Merge pull request #373 from Areredify/visitor

add `Visitor` and friends

Author: nikomatsakis

chalk-derive/src/lib.rs

@@ -1,6 +1,7 @@
 extern crate proc_macro;
 
 use proc_macro::TokenStream;
+use proc_macro2::Span;
 use quote::{format_ident, quote};
 use syn::{parse_macro_input, Data, DeriveInput, GenericParam, Ident, TypeParamBound};
 
@@ -339,3 +340,219 @@ fn bounded_by_trait<'p>(param: &'p GenericParam, name: &str) -> Option<&'p Ident
         _ => None,
     }
 }
+
+/// Derives Visit for structs and enums for which one of the following is true:
+/// - It has a `#[has_interner(TheInterner)]` attribute
+/// - There is a single parameter `T: HasInterner` (does not have to be named `T`)
+/// - There is a single parameter `I: Interner` (does not have to be named `I`)
+#[proc_macro_derive(Visit, attributes(has_interner))]
+pub fn derive_visit(item: TokenStream) -> TokenStream {
+    let trait_name = Ident::new("Visit", Span::call_site());
+    let method_name = Ident::new("visit_with", Span::call_site());
+    derive_any_visit(item, trait_name, method_name)
+}
+
+/// Same as Visit, but derives SuperVisit instead
+#[proc_macro_derive(SuperVisit, attributes(has_interner))]
+pub fn derive_super_visit(item: TokenStream) -> TokenStream {
+    let trait_name = Ident::new("SuperVisit", Span::call_site());
+    let method_name = Ident::new("super_visit_with", Span::call_site());
+    derive_any_visit(item, trait_name, method_name)
+}
+
+fn derive_any_visit(item: TokenStream, trait_name: Ident, method_name: Ident) -> TokenStream {
+    let input = parse_macro_input!(item as DeriveInput);
+    let (impl_generics, ty_generics, where_clause_ref) = input.generics.split_for_impl();
+
+    let type_name = input.ident;
+    let body = derive_visit_body(&type_name, input.data);
+
+    if let Some(attr) = input.attrs.iter().find(|a| a.path.is_ident("has_interner")) {
+        // Hardcoded interner:
+        //
+        // impl Visit<ChalkIr> for Type {
+        //
+        // }
+        let arg = attr
+            .parse_args::<proc_macro2::TokenStream>()
+            .expect("Expected has_interner argument");
+
+        return TokenStream::from(quote! {
+            impl #impl_generics #trait_name < #arg > for #type_name #ty_generics #where_clause_ref {
+                fn #method_name <'i, R: VisitResult>(
+                    &self,
+                    visitor: &mut dyn Visitor < 'i, #arg, Result = R >,
+                    outer_binder: DebruijnIndex,
+                ) -> R
+                where
+                    I: 'i
+                {
+                    #body
+                }
+            }
+        });
+    }
+
+    match input.generics.params.len() {
+        1 => {}
+
+        0 => {
+            panic!("Visit derive requires a single type parameter or a `#[has_interner]` attr");
+        }
+
+        _ => {
+            panic!("Visit derive only works with a single type parameter");
+        }
+    };
+
+    let generic_param0 = &input.generics.params[0];
+
+    if let Some(param) = has_interner(&generic_param0) {
+        // HasInterner bound:
+        //
+        // Example:
+        //
+        // impl<T, _I> Visit<_I> for Binders<T>
+        // where
+        //     T: HasInterner<Interner = _I>,
+        // {
+        // }
+
+        let mut impl_generics = input.generics.clone();
+        impl_generics.params.extend(vec![GenericParam::Type(
+            syn::parse(quote! { _I: Interner }.into()).unwrap(),
+        )]);
+
+        let mut where_clause = where_clause_ref
+            .cloned()
+            .unwrap_or_else(|| syn::parse2(quote![where]).unwrap());
+        where_clause
+            .predicates
+            .push(syn::parse2(quote! { #param: HasInterner<Interner = _I> }).unwrap());
+        where_clause
+            .predicates
+            .push(syn::parse2(quote! { #param: Visit<_I> }).unwrap());
+
+        return TokenStream::from(quote! {
+            impl #impl_generics #trait_name < _I > for #type_name < #param >
+                #where_clause
+            {
+                fn #method_name <'i, R: VisitResult>(
+                    &self,
+                    visitor: &mut dyn Visitor < 'i, _I, Result = R >,
+                    outer_binder: DebruijnIndex,
+                ) -> R
+                where
+                    _I: 'i
+                {
+                    #body
+                }
+            }
+        });
+    }
+
+    // Interner bound:
+    //
+    // Example:
+    //
+    // impl<I> Visit<I> for Foo<I>
+    // where
+    //     I: Interner,
+    // {
+    // }
+
+    if let Some(i) = is_interner(&generic_param0) {
+        let impl_generics = &input.generics;
+
+        return TokenStream::from(quote! {
+            impl #impl_generics #trait_name < #i > for #type_name < #i >
+                #where_clause_ref
+            {
+                fn #method_name <'i, R: VisitResult>(
+                    &self,
+                    visitor: &mut dyn Visitor < 'i, #i, Result = R >,
+                    outer_binder: DebruijnIndex,
+                ) -> R
+                where
+                    I: 'i
+                {
+                    #body
+                }
+            }
+        });
+    }
+
+    panic!(
+        "derive({}) requires a parameter that implements HasInterner or Interner",
+        trait_name
+    );
+}
+
+/// Generates the body of the Visit impl
+fn derive_visit_body(type_name: &Ident, data: Data) -> proc_macro2::TokenStream {
+    match data {
+        Data::Struct(s) => {
+            let fields = s.fields.into_iter().map(|f| {
+                let name = f.ident.as_ref().expect("Unnamed field in a struct");
+                quote! {
+                   result = result.combine(self.#name.visit_with(visitor, outer_binder));
+                   if result.return_early() { return result; }
+                }
+            });
+            quote! {
+                let mut result = R::new();
+                #(#fields)*
+
+                result
+            }
+        }
+        Data::Enum(e) => {
+            let matches = e.variants.into_iter().map(|v| {
+                let variant = v.ident;
+                match &v.fields {
+                    syn::Fields::Named(fields) => {
+                        let fnames: &Vec<_> = &fields.named.iter().map(|f| &f.ident).collect();
+                        quote! {
+                            #type_name :: #variant { #(#fnames),* } => {
+                                let mut result = R::new();
+                                #(
+                                    result = result.combine(#fnames.visit_with(visitor, outer_binder));
+                                    if result.return_early() { return result; }
+                                )*
+                                result
+                            }
+                        }
+                    }
+
+                    syn::Fields::Unnamed(_fields) => {
+                        let names: Vec<_> = (0..v.fields.iter().count())
+                            .map(|index| format_ident!("a{}", index))
+                            .collect();
+                        quote! {
+                            #type_name::#variant( #(ref #names),* ) => {
+                                let mut result = R::new();
+                                #(
+                                    result = result.combine(#names.visit_with(visitor, outer_binder));
+                                    if result.return_early() { return result; }
+                                )*
+                                result
+                            }
+                        }
+                    }
+
+                    syn::Fields::Unit => {
+                        quote! {
+                            #type_name::#variant => R::new(),
+                        }
+                    }
+                }
+            });
+            quote! {
+                match *self {
+                    #(#matches)*
+                }
+            }
+        }
+        Data::Union(..) => panic!("Visit can not be derived for unions"),
+    }
+}