Auto merge of #18200 - servo:derive-all-the-things, r=emilio

Introduce style_derive::cg

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9 files changed, 291 insertions, 485 deletions

diff --git a/components/style_derive/animate.rs b/components/style_derive/animate.rs
index 5ce1040e94c..888a5e61c8e 100644
--- a/components/style_derive/animate.rs
+++ b/components/style_derive/animate.rs
@@ -2,56 +2,29 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
-use std::borrow::Cow;
 use syn;
-use synstructure;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(where_predicate(syn::Ty::Path(None, param.ident.clone().into())))
-    }
+    let trait_path = &["values", "animated", "Animate"];
+    let (impl_generics, ty_generics, mut where_clause) =
+        cg::trait_parts(&input, trait_path);
 
-    let variants = variants(&input);
+    let variants = cg::variants(&input);
     let mut match_body = quote!();
     match_body.append_all(variants.iter().map(|variant| {
-        let name = match input.body {
-            syn::Body::Struct(_) => Cow::Borrowed(&input.ident),
-            syn::Body::Enum(_) => {
-                Cow::Owned(syn::Ident::from(format!("{}::{}", input.ident, variant.ident)))
-            },
-        };
-        let (this_pattern, this_info) = synstructure::match_pattern(
-            &name,
-            &variant.data,
-            &synstructure::BindOpts::with_prefix(
-                synstructure::BindStyle::Ref,
-                "this".to_owned(),
-            ),
-        );
-        let (other_pattern, other_info) = synstructure::match_pattern(
-            &name,
-            &variant.data,
-            &synstructure::BindOpts::with_prefix(
-                synstructure::BindStyle::Ref,
-                "other".to_owned(),
-            ),
-        );
-        let (result_value, result_info) = synstructure::match_pattern(
-            &name,
-            &variant.data,
-            &synstructure::BindOpts::with_prefix(
-                synstructure::BindStyle::Move,
-                "result".to_owned(),
-            ),
-        );
+        let name = cg::variant_ctor(&input, variant);
+        let (this_pattern, this_info) = cg::ref_pattern(&name, variant, "this");
+        let (other_pattern, other_info) = cg::ref_pattern(&name, variant, "other");
+        let (result_value, result_info) = cg::value(&name, variant, "result");
         let mut computations = quote!();
         let iter = result_info.iter().zip(this_info.iter().zip(&other_info));
         computations.append_all(iter.map(|(result, (this, other))| {
-            where_clause.predicates.push(where_predicate(this.field.ty.clone()));
+            where_clause.predicates.push(
+                cg::where_predicate(this.field.ty.clone(), trait_path),
+            );
             quote! {
                 let #result = ::values::animated::Animate::animate(#this, #other, procedure)?;
             }
@@ -84,40 +57,3 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         }
     }
 }
-
-fn variants(input: &syn::DeriveInput) -> Cow<[syn::Variant]> {
-    match input.body {
-        syn::Body::Enum(ref variants) => (&**variants).into(),
-        syn::Body::Struct(ref data) => {
-            vec![syn::Variant {
-                ident: input.ident.clone(),
-                attrs: input.attrs.clone(),
-                data: data.clone(),
-                discriminant: None,
-            }].into()
-        },
-    }
-}
-
-fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(
-        syn::WhereBoundPredicate {
-            bound_lifetimes: vec![],
-            bounded_ty: ty,
-            bounds: vec![syn::TyParamBound::Trait(
-                syn::PolyTraitRef {
-                    bound_lifetimes: vec![],
-                    trait_ref: syn::Path {
-                        global: true,
-                        segments: vec![
-                            "values".into(),
-                            "animated".into(),
-                            "Animate".into(),
-                        ],
-                    },
-                },
