style: Share more code between ToAnimatedValue and ToComputedValue derive.

I'm going to add a ToResolvedValue, and I don't want to add more copy-pasta.

This shouldn't change behavior.

Differential Revision: https://phabricator.services.mozilla.com/D26289

3 files changed, 122 insertions, 101 deletions

diff --git a/components/derive_common/cg.rs b/components/derive_common/cg.rs
index a5f15a0358e..7a8fbc24403 100644
--- a/components/derive_common/cg.rs
+++ b/components/derive_common/cg.rs
@@ -32,8 +32,8 @@ use synstructure::{self, BindStyle, BindingInfo, VariantAst, VariantInfo};
 pub fn propagate_clauses_to_output_type(
     where_clause: &mut Option<syn::WhereClause>,
     generics: &syn::Generics,
-    trait_path: Path,
-    trait_output: Ident,
+    trait_path: &Path,
+    trait_output: &Ident,
 ) {
     let where_clause = match *where_clause {
         Some(ref mut clause) => clause,
@@ -104,7 +104,7 @@ where
     })
 }
 
-pub fn fmap_trait_output(input: &DeriveInput, trait_path: &Path, trait_output: Ident) -> Path {
+pub fn fmap_trait_output(input: &DeriveInput, trait_path: &Path, trait_output: &Ident) -> Path {
     let segment = PathSegment {
         ident: input.ident.clone(),
         arguments: PathArguments::AngleBracketed(AngleBracketedGenericArguments {
diff --git a/components/style_derive/to_animated_value.rs b/components/style_derive/to_animated_value.rs
index 17c313e1ed0..ac231be3452 100644
--- a/components/style_derive/to_animated_value.rs
+++ b/components/style_derive/to_animated_value.rs
@@ -2,64 +2,42 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use derive_common::cg;
-use proc_macro2::{Span, TokenStream};
-use syn::{DeriveInput, Ident};
+use proc_macro2::TokenStream;
+use syn::DeriveInput;
 use synstructure::BindStyle;
+use to_computed_value;
 
-pub fn derive(mut input: DeriveInput) -> TokenStream {
-    let mut where_clause = input.generics.where_clause.take();
-    cg::propagate_clauses_to_output_type(
-        &mut where_clause,
-        &input.generics,
-        parse_quote!(crate::values::animated::ToAnimatedValue),
-        parse_quote!(AnimatedValue),
-    );
-    for param in input.generics.type_params() {
-        cg::add_predicate(
-            &mut where_clause,
-            parse_quote!(#param: crate::values::animated::ToAnimatedValue),
-        );
-    }
-
-    let to_body = cg::fmap_match(
-        &input,
-        BindStyle::Move,
-        |binding| quote!(crate::values::animated::ToAnimatedValue::to_animated_value(#binding)),
-    );
-    let from_body = cg::fmap_match(
-        &input,
-        BindStyle::Move,
-        |binding| quote!(crate::values::animated::ToAnimatedValue::from_animated_value(#binding)),
-    );
-
-    input.generics.where_clause = where_clause;
-    let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let animated_value_type = cg::fmap_trait_output(
-        &input,
-        &parse_quote!(crate::values::animated::ToAnimatedValue),
-        Ident::new("AnimatedValue", Span::call_site()),
-    );
-
-    quote! {
-        impl #impl_generics crate::values::animated::ToAnimatedValue for #name #ty_generics #where_clause {
-            type AnimatedValue = #animated_value_type;
+pub fn derive(input: DeriveInput) -> TokenStream {
+    let trait_impl = |from_body, to_body| {
+        quote! {
+            #[inline]
+            fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+                match animated {
+                    #from_body
+                }
+            }
 
-            #[allow(unused_variables)]
             #[inline]
             fn to_animated_value(self) -> Self::AnimatedValue {
                 match self {
                     #to_body
                 }
             }
+       }
+    };
 
