method.sig.ident.to_string().as_str() {
"construct" => construct = Some(method),
"set" => set = Some(method),
_ => return Err(Error::new(method.span(), "unexpected method")),
}
}
_ => return Err(Error::new(item.span(), "unexpected item")),
}
}
let construct =
construct.ok_or_else(|| Error::new(impl_block.span(), "missing constructor"))?;
let set = if impl_block.items.is_empty() {
set.unwrap_or_else(|| {
parse_quote! {
fn set(_: &mut Args, _: &mut StyleMap) -> TypResult<()> {
Ok(())
}
}
})
} else {
set.ok_or_else(|| Error::new(impl_block.span(), "missing set method"))?
};
// Put everything into a module with a hopefully unique type to isolate
// it from the outside.
Ok(quote! {
#[allow(non_snake_case)]
mod #module {
use std::any::TypeId;
use std::marker::PhantomData;
use once_cell::sync::Lazy;
use crate::eval::{Construct, Nonfolding, Property, Set};
use super::*;
#impl_block
impl<#params> Construct for #self_ty {
#construct
}
impl<#params> Set for #self_ty {
#set
}
#(#key_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,
params: &syn::punctuated::Punctuated<syn::GenericParam, syn::Token![,]>,
self_ty: &syn::Type,
self_name: &str,
self_args: &[&syn::Type],
) -> Result<syn::ItemMod> {
// The module that will contain the `Key` type.
let module_name = &item.ident;
// 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_args>.
let key_args = 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<#params> Nonfolding for Key<#key_args> {}
});
// 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;
}
}
// Generate the module code.
let module = parse_quote! {
#[allow(non_snake_case)]
mod #module_name {
use super::*;
pub struct Key<VALUE, #params>(pub PhantomData<(VALUE, #key_args)>);
impl<#params> Copy for Key<#key_args> {}
impl<#params> Clone for Key<#key_args> {
fn clone(&self) -> Self {
*self
}
}
impl<#params> Property for Key<#key_args> {
type Value = #value_ty;
const NAME: &'static str = #name;
fn node_id() -> TypeId {
TypeId::of::<#self_ty>()
}
fn default() -> Self::Value {
#default
}
fn default_ref() -> &'static Self::Value {
static LAZY: Lazy<#value_ty> = Lazy::new(|| #default);
&*LAZY
}
#folder
}
#nonfolding
}
};
// 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_args> };
item.expr = parse_quote! { #module_name::Key(PhantomData) };
Ok(module)
}
|