-                syn::TraitBoundModifier::None,
-            )],
-        },
-    )
-}
diff --git a/components/style_derive/cg.rs b/components/style_derive/cg.rs
new file mode 100644
index 00000000000..af60591d7c6
--- /dev/null
+++ b/components/style_derive/cg.rs
@@ -0,0 +1,219 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use quote::Tokens;
+use std::borrow::Cow;
+use std::iter;
+use syn::{AngleBracketedParameterData, Body, DeriveInput, Ident, ImplGenerics};
+use syn::{Path, PathParameters, PathSegment, PolyTraitRef, QSelf};
+use syn::{TraitBoundModifier, Ty, TyGenerics, TyParam, TyParamBound, TypeBinding};
+use syn::{Variant, WhereBoundPredicate, WhereClause, WherePredicate};
+use syn::visit::{self, Visitor};
+use synstructure::{self, BindOpts, BindStyle, BindingInfo};
+
+pub fn fmap_match<F>(
+    input: &DeriveInput,
+    bind_style: BindStyle,
+    mut f: F,
+) -> Tokens
+where
+    F: FnMut(BindingInfo) -> Tokens,
+{
+    synstructure::each_variant(input, &bind_style.into(), |fields, variant| {
+        let name = variant_ctor(input, variant);
+        let (mapped, mapped_fields) = value(&name, variant, "mapped");
+        let fields_pairs = fields.into_iter().zip(mapped_fields);
+        let mut computations = quote!();
+        computations.append_all(fields_pairs.map(|(field, mapped_field)| {
+            let expr = f(field);
+            quote! { let #mapped_field = #expr; }
+        }));
+        computations.append(mapped);
+        Some(computations)
+    })
+}
+
+pub fn fmap_trait_parts<'a>(
+    input: &'a DeriveInput,
+    trait_path: &[&str],
+    trait_output: &str,
+) -> (ImplGenerics<'a>, TyGenerics<'a>, WhereClause, Path) {
+    let (impl_generics, ty_generics, where_clause) = trait_parts(input, trait_path);
+    let output_ty = PathSegment {
+        ident: input.ident.clone(),
+        parameters: PathParameters::AngleBracketed(AngleBracketedParameterData {
+            lifetimes: input.generics.lifetimes.iter().map(|l| l.lifetime.clone()).collect(),
+            types: input.generics.ty_params.iter().map(|ty| {
+                Ty::Path(
+                    Some(QSelf {
+                        ty: Box::new(Ty::Path(None, ty.ident.clone().into())),
+                        position: trait_path.len(),
+                    }),
+                    path(trait_path.iter().chain(iter::once(&trait_output))),
+                )
+            }).collect(),
+            .. Default::default()
+        }),
+    }.into();
+    (impl_generics, ty_generics, where_clause, output_ty)
+}
+
+fn fmap_trait_where_predicate(
+    bounded_ty: Ty,
+    trait_path: &[&str],
+    trait_output: Option<(&str, Ty)>,
+) -> WherePredicate {
+    WherePredicate::BoundPredicate(WhereBoundPredicate {
+        bound_lifetimes: vec![],
+        bounded_ty,
+        bounds: vec![TyParamBound::Trait(
+            PolyTraitRef {
+                bound_lifetimes: vec![],
+                trait_ref: fmap_trait_ref(trait_path, trait_output),
+            },
+            TraitBoundModifier::None
+        )],
+    })
+}
+
+fn fmap_trait_ref(path: &[&str], output: Option<(&str, Ty)>) -> Path {
+    let (name, parent) = path.split_last().unwrap();
+    let last_segment = PathSegment {
+        ident: (*name).into(),
+        parameters: PathParameters::AngleBracketed(
+            AngleBracketedParameterData {
+                bindings: output.into_iter().map(|(param, ty)| {
+                    TypeBinding { ident: param.into(), ty }
+                }).collect(),
+                .. Default::default()
+            }
+        )
+    };
+    Path {
+        global: true,
+        segments: {
+            parent
+                .iter()
+                .cloned()
+                .map(Into::into)
+                .chain(iter::once(last_segment))
+                .collect()
+        },
+    }
+}
+
+pub fn is_parameterized(ty: &Ty, params: &[TyParam]) -> bool {
+    struct IsParameterized<'a> {
+        params: &'a [TyParam],
+        has_free: bool,
+    }
+
+    impl<'a> Visitor for IsParameterized<'a> {
+        fn visit_path(&mut self, path: &Path) {