-            #[inline]
-            fn from_animated_value(animated: Self::AnimatedValue) -> Self {
-                match animated {
-                    #from_body
-                }
-            }
-        }
-    }
+    // TODO(emilio): Consider optimizing away non-generic cases as well?
+    let non_generic_implementation = || None;
+
+    to_computed_value::derive_to_value(
+        input,
+        parse_quote!(crate::values::animated::ToAnimatedValue),
+        parse_quote!(AnimatedValue),
+        BindStyle::Move,
+        |_| false,
+        |binding| quote!(crate::values::animated::ToAnimatedValue::from_animated_value(#binding)),
+        |binding| quote!(crate::values::animated::ToAnimatedValue::to_animated_value(#binding)),
+        trait_impl,
+        non_generic_implementation,
+    )
 }
diff --git a/components/style_derive/to_computed_value.rs b/components/style_derive/to_computed_value.rs
index 21efae17c66..87d4f8ba014 100644
--- a/components/style_derive/to_computed_value.rs
+++ b/components/style_derive/to_computed_value.rs
@@ -3,53 +3,70 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use derive_common::cg;
-use proc_macro2::{Span, TokenStream};
-use syn::{DeriveInput, Ident};
-use synstructure::BindStyle;
+use proc_macro2::TokenStream;
+use syn::{DeriveInput, Ident, Path};
+use synstructure::{BindStyle, BindingInfo};
 
-pub fn derive(mut input: DeriveInput) -> TokenStream {
+pub fn derive_to_value(
+    mut input: DeriveInput,
+    trait_path: Path,
+    output_type_name: Ident,
+    bind_style: BindStyle,
+    // Returns whether to apply the field bound for a given item.
+    mut field_bound: impl FnMut(&BindingInfo) -> bool,
+    // Returns a token stream of the form: trait_path::from_foo(#binding)
+    mut call_from: impl FnMut(&BindingInfo) -> TokenStream,
+    mut call_to: impl FnMut(&BindingInfo) -> TokenStream,
+    // Returns a tokenstream of the form:
+    // fn from_function_syntax(foobar) -> Baz {
+    //     #first_arg
+    // }
+    //
+    // fn to_function_syntax(foobar) -> Baz {
+    //     #second_arg
+    // }
+    mut trait_impl: impl FnMut(TokenStream, TokenStream) -> TokenStream,
+    // if this is provided, the derive for non-generic types will be simplified
+    // to this token stream, which should be the body of the impl block.
+    non_generic_implementation: impl FnOnce() -> Option<TokenStream>,
+) -> TokenStream {
     let mut where_clause = input.generics.where_clause.take();
     cg::propagate_clauses_to_output_type(
         &mut where_clause,
         &input.generics,
-        parse_quote!(crate::values::computed::ToComputedValue),
-        parse_quote!(ComputedValue),
+        &trait_path,
+        &output_type_name,
     );
     let (to_body, from_body) = {
         let params = input.generics.type_params().collect::<Vec<_>>();
         for param in &params {
             cg::add_predicate(
                 &mut where_clause,
-                parse_quote!(#param: crate::values::computed::ToComputedValue),
+                parse_quote!(#param: #trait_path),
             );
         }
 
-        let to_body = cg::fmap_match(&input, BindStyle::Ref, |binding| {
-            let attrs = cg::parse_field_attrs::<ComputedValueAttrs>(&binding.ast());
-            if attrs.field_bound {
+        let to_body = cg::fmap_match(&input, bind_style, |binding| {
+            if field_bound(&binding) {
                 let ty = &binding.ast().ty;
 
                 let output_type = cg::map_type_params(
                     ty,
                     &params,
-                    &mut |ident| parse_quote!(<#ident as crate::values::computed::ToComputedValue>::ComputedValue),
+                    &mut |ident| parse_quote!(<#ident as #trait_path>::#output_type_name),
                 );
 
