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use proc_macro::{self, TokenStream};
use proc_macro2 as pm2;
use quote::ToTokens;
enum ConstraintItem {
Context(syn::Ident),
Access(Vec<syn::Type>),
}
impl syn::parse::Parse for ConstraintItem {
fn parse(input: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
let attr: syn::Ident = input.parse()?;
match attr.to_string().as_str() {
"context" => {
let _: syn::Token![=] = input.parse()?;
let value = input.parse()?;
Ok(ConstraintItem::Context(value))
}
"access" => {
let content;
let _: syn::token::Paren = syn::parenthesized!(content in input);
let punc =
syn::punctuated::Punctuated::<syn::Type, syn::Token![,]>::parse_terminated(
&content,
)?;
Ok(ConstraintItem::Access(punc.into_iter().collect()))
}
_ => Err(syn::Error::new_spanned(
attr,
"unsupported persian-rug constraint",
)),
}
}
}
struct ConstraintArgs {
pub context: syn::Ident,
pub used_types: Vec<syn::Type>,
}
impl syn::parse::Parse for ConstraintArgs {
fn parse(input: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
let punc =
syn::punctuated::Punctuated::<ConstraintItem, syn::Token![,]>::parse_terminated(input)?;
let mut context = None;
let mut used_types = Vec::new();
for item in punc.into_iter() {
match item {
ConstraintItem::Context(id) => {
context = Some(id);
}
ConstraintItem::Access(tys) => {
used_types.extend(tys);
}
}
}
context
.map(|context| Self {
context,
used_types,
})
.ok_or_else(|| {
syn::Error::new(
pm2::Span::call_site(),
"No context provided for constraints.",
)
})
}
}
/// Add the type constraints necessary for an impl using persian-rug.
///
/// Rust currently requires all relevant constraints to be written out
/// for every impl using a given type. For persian-rug in particular,
/// there are typically many constraints of a simple kind: for every
/// type owned by the given `Context`, there must be an `Owner`
/// implementation for the context and there must be a matching
/// `Contextual` implementation for the type. This macro simply
/// generates these constraints for you.
///
/// The attribute takes two types of argument:
/// - `context` specifies the name of the type of the context.
/// - `access(...)` specifies the types that this impl requires to
/// exist within that context. Typically each type requires some
/// other types to also exist in its context for it to be
/// well-formed. This argument needs to be given the transitive
/// closure of all such types, both direct and indirect dependencies
/// of the impl itself. It is unfortunately not possible at present
/// to find the indirect dependencies automatically.
///
/// Example:
/// ```rust
/// use persian_rug::{contextual, Context, Mutator, Proxy};
///
/// #[contextual(C)]
/// struct Foo<C: Context> {
/// _marker: core::marker::PhantomData<C>,
/// a: i32
/// }
///
/// struct Bar<C: Context> {
/// foo: Proxy<Foo<C>>
/// }
///
/// #[persian_rug::constraints(context = C, access(Foo<C>))]
/// impl<C> Bar<C> {
/// pub fn new<M: Mutator<Context=C>>(foo: Foo<C>, mut mutator: M) -> Self {
/// Self { foo: mutator.add(foo) }
/// }
/// }
/// ```
#[proc_macro_attribute]
pub fn constraints(args: TokenStream, input: TokenStream) -> TokenStream {
let mut target: syn::Item = syn::parse_macro_input!(input);
let generics = match &mut target {
syn::Item::Enum(e) => &mut e.generics,
syn::Item::Fn(f) => &mut f.sig.generics,
syn::Item::Impl(i) => &mut i.generics,
syn::Item::Struct(s) => &mut s.generics,
syn::Item::Trait(t) => &mut t.generics,
syn::Item::TraitAlias(t) => &mut t.generics,
syn::Item::Type(t) => &mut t.generics,
syn::Item::Union(u) => &mut u.generics,
_ => {
return syn::Error::new(
pm2::Span::call_site(),
"This attribute extends a where clause, or generic constraints. It cannot be used here."