+            if !path.global && path.segments.len() == 1 {
+                if self.params.iter().any(|param| param.ident == path.segments[0].ident) {
+                    self.has_free = true;
+                }
+            }
+            visit::walk_path(self, path);
+        }
+    }
+
+    let mut visitor = IsParameterized { params: params, has_free: false };
+    visitor.visit_ty(ty);
+    visitor.has_free
+}
+
+pub fn path<S>(segments: S) -> Path
+where
+    S: IntoIterator,
+    <S as IntoIterator>::Item: AsRef<str>,
+{
+    Path {
+        global: true,
+        segments: segments.into_iter().map(|s| s.as_ref().into()).collect(),
+    }
+}
+
+pub fn ref_pattern<'a>(
+    name: &Ident,
+    variant: &'a Variant,
+    prefix: &str,
+) -> (Tokens, Vec<BindingInfo<'a>>) {
+    synstructure::match_pattern(
+        &name,
+        &variant.data,
+        &BindOpts::with_prefix(BindStyle::Ref, prefix.to_owned()),
+    )
+}
+
+pub fn trait_parts<'a>(
+    input: &'a DeriveInput,
+    trait_path: &[&str],
+) -> (ImplGenerics<'a>, TyGenerics<'a>, WhereClause) {
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+    let mut where_clause = where_clause.clone();
+    for param in &input.generics.ty_params {
+        where_clause.predicates.push(fmap_trait_where_predicate(
+            Ty::Path(None, param.ident.clone().into()),
+            trait_path,
+            None,
+        ));
+    }
+    (impl_generics, ty_generics, where_clause)
+}
+
+pub fn value<'a>(
+    name: &Ident,
+    variant: &'a Variant,
+    prefix: &str,
+) -> (Tokens, Vec<BindingInfo<'a>>) {
+    synstructure::match_pattern(
+        &name,
+        &variant.data,
+        &BindOpts::with_prefix(BindStyle::Move, prefix.to_owned()),
+    )
+}
+
+pub fn variant_ctor<'a>(
+    input: &'a DeriveInput,
+    variant: &Variant,
+) -> Cow<'a, Ident> {
+    match input.body {
+        Body::Struct(_) => Cow::Borrowed(&input.ident),
+        Body::Enum(_) => {
+            Cow::Owned(Ident::from(
+                format!("{}::{}", input.ident, variant.ident),
+            ))
+        },
+    }
+}
+
+pub fn variants(input: &DeriveInput) -> Cow<[Variant]> {
+    match input.body {
+        Body::Enum(ref variants) => (&**variants).into(),
+        Body::Struct(ref data) => {
+            vec![Variant {
+                ident: input.ident.clone(),
+                attrs: input.attrs.clone(),
+                data: data.clone(),
+                discriminant: None,
+            }].into()
+        },
+    }
+}
+
+pub fn where_predicate(ty: Ty, segments: &[&str]) -> WherePredicate {
+    WherePredicate::BoundPredicate(WhereBoundPredicate {
+        bound_lifetimes: vec![],
+        bounded_ty: ty,
+        bounds: vec![TyParamBound::Trait(
+            PolyTraitRef {
+                bound_lifetimes: vec![],
+                trait_ref: path(segments),
+            },
+            TraitBoundModifier::None,
+        )],
+    })
+}
diff --git a/components/style_derive/compute_squared_distance.rs b/components/style_derive/compute_squared_distance.rs
index 46aa376319d..df02d1312cc 100644
--- a/components/style_derive/compute_squared_distance.rs
+++ b/components/style_derive/compute_squared_distance.rs
@@ -2,50 +2,30 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
-use std::borrow::Cow;
 use syn;
-use synstructure;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(where_predicate(syn::Ty::Path(None, param.ident.clone().into())))
-    }
+    let trait_path = &["values", "distance", "ComputeSquaredDistance"];
+    let (impl_generics, ty_generics, mut where_clause) =
+        cg::trait_parts(&input, trait_path);
 
-    let variants = variants(&input);
+    let variants = cg::variants(&input);
     let mut match_body = quote!();
     match_body.append_all(variants.iter().map(|variant| {
-        let name = match input.body {
-            syn::Body::Struct(_) => Cow::Borrowed(&input.ident),
-            syn::Body::Enum(_) => {
-                Cow::Owned(syn::Ident::from(format!("{}::{}", input.ident, variant.ident)))
-            },
-        };
-        let (this_pattern, this_info) = synstructure::match_pattern(
