Opt out of bounds on type params for #[derive(ComputeSquaredDistance)]

1 files changed, 62 insertions, 33 deletions

diff --git a/components/style_derive/compute_squared_distance.rs b/components/style_derive/compute_squared_distance.rs
index 6254340e358..c978751054d 100644
--- a/components/style_derive/compute_squared_distance.rs
+++ b/components/style_derive/compute_squared_distance.rs
@@ -4,48 +4,67 @@
 
 use animate::AnimationVariantAttrs;
 use cg;
+use darling::util::IdentList;
 use quote::Tokens;
 use syn::{DeriveInput, Path};
 use synstructure;
 
-pub fn derive(input: DeriveInput) -> Tokens {
-    let name = &input.ident;
-    let trait_path = parse_quote!(values::distance::ComputeSquaredDistance);
-    let (impl_generics, ty_generics, mut where_clause) =
-        cg::trait_parts(&input, &trait_path);
-
+pub fn derive(mut input: DeriveInput) -> Tokens {
     let input_attrs = cg::parse_input_attrs::<DistanceInputAttrs>(&input);
-    let s = synstructure::Structure::new(&input);
-    let mut append_error_clause = s.variants().len() > 1;
-
-    let mut match_body = s.variants().iter().fold(quote!(), |body, variant| {
-        let attrs = cg::parse_variant_attrs::<AnimationVariantAttrs>(&variant.ast());
-        if attrs.error {
-            append_error_clause = true;
-            return body;
+    let no_bound = input_attrs.no_bound.unwrap_or_default();
+    let mut where_clause = input.generics.where_clause.take();
+    for param in input.generics.type_params() {
+        if !no_bound.contains(&param.ident) {
+            cg::add_predicate(
+                &mut where_clause,
+                parse_quote!(#param: ::values::distance::ComputeSquaredDistance),
+            );
         }
+    }
 
-        let (this_pattern, this_info) = cg::ref_pattern(&variant, "this");
-        let (other_pattern, other_info) = cg::ref_pattern(&variant, "other");
-        let sum = if this_info.is_empty() {
-            quote! { ::values::distance::SquaredDistance::from_sqrt(0.) }
-        } else {
-            let mut sum = quote!();
-            sum.append_separated(this_info.iter().zip(&other_info).map(|(this, other)| {
-                where_clause.add_trait_bound(&this.ast().ty);
-                quote! {