)
.to_compile_error()
.into();
}
};
let ConstraintArgs {
context,
used_types,
} = syn::parse_macro_input!(args);
let wc = generics.make_where_clause();
let mut getters = syn::punctuated::Punctuated::<syn::TypeParamBound, syn::token::Add>::new();
getters.push(syn::parse_quote! { ::persian_rug::Context });
for ty in &used_types {
getters.push(syn::parse_quote! { ::persian_rug::Owner<#ty> });
}
wc.predicates.push(syn::parse_quote! {
#context: #getters
});
for ty in &used_types {
wc.predicates.push(syn::parse_quote! {
#ty: ::persian_rug::Contextual<Context = #context>
});
}
target.into_token_stream().into()
}
/// Convert an annotated struct into a `Context`
///
/// Each field marked with `#[table]` will be converted to be a
/// `Table` of values of the same type. An implementation of `Context`
/// will be provided. In addition, an implementation of `Owner` for
/// each field type will be derived for the overall struct.
///
/// Note that a `Context` can only contain one table of each type.
///
/// Example:
/// ```rust
/// use persian_rug::{contextual, persian_rug, Proxy};
///
/// #[contextual(MyRug)]
/// struct Foo {
/// a: i32
/// }
///
/// #[contextual(MyRug)]
/// struct Bar {
/// a: i32,
/// b: Proxy<Foo>
/// };
///
/// #[persian_rug]
/// struct MyRug(#[table] Foo, #[table] Bar);
/// ```
#[proc_macro_attribute]
pub fn persian_rug(_args: TokenStream, input: TokenStream) -> TokenStream {
let syn::DeriveInput {
attrs,
vis,
ident: ty_ident,
data,
generics,
} = syn::parse_macro_input!(input);
let (generics, ty_generics, wc) = generics.split_for_impl();
let mut impls = pm2::TokenStream::new();
let body = if let syn::Data::Struct(s) = data {
let mut fields = syn::punctuated::Punctuated::<syn::Field, syn::Token![,]>::new();
let mut process_field = |field: &syn::Field| {
let is_table = field.attrs.iter().any(|attr| attr.path.is_ident("table"));
let field_type = &field.ty;
let ident = field
.ident
.as_ref()
.map(|id| syn::Member::Named(id.clone()))
.unwrap_or_else(|| {
syn::Member::Unnamed(syn::Index {
index: fields.len() as u32,
span: pm2::Span::call_site(),
})
});
let vis = &field.vis;
let attrs = field
.attrs
.iter()
.filter(|a| !a.path.is_ident("table"))
.cloned()
.collect::<Vec<_>>();
if !is_table {
fields.push(field.clone());
} else {
fields.push(syn::Field {
attrs,
vis: vis.clone(),
ident: if let syn::Member::Named(id) = &ident {
Some(id.clone())
} else {
None
},
colon_token: field.colon_token,
ty: syn::parse_quote! {
::persian_rug::Table<#field_type>
},
});
impls.extend(quote::quote! {
impl #generics ::persian_rug::Owner<#field_type> for #ty_ident #ty_generics #wc {
fn add(&mut self, what: #field_type) -> ::persian_rug::Proxy<#field_type> {
self.#ident.push(what)
}
fn get(&self, what: &::persian_rug::Proxy<#field_type>) -> &#field_type {
self.#ident.get(what).unwrap()
}
fn get_mut(&mut self, what: &::persian_rug::Proxy<#field_type>) -> &mut #field_type {
self.#ident.get_mut(what).unwrap()
}
fn get_iter(&self) -> ::persian_rug::TableIterator<'_, #field_type> {
self.#ident.iter()
}
fn get_iter_mut(&mut self) -> ::persian_rug::TableMutIterator<'_, #field_type> {
self.#ident.iter_mut()
}
fn get_proxy_iter(&self) -> ::persian_rug::TableProxyIterator<'_, #field_type> {
self.#ident.iter_proxies()
}
}
});
}
};
match s.fields {
syn::Fields::Named(syn::FieldsNamed { named, .. }) => {
for field in named.iter() {
(process_field)(field);
}