-            &name,
-            &variant.data,
-            &synstructure::BindOpts::with_prefix(
-                synstructure::BindStyle::Ref,
-                "this".to_owned(),
-            ),
-        );
-        let (other_pattern, other_info) = synstructure::match_pattern(
-            &name,
-            &variant.data,
-            &synstructure::BindOpts::with_prefix(
-                synstructure::BindStyle::Ref,
-                "other".to_owned(),
-            ),
-        );
+        let name = cg::variant_ctor(&input, variant);
+        let (this_pattern, this_info) = cg::ref_pattern(&name, &variant, "this");
+        let (other_pattern, other_info) = cg::ref_pattern(&name, &variant, "other");
         let sum = if this_info.is_empty() {
             quote! { ::values::distance::SquaredDistance::Value(0.) }
         } else {
             let mut sum = quote!();
             sum.append_separated(this_info.iter().zip(&other_info).map(|(this, other)| {
-                where_clause.predicates.push(where_predicate(this.field.ty.clone()));
+                where_clause.predicates.push(
+                    cg::where_predicate(this.field.ty.clone(), trait_path),
+                );
                 quote! {
                     ::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
                 }
@@ -78,40 +58,3 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         }
     }
 }
-
-fn variants(input: &syn::DeriveInput) -> Cow<[syn::Variant]> {
-    match input.body {
-        syn::Body::Enum(ref variants) => (&**variants).into(),
-        syn::Body::Struct(ref data) => {
-            vec![syn::Variant {
-                ident: input.ident.clone(),
-                attrs: input.attrs.clone(),
-                data: data.clone(),
-                discriminant: None,
-            }].into()
-        },
-    }
-}
-
-fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(
-        syn::WhereBoundPredicate {
-            bound_lifetimes: vec![],
-            bounded_ty: ty,
-            bounds: vec![syn::TyParamBound::Trait(
-                syn::PolyTraitRef {
-                    bound_lifetimes: vec![],
-                    trait_ref: syn::Path {
-                        global: true,
-                        segments: vec![
-                            "values".into(),
-                            "distance".into(),
-                            "ComputeSquaredDistance".into(),
-                        ],
-                    },
-                },
-                syn::TraitBoundModifier::None,
-            )],
-        },
-    )
-}
diff --git a/components/style_derive/has_viewport_percentage.rs b/components/style_derive/has_viewport_percentage.rs
index 24e4b919c22..5f26d988b8a 100644
--- a/components/style_derive/has_viewport_percentage.rs
+++ b/components/style_derive/has_viewport_percentage.rs
@@ -2,17 +2,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
 use syn;
 use synstructure;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(where_predicate(syn::Ty::Path(None, param.ident.clone().into())))
-    }
+    let trait_path = &["style_traits", "HasViewportPercentage"];
+    let (impl_generics, ty_generics, mut where_clause) =
+        cg::trait_parts(&input, trait_path);
 
     let style = synstructure::BindStyle::Ref.into();
     let match_body = synstructure::each_variant(&input, &style, |bindings, _| {
@@ -22,7 +21,9 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         };
         let mut expr = quote!(::style_traits::HasViewportPercentage::has_viewport_percentage(#first));
         for binding in rest {
-            where_clause.predicates.push(where_predicate(binding.field.ty.clone()));
+            where_clause.predicates.push(
+                cg::where_predicate(binding.field.ty.clone(), trait_path),
+            );
             expr = quote!(#expr || ::style_traits::HasViewportPercentage::has_viewport_percentage(#binding));
         }
         Some(expr)
@@ -40,17 +41,3 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         }
     }
 }
-
-fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
-        bound_lifetimes: vec![],
-        bounded_ty: ty,
-        bounds: vec![syn::TyParamBound::Trait(
-            syn::PolyTraitRef {
-                bound_lifetimes: vec![],
-                trait_ref: syn::parse_path("::style_traits::HasViewportPercentage").unwrap(),
-            },
-            syn::TraitBoundModifier::None
-        )],
-    })
-}
diff --git a/components/style_derive/lib.rs b/components/style_derive/lib.rs
index a41925ab410..e2b10dc47aa 100644
--- a/components/style_derive/lib.rs
+++ b/components/style_derive/lib.rs
@@ -10,6 +10,7 @@ extern crate synstructure;
 use proc_macro::TokenStream;
 
 mod animate;
+mod cg;
 mod compute_squared_distance;
 mod has_viewport_percentage;
 mod to_animated_value;
diff --git a/components/style_derive/to_animated_value.rs b/components/style_derive/to_animated_value.rs
index ab13a26d5c8..5a66ddf65a4 100644
--- a/components/style_derive/to_animated_value.rs
+++ b/components/style_derive/to_animated_value.rs
@@ -2,49 +2,24 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
 use syn;
-use synstructure;
+use synstructure::BindStyle;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(where_predicate(syn::Ty::Path(None, param.ident.clone().into()), None));
-    }
-
-    let animated_value_type = syn::Path::from(syn::PathSegment {
-        ident: name.clone(),
-        parameters: syn::PathParameters::AngleBracketed(syn::AngleBracketedParameterData {
-            lifetimes: input.generics.lifetimes.iter().map(|l| {
-                l.lifetime.clone()
-            }).collect(),
-            types: input.generics.ty_params.iter().map(|ty| {
-                syn::Ty::Path(
-                    Some(syn::QSelf {
-                        ty: Box::new(syn::Ty::Path(None, ty.ident.clone().into())),
-                        position: 3,
-                    }),
-                    syn::Path {
-                        global: true,
-                        segments: vec![
-                            "values".into(),
-                            "animated".into(),
-                            "ToAnimatedValue".into(),
-                            "AnimatedValue".into(),
-                        ],
-                    },
-                )
-            }).collect(),
-            .. Default::default()
-        }),
-    });
-
-    let to_body = match_body(&input, |field| {
+    let (impl_generics, ty_generics, where_clause, animated_value_type) =
+        cg::fmap_trait_parts(
+            &input,
+            &["values", "animated", "ToAnimatedValue"],
+            "AnimatedValue",
+        );
+
+    let to_body = cg::fmap_match(&input, BindStyle::Move, |field| {
         quote!(::values::animated::ToAnimatedValue::to_animated_value(#field))
     });
-    let from_body = match_body(&input, |field| {
+    let from_body = cg::fmap_match(&input, BindStyle::Move, |field| {
         quote!(::values::animated::ToAnimatedValue::from_animated_value(#field))
     });
 
@@ -69,73 +44,3 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         }
     }
 }
-
-fn match_body<F>(input: &syn::DeriveInput, f: F) -> quote::Tokens
-where
-    F: Fn(&synstructure::BindingInfo) -> quote::Tokens,
-{
-    let by_value = synstructure::BindStyle::Move.into();
-    synstructure::each_variant(&input, &by_value, |fields, variant| {
-        let name = if let syn::Body::Enum(_) = input.body {
-            format!("{}::{}", input.ident, variant.ident).into()
-        } else {
-            variant.ident.clone()
-        };
-        let (animated_value, computed_fields) = synstructure::match_pattern(&name, &variant.data, &by_value);
-        let fields_pairs = fields.iter().zip(computed_fields.iter());
-        let mut computations = quote!();
-        computations.append_all(fields_pairs.map(|(field, computed_field)| {
-            let expr = f(field);
-            quote!(let #computed_field = #expr;)
-        }));
-        Some(quote!(
-            #computations
-            #animated_value
-        ))
-    })
-}
-
-/// `#ty: ::values::animated::ToAnimatedValue<AnimatedValue = #animated_value,>`
