Initial support for generics

dylanmckay · dylanmckay · commit 14a1696b8b6d · 2021-05-24T23:06:51.000+12:00
Existing generic types and predicates are passed through unmodified.
diff --git a/diffus-derive-test/src/lib.rs b/diffus-derive-test/src/lib.rs
@@ -412,4 +412,61 @@ mod test {
             &vec![string::Edit::Copy('a'), string::Edit::Insert('\''),]
         );
     }
+
+    mod generics {
+        use diffus::Diffus;
+
+        pub trait Thing {
+            type Foo;
+            type Bar;
+        }
+
+        pub struct ConcreteThing;
+
+        impl Thing for ConcreteThing {
+            type Foo = String;
+            type Bar = i64;
+        }
+
+        #[derive(Diffus)]
+        pub struct TestNamedStruct<A> where A: Thing {
+            pub a: A::Foo,
+            pub inner: i32,
+        }
+
+        #[derive(Diffus)]
+        pub enum TestTuple<A> where A: Thing {
+            Hello {
+                bar: A::Bar,
+            },
+            UnitVariant,
+            TupleVariant(A::Bar, A::Bar),
+        }
+
+        #[derive(Diffus)]
+        pub struct TestUnnamedStruct<A>(pub A::Foo) where A: Thing;
+    }
+
+    #[test]
+    fn test() {
+        use self::generics::{ConcreteThing, TestNamedStruct};
+        use edit::string;
+
+        let a: TestNamedStruct<ConcreteThing> = TestNamedStruct { a: "a".to_string(), inner: 12 };
+        let ap = TestNamedStruct { a: "a'".to_string(), inner: 13 };
+
+        let diff = a.diff(&ap);
+        let actual_a = diff.change().unwrap().a.change().unwrap();
+        let actual_inner = diff.change().unwrap().inner.change().unwrap();
+
+        assert_eq!(
+            actual_a,
+            &vec![string::Edit::Copy('a'), string::Edit::Insert('\''),]
+        );
+
+        assert_eq!(
+            actual_inner,
+            &(&12, &13),
+        );
+    }
 }
diff --git a/diffus-derive/src/lib.rs b/diffus-derive/src/lib.rs
@@ -132,18 +132,33 @@ fn input_lifetime(generics: &syn::Generics) -> Option<&syn::Lifetime> {
     lifetime
 }
 
+struct Generics {
+    ty_generic_params: syn::punctuated::Punctuated<syn::GenericParam, syn::token::Comma>,
+
+    edited_ty_generic_params: syn::punctuated::Punctuated<syn::GenericParam, syn::token::Comma>,
+    edited_ty_where_clause: syn::WhereClause,
+
+    impl_diffable_generic_params: syn::punctuated::Punctuated<syn::GenericParam, syn::token::Comma>,
+    impl_diffable_where_clause: syn::WhereClause,
+
+    impl_lifetime: syn::Lifetime,
+}
+
 #[proc_macro_derive(Diffus)]
 pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input: syn::DeriveInput = syn::parse2(proc_macro2::TokenStream::from(input)).unwrap();
 
     let ident = &input.ident;
     let vis = &input.vis;
-    let where_clause = &input.generics.where_clause;
+
     let edited_ident = syn::parse_str::<syn::Path>(&format!("Edited{}", ident)).unwrap();
 
-    let data_lifetime = input_lifetime(&input.generics);
-    let default_lifetime = syn::parse_str::<syn::Lifetime>("'diffus_a").unwrap();
-    let impl_lifetime = data_lifetime.unwrap_or(&default_lifetime);
+    let Generics {
+        ty_generic_params,
+        edited_ty_generic_params, edited_ty_where_clause,
+        impl_diffable_generic_params, impl_diffable_where_clause,
+        impl_lifetime,
+    } = Generics::new(&input.generics, &input.data);
 
     #[cfg(feature = "serialize-impl")]
     let derive_serialize = Some(quote! { #[derive(serde::Serialize)] });
@@ -182,8 +197,8 @@ pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream
                 }
             });
 
-            let unit_enum_impl_lifetime = if has_non_unit_variant {
-                Some(impl_lifetime.clone())
+            let unit_enum_generic_params = if has_non_unit_variant {
+                Some(edited_ty_generic_params.clone())
             } else {
                 None
             };
@@ -262,12 +277,12 @@ pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream
 
             quote! {
                 #derive_serialize
-                #vis enum #edited_ident <#unit_enum_impl_lifetime> where #where_clause {
+                #vis enum #edited_ident <#unit_enum_generic_params> #edited_ty_where_clause {
                     #(#edit_variants),*
                 }
 