quote::quote! {
#vis struct #ty_ident #generics #wc {
#fields
}
}
}
syn::Fields::Unnamed(syn::FieldsUnnamed { unnamed, .. }) => {
for field in unnamed.iter() {
(process_field)(field);
}
quote::quote! {
#vis struct #ty_ident #generics(
#fields
) #wc;
}
}
syn::Fields::Unit => {
quote::quote! {
#vis struct #ty_ident #generics #wc;
}
}
}
} else {
return syn::Error::new(
pm2::Span::call_site(),
"Only structs can be annotated as persian-rugs.",
)
.to_compile_error()
.into();
};
let attrs = {
let mut res = pm2::TokenStream::new();
for attr in attrs {
attr.to_tokens(&mut res);
}
res
};
let res = quote::quote! {
#attrs
#body
impl #generics ::persian_rug::Context for #ty_ident #ty_generics #wc {
fn add<T>(&mut self, what: T) -> ::persian_rug::Proxy<T>
where
#ty_ident #ty_generics: ::persian_rug::Owner<T>,
T: ::persian_rug::Contextual<Context=Self>
{
<Self as ::persian_rug::Owner<T>>::add(self, what)
}
fn get<T>(&self, what: &::persian_rug::Proxy<T>) -> &T
where
#ty_ident #ty_generics: ::persian_rug::Owner<T>,
T: ::persian_rug::Contextual<Context=Self>
{
<Self as ::persian_rug::Owner<T>>::get(self, what)
}
fn get_mut<T>(&mut self, what: &::persian_rug::Proxy<T>) -> &mut T
where
#ty_ident #ty_generics: ::persian_rug::Owner<T>,
T: ::persian_rug::Contextual<Context=Self>
{
<Self as ::persian_rug::Owner<T>>::get_mut(self, what)
}
fn get_iter<T>(&self) -> ::persian_rug::TableIterator<'_, T>
where
#ty_ident #ty_generics: ::persian_rug::Owner<T>,
T: ::persian_rug::Contextual<Context=Self>
{
<Self as ::persian_rug::Owner<T>>::get_iter(self)
}
fn get_iter_mut<T>(&mut self) -> ::persian_rug::TableMutIterator<'_, T>
where
#ty_ident #ty_generics: ::persian_rug::Owner<T>,
T: ::persian_rug::Contextual<Context=Self>
{
<Self as ::persian_rug::Owner<T>>::get_iter_mut(self)
}
fn get_proxy_iter<T>(&self) -> ::persian_rug::TableProxyIterator<'_, T>
where
#ty_ident #ty_generics: ::persian_rug::Owner<T>,
T: ::persian_rug::Contextual<Context=Self>
{
<Self as ::persian_rug::Owner<T>>::get_proxy_iter(self)
}
}
#impls
};
res.into()
}
/// Provide a implementation of `Contextual` for a type.
///
/// This is a very simple derive-style macro, that creates an
/// impl for `Contextual` for the type it annotates. It takes
/// one argument, which is the `Context` type that this
/// type belongs to.
///
/// Example:
/// ```rust
/// use persian_rug::{contextual, Context};
///
/// #[contextual(C)]
/// struct Foo<C: Context> {
/// _marker: core::marker::PhantomData<C>
/// }
/// ```
/// which is equivalent to the following:
/// ```rust
/// use persian_rug::{Context, Contextual};
///
/// struct Foo<C: Context> {
/// _marker: core::marker::PhantomData<C>
/// }
///
/// impl<C: Context> Contextual for Foo<C> {
/// type Context = C;
/// }
/// ```
#[proc_macro_attribute]
pub fn contextual(args: TokenStream, input: TokenStream) -> TokenStream {
let body = pm2::TokenStream::from(input.clone());
let syn::DeriveInput {
ident, generics, ..
} = syn::parse_macro_input!(input);
if args.is_empty() {
return syn::Error::new(
pm2::Span::call_site(),
"You must specify the associated context when using contextual.",
)
.to_compile_error()
.into();
}
let context: syn::Type = syn::parse_macro_input!(args);
let (generics, ty_generics, wc) = generics.split_for_impl();
let res = quote::quote! {
#body
impl #generics ::persian_rug::Contextual for #ident #ty_generics #wc {
type Context = #context;
}
};
res.into()
}