-fn where_predicate(ty: syn::Ty, animated_value: Option<syn::Ty>) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
-        bound_lifetimes: vec![],
-        bounded_ty: ty,
-        bounds: vec![syn::TyParamBound::Trait(
-            syn::PolyTraitRef {
-                bound_lifetimes: vec![],
-                trait_ref: trait_ref(animated_value),
-            },
-            syn::TraitBoundModifier::None
-        )],
-    })
-}
-
-/// `::values::animated::ToAnimatedValue<AnimatedValue = #animated_value,>`
-fn trait_ref(animated_value: Option<syn::Ty>) -> syn::Path {
-    syn::Path {
-        global: true,
-        segments: vec![
-            "values".into(),
-            "animated".into(),
-            syn::PathSegment {
-                ident: "ToAnimatedValue".into(),
-                parameters: syn::PathParameters::AngleBracketed(
-                    syn::AngleBracketedParameterData {
-                        bindings: trait_bindings(animated_value),
-                        .. Default::default()
-                    }
-                ),
-            }
-        ],
-    }
-}
-
-/// `AnimatedValue = #animated_value,`
-fn trait_bindings(animated_value: Option<syn::Ty>) -> Vec<syn::TypeBinding> {
-    animated_value.into_iter().map(|ty| {
-        syn::TypeBinding {
-            ident: "AnimatedValue".into(),
-            ty: ty,
-        }
-    }).collect()
-}
diff --git a/components/style_derive/to_animated_zero.rs b/components/style_derive/to_animated_zero.rs
index f44443f4a34..d9e67a8a9fe 100644
--- a/components/style_derive/to_animated_zero.rs
+++ b/components/style_derive/to_animated_zero.rs
@@ -2,78 +2,31 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
 use syn;
-use synstructure;
+use synstructure::BindStyle;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(
-            where_predicate(syn::Ty::Path(None, param.ident.clone().into())),
-        );
-    }
+    let (impl_generics, ty_generics, where_clause) = cg::trait_parts(
+        &input,
+        &["values", "animated", "ToAnimatedZero"],
+    );
 
-    let to_body = match_body(&input);
+    let to_body = cg::fmap_match(&input, BindStyle::Ref, |field| {
+        quote! { ::values::animated::ToAnimatedZero::to_animated_zero(#field)? }
+    });
 
     quote! {
         impl #impl_generics ::values::animated::ToAnimatedZero for #name #ty_generics #where_clause {
             #[allow(unused_variables)]
             #[inline]
             fn to_animated_zero(&self) -> Result<Self, ()> {
-                match *self {
+                Ok(match *self {
                     #to_body
-                }
+                })
             }
         }
     }
 }
-
-fn match_body(input: &syn::DeriveInput) -> quote::Tokens {
-    synstructure::each_variant(&input, &synstructure::BindStyle::Ref.into(), |fields, variant| {
-        let name = if let syn::Body::Enum(_) = input.body {
-            format!("{}::{}", input.ident, variant.ident).into()
-        } else {
-            variant.ident.clone()
-        };
-        let (zero, computed_fields) = synstructure::match_pattern(
-            &name,
-            &variant.data,
-            &synstructure::BindStyle::Move.into(),
-        );
-        let fields_pairs = fields.iter().zip(computed_fields.iter());
-        let mut computations = quote!();
-        computations.append_all(fields_pairs.map(|(field, computed_field)| {
-            quote! {
-                let #computed_field = ::values::animated::ToAnimatedZero::to_animated_zero(#field)?;
-            }
-        }));
-        Some(quote!(
-            #computations
-            Ok(#zero)
-        ))
-    })
-}
-
-fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
-        bound_lifetimes: vec![],
-        bounded_ty: ty,
-        bounds: vec![syn::TyParamBound::Trait(
-            syn::PolyTraitRef {
-                bound_lifetimes: vec![],
-                trait_ref: syn::Path {
-                    global: true,
-                    segments: vec![
-                        "values".into(),
-                        "animated".into(),