-                impl<#impl_lifetime> diffus::Diffable<#impl_lifetime> for #ident <#data_lifetime> where #where_clause {
-                    type Diff = diffus::edit::enm::Edit<#impl_lifetime, Self, #edited_ident <#unit_enum_impl_lifetime>>;
+                impl<#impl_diffable_generic_params> diffus::Diffable<#impl_lifetime> for #ident <#ty_generic_params> #impl_diffable_where_clause {
+                    type Diff = diffus::edit::enm::Edit<#impl_lifetime, Self, #edited_ident <#unit_enum_generic_params>>;
 
                     fn diff(&#impl_lifetime self, other: &#impl_lifetime Self) -> diffus::edit::Edit<#impl_lifetime, Self> {
                         match (self, other) {
@@ -290,12 +305,12 @@ pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream
                 syn::Fields::Named(_) => {
                     quote! {
                         #derive_serialize
-                        #vis struct #edited_ident<#impl_lifetime> where #where_clause {
+                        #vis struct #edited_ident<#edited_ty_generic_params> #edited_ty_where_clause {
                             #edit_fields
                         }
 
-                        impl<#impl_lifetime> diffus::Diffable<#impl_lifetime> for #ident <#data_lifetime> where #where_clause {
-                            type Diff = #edited_ident<#impl_lifetime>;
+                        impl<#impl_diffable_generic_params> diffus::Diffable<#impl_lifetime> for #ident <#ty_generic_params> #impl_diffable_where_clause {
+                            type Diff = #edited_ident<#edited_ty_generic_params>;
 
                             fn diff(&#impl_lifetime self, other: &#impl_lifetime Self) -> diffus::edit::Edit<#impl_lifetime, Self> {
                                 match ( #field_diffs ) {
@@ -311,10 +326,10 @@ pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream
                 syn::Fields::Unnamed(_) => {
                     quote! {
                         #derive_serialize
-                        #vis struct #edited_ident<#impl_lifetime> ( #edit_fields ) where #where_clause;
+                        #vis struct #edited_ident<#edited_ty_generic_params> ( #edit_fields ) #edited_ty_where_clause;
 
-                        impl<#impl_lifetime> diffus::Diffable<#impl_lifetime> for #ident <#data_lifetime> where #where_clause {
-                            type Diff = #edited_ident<#impl_lifetime>;
+                        impl<#impl_diffable_generic_params> diffus::Diffable<#impl_lifetime> for #ident <#ty_generic_params> #impl_diffable_where_clause {
+                            type Diff = #edited_ident<#edited_ty_generic_params>;
 
                             fn diff(&#impl_lifetime self, other: &#impl_lifetime Self) -> diffus::edit::Edit<#impl_lifetime, Self> {
                                 match ( #field_diffs ) {
@@ -330,9 +345,9 @@ pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream
                 syn::Fields::Unit => {
                     quote! {
                         #derive_serialize
-                        #vis struct #edited_ident< > where #where_clause;
+                        #vis struct #edited_ident< > #edited_ty_where_clause;
 
-                        impl<#impl_lifetime> diffus::Diffable<#impl_lifetime> for #ident< > where #where_clause {
+                        impl<#impl_lifetime> diffus::Diffable<#impl_lifetime> for #ident< > #impl_diffable_where_clause {
                             type Diff = #edited_ident;
 