                 cg::add_predicate(
                     &mut where_clause,
                     parse_quote!(
-                        #ty: crate::values::computed::ToComputedValue<ComputedValue = #output_type>
+                        #ty: #trait_path<#output_type_name = #output_type>
                     ),
                 );
             }
-            quote! {
-                crate::values::computed::ToComputedValue::to_computed_value(#binding, context)
-            }
+            call_to(&binding)
         });
-        let from_body = cg::fmap_match(&input, BindStyle::Ref, |binding| {
-            quote! {
-                crate::values::computed::ToComputedValue::from_computed_value(#binding)
-            }
+        let from_body = cg::fmap_match(&input, bind_style, |binding| {
+            call_from(&binding)
         });
 
         (to_body, from_body)
@@ -58,39 +75,44 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
     input.generics.where_clause = where_clause;
     let name = &input.ident;
     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-
     if input.generics.type_params().next().is_none() {
-        return quote! {
-            impl #impl_generics crate::values::computed::ToComputedValue for #name #ty_generics
-            #where_clause
-            {
-                type ComputedValue = Self;
-
-                #[inline]
-                fn to_computed_value(
-                    &self,
-                    _context: &crate::values::computed::Context,
-                ) -> Self::ComputedValue {
-                    std::clone::Clone::clone(self)
+        if let Some(non_generic_implementation) = non_generic_implementation() {
+            return quote! {
+                impl #impl_generics #trait_path for #name #ty_generics
+                #where_clause
+                {
+                    #non_generic_implementation
                 }
-
-                #[inline]
-                fn from_computed_value(computed: &Self::ComputedValue) -> Self {
-                    std::clone::Clone::clone(computed)
-                }
-            }
-        };
+            };
+        }
     }
 
     let computed_value_type = cg::fmap_trait_output(
         &input,
-        &parse_quote!(crate::values::computed::ToComputedValue),
-        Ident::new("ComputedValue", Span::call_site()),
+        &trait_path,
+        &output_type_name,
     );
 
+    let impl_ = trait_impl(from_body, to_body);
+
     quote! {
-        impl #impl_generics crate::values::computed::ToComputedValue for #name #ty_generics #where_clause {
-            type ComputedValue = #computed_value_type;
+        impl #impl_generics #trait_path for #name #ty_generics #where_clause {
+            type #output_type_name = #computed_value_type;
+
+            #impl_
+        }
+    }
+}
+
+pub fn derive(input: DeriveInput) -> TokenStream {
+    let trait_impl = |from_body, to_body| {
+        quote! {
+            #[inline]
+            fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+                match *computed {
+                    #from_body
+                }
+            }
 
             #[allow(unused_variables)]
             #[inline]
@@ -99,15 +121,36 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
                     #to_body
                 }
             }
+       }
+    };
+
+    let non_generic_implementation = || {
+        Some(quote! {
+            type ComputedValue = Self;
+
+            #[inline]
+            fn to_computed_value(&self, _: &crate::values::computed::Context) -> Self::ComputedValue {
+                std::clone::Clone::clone(self)
+            }
 
             #[inline]
             fn from_computed_value(computed: &Self::ComputedValue) -> Self {
-                match *computed {
-                    #from_body
-                }
+                std::clone::Clone::clone(computed)
             }
-        }
-    }
+        })
+    };
+
+    derive_to_value(
+        input,
+        parse_quote!(crate::values::computed::ToComputedValue),
+        parse_quote!(ComputedValue),
+        BindStyle::Ref,
+        |binding| cg::parse_field_attrs::<ComputedValueAttrs>(&binding.ast()).field_bound,
+        |binding| quote!(crate::values::computed::ToComputedValue::from_computed_value(#binding)),
+        |binding| quote!(crate::values::computed::ToComputedValue::to_computed_value(#binding, context)),
+        trait_impl,
+        non_generic_implementation,
+    )
 }
 
 #[darling(attributes(compute), default)]