-                        "ToAnimatedZero".into(),
-                    ],
-                },
-            },
-            syn::TraitBoundModifier::None,
-        )],
-    })
-}
diff --git a/components/style_derive/to_computed_value.rs b/components/style_derive/to_computed_value.rs
index d7c4801dbf8..967f3320a37 100644
--- a/components/style_derive/to_computed_value.rs
+++ b/components/style_derive/to_computed_value.rs
@@ -2,49 +2,24 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
 use syn;
-use synstructure;
+use synstructure::BindStyle;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(where_predicate(syn::Ty::Path(None, param.ident.clone().into()), None));
-    }
-
-    let computed_value_type = syn::Path::from(syn::PathSegment {
-        ident: name.clone(),
-        parameters: syn::PathParameters::AngleBracketed(syn::AngleBracketedParameterData {
-            lifetimes: input.generics.lifetimes.iter().map(|l| {
-                l.lifetime.clone()
-            }).collect(),
-            types: input.generics.ty_params.iter().map(|ty| {
-                syn::Ty::Path(
-                    Some(syn::QSelf {
-                        ty: Box::new(syn::Ty::Path(None, ty.ident.clone().into())),
-                        position: 3,
-                    }),
-                    syn::Path {
-                        global: true,
-                        segments: vec![
-                            "values".into(),
-                            "computed".into(),
-                            "ToComputedValue".into(),
-                            "ComputedValue".into(),
-                        ],
-                    },
-                )
-            }).collect(),
-            .. Default::default()
-        }),
-    });
-
-    let to_body = match_body(&input, |field| {
+    let (impl_generics, ty_generics, where_clause, computed_value_type) =
+        cg::fmap_trait_parts(
+            &input,
+            &["values", "computed", "ToComputedValue"],
+            "ComputedValue",
+        );
+
+    let to_body = cg::fmap_match(&input, BindStyle::Ref, |field| {
         quote!(::values::computed::ToComputedValue::to_computed_value(#field, context))
     });
-    let from_body = match_body(&input, |field| {
+    let from_body = cg::fmap_match(&input, BindStyle::Ref, |field| {
         quote!(::values::computed::ToComputedValue::from_computed_value(#field))
     });
 
@@ -69,74 +44,3 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         }
     }
 }
-
-fn match_body<F>(input: &syn::DeriveInput, f: F) -> quote::Tokens
-    where F: Fn(&synstructure::BindingInfo) -> quote::Tokens,
-{
-    let by_ref = synstructure::BindStyle::Ref.into();
-    let by_value = synstructure::BindStyle::Move.into();
-
-    synstructure::each_variant(&input, &by_ref, |fields, variant| {
-        let name = if let syn::Body::Enum(_) = input.body {
-            format!("{}::{}", input.ident, variant.ident).into()
-        } else {
-            variant.ident.clone()
-        };
-        let (computed_value, computed_fields) = synstructure::match_pattern(&name, &variant.data, &by_value);
-        let fields_pairs = fields.iter().zip(computed_fields.iter());
-        let mut computations = quote!();
-        computations.append_all(fields_pairs.map(|(field, computed_field)| {
-            let expr = f(field);
-            quote!(let #computed_field = #expr;)
-        }));
-        Some(quote!(
-            #computations
-            #computed_value
-        ))
-    })
-}
-
-/// `#ty: ::values::computed::ToComputedValue<ComputedValue = #computed_value,>`
-fn where_predicate(ty: syn::Ty, computed_value: Option<syn::Ty>) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
-        bound_lifetimes: vec![],
-        bounded_ty: ty,
-        bounds: vec![syn::TyParamBound::Trait(
-            syn::PolyTraitRef {
-                bound_lifetimes: vec![],
-                trait_ref: trait_ref(computed_value),
-            },
-            syn::TraitBoundModifier::None
-        )],
-    })
-}
-
-/// `::values::computed::ToComputedValue<ComputedValue = #computed_value,>`