                             fn diff(&#impl_lifetime self, other: &#impl_lifetime Self) -> diffus::edit::Edit<#impl_lifetime, Self> {
@@ -346,3 +361,115 @@ pub fn derive_diffus(input: proc_macro::TokenStream) -> proc_macro::TokenStream
         syn::Data::Union(_) => panic!("union type not supported yet"),
     })
 }
+
+impl Generics {
+    pub fn new(
+        input_generics: &syn::Generics,
+        data: &syn::Data,
+    ) -> Self {
+        let input_generic_params = &input_generics.params;
+        let input_where_clause = &input_generics.where_clause;
+        let empty_where_clause = input_generics.clone().make_where_clause().clone();
+
+        let generic_types_used = Self::collect_generic_types_used(input_generics, data);
+
+        let ty_generic_params = input_generic_params.clone();
+
+        let mut edited_ty_generic_params = ty_generic_params.clone();
+        let mut edited_ty_where_clause = input_where_clause.clone().unwrap_or(empty_where_clause.clone());
+
+        let mut impl_diffable_generic_params = input_generic_params.clone();
+        let mut impl_diffable_where_clause = input_where_clause.clone().unwrap_or(empty_where_clause);
+
+        let explicit_data_lifetime = input_lifetime(input_generics);
+        let impl_lifetime = explicit_data_lifetime.cloned().unwrap_or_else(|| {
+            let default_lifetime = syn::parse_str::<syn::Lifetime>("'diffus_a").unwrap();
+
+            // Add the lifetime into the generics lists.
+            impl_diffable_generic_params.insert(0, syn::GenericParam::Lifetime(syn::LifetimeDef::new(default_lifetime.clone())));
+            edited_ty_generic_params.insert(0, syn::GenericParam::Lifetime(syn::LifetimeDef::new(default_lifetime.clone())));
+
+            default_lifetime.clone()
+        });
+
+        // Ensure that all generic types that exist live for as long as the diffus lifetime.
+        impl_diffable_where_clause.predicates.extend(input_generics.type_params().map(|type_param| {
+            let where_predicate = quote!(#type_param : #impl_lifetime);
+            let where_predicate: syn::WherePredicate = syn::parse(where_predicate.into()).unwrap();
+            where_predicate
+        }));
+
+        // Ensure that all generic types actually used are diffable and live for as long as the
+        // diffus lifetime.
+        for generic_ty_path in generic_types_used {
+            let where_predicates = vec![
+                // quote!(<#generic_ty_path as diffus::Diffable<#impl_lifetime>>::Diff : diffus::Diffable<#impl_lifetime> + #impl_lifetime),
+                quote!(#generic_ty_path : diffus::Diffable<#impl_lifetime> + #impl_lifetime),
+            ];
+            let where_predicates: Vec<_> = where_predicates.into_iter().map(|wp| syn::parse::<syn::WherePredicate>(wp.into()).unwrap()).collect();
+
+            impl_diffable_where_clause.predicates.extend(where_predicates.clone());
+            edited_ty_where_clause.predicates.extend(where_predicates.clone());
+        }
+
+        Generics {
+            ty_generic_params,
+            edited_ty_generic_params, edited_ty_where_clause,
+            impl_diffable_generic_params, impl_diffable_where_clause,
+            impl_lifetime,
+        }
+    }
+
+    /// Collects all of the generic types used in a type including associated types.
+    fn collect_generic_types_used(
+        input_generics: &syn::Generics,
+        data: &syn::Data,
+    ) -> Vec<syn::Path> {
+        let all_possible_fields: Vec<&syn::Fields> = match *data {
+            syn::Data::Struct(ref s) => vec![&s.fields],
+            syn::Data::Enum(ref e) => e.variants.iter().map(|v| &v.fields).collect(),
+            syn::Data::Union(..) => Vec::new(), // unimplemented
+        };
+
+        let all_possible_types: Vec<&syn::Type> = all_possible_fields.into_iter().flat_map(|fields| match fields {
+            syn::Fields::Named(ref fields) => fields.named.iter().map(|f| &f.ty).collect(),
+            syn::Fields::Unnamed(ref fields) => fields.unnamed.iter().map(|f| &f.ty).collect(),
+            syn::Fields::Unit => Vec::new(),
+        }).collect();
+
+        let mut generic_types_used = Vec::new();
+        let mut remaining_types_to_check = all_possible_types.clone();
+
+        while let Some(type_to_check) = remaining_types_to_check.pop() {
+            match *type_to_check {
+                syn::Type::Path(ref path) => {
+                    if let Some(first_segment) = path.path.segments.first().map(|s| &s.ident) {
+                        let first_segment: syn::Ident = first_segment.clone().into();
+
+                        if input_generics.type_params().any(|type_param| type_param.ident == first_segment) {
+                            generic_types_used.push(path.path.clone());
+                        }
+                    }
+                },
+
+                syn::Type::Array(ref array) => remaining_types_to_check.push(&array.elem),
+                syn::Type::Group(ref group) => remaining_types_to_check.push(&group.elem),
+                syn::Type::Paren(ref paren) => remaining_types_to_check.push(&paren.elem),
+                syn::Type::Ptr(ref ptr) => remaining_types_to_check.push(&ptr.elem),
+                syn::Type::Reference(ref reference) => remaining_types_to_check.push(&reference.elem),
+                syn::Type::Slice(ref slice) => remaining_types_to_check.push(&slice.elem),
+                syn::Type::Tuple(ref tuple) => remaining_types_to_check.extend(tuple.elems.iter()),
+                syn::Type::Verbatim(..) |
+                    syn::Type::ImplTrait(..) |
+                    syn::Type::Infer(..) |
+                    syn::Type::Macro(..) |
+                    syn::Type::Never(..) |
+                    syn::Type::TraitObject(..) |
+                    syn::Type::BareFn(..) => (),
+                _ => (), // unknown/unsupported type
+            }
+        }
+
+        generic_types_used
+    }
+}