-fn trait_ref(computed_value: Option<syn::Ty>) -> syn::Path {
-    syn::Path {
-        global: true,
-        segments: vec![
-            "values".into(),
-            "computed".into(),
-            syn::PathSegment {
-                ident: "ToComputedValue".into(),
-                parameters: syn::PathParameters::AngleBracketed(
-                    syn::AngleBracketedParameterData {
-                        bindings: trait_bindings(computed_value),
-                        .. Default::default()
-                    }
-                ),
-            }
-        ],
-    }
-}
-
-/// `ComputedValue = #computed_value,`
-fn trait_bindings(computed_value: Option<syn::Ty>) -> Vec<syn::TypeBinding> {
-    computed_value.into_iter().map(|ty| {
-        syn::TypeBinding {
-            ident: "ComputedValue".into(),
-            ty: ty,
-        }
-    }).collect()
-}
diff --git a/components/style_derive/to_css.rs b/components/style_derive/to_css.rs
index 2dbf8731e45..fbbccb5a493 100644
--- a/components/style_derive/to_css.rs
+++ b/components/style_derive/to_css.rs
@@ -2,17 +2,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cg;
 use quote;
 use syn;
 use synstructure;
 
 pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let name = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    let mut where_clause = where_clause.clone();
-    for param in &input.generics.ty_params {
-        where_clause.predicates.push(where_predicate(syn::Ty::Path(None, param.ident.clone().into())))
-    }
+    let trait_path = &["style_traits", "ToCss"];
+    let (impl_generics, ty_generics, mut where_clause) =
+        cg::trait_parts(&input, trait_path);
 
     let style = synstructure::BindStyle::Ref.into();
     let match_body = synstructure::each_variant(&input, &style, |bindings, variant| {
@@ -61,8 +60,10 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         let mut expr = if !bindings.is_empty() {
             let mut expr = quote! {};
             for binding in bindings {
-                if has_free_params(&binding.field.ty, &input.generics.ty_params) {
-                    where_clause.predicates.push(where_predicate(binding.field.ty.clone()));
+                if cg::is_parameterized(&binding.field.ty, &input.generics.ty_params) {
+                    where_clause.predicates.push(
+                        cg::where_predicate(binding.field.ty.clone(), trait_path),
+                    );
                 }
                 expr = quote! {
                     #expr
@@ -106,49 +107,6 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     }
 }
 
-/// Returns whether `ty` is parameterized by any parameter from `params`.
-fn has_free_params(ty: &syn::Ty, params: &[syn::TyParam]) -> bool {
-    use syn::visit::Visitor;
-
-    struct HasFreeParams<'a> {
-        params: &'a [syn::TyParam],
-        has_free: bool,
-    }
-
-    impl<'a> Visitor for HasFreeParams<'a> {
-        fn visit_path(&mut self, path: &syn::Path) {
-            if !path.global && path.segments.len() == 1 {
-                if self.params.iter().any(|param| param.ident == path.segments[0].ident) {
-                    self.has_free = true;
-                }
-            }
-            syn::visit::walk_path(self, path);
-        }
-    }
-
-    let mut visitor = HasFreeParams { params: params, has_free: false };
-    visitor.visit_ty(ty);
-    visitor.has_free
-}
-
-/// `#ty: ::style_traits::ToCss`
-fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
-    syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
-        bound_lifetimes: vec![],
-        bounded_ty: ty,
-        bounds: vec![syn::TyParamBound::Trait(
-            syn::PolyTraitRef {
-                bound_lifetimes: vec![],
-                trait_ref: syn::Path {
-                    global: true,
-                    segments: vec!["style_traits".into(), "ToCss".into()],
-                },
-            },
-            syn::TraitBoundModifier::None
-        )],
-    })
-}
-
 /// Transforms "FooBar" to "foo-bar".
 ///
 /// If the first Camel segment is "Moz" or "Webkit", the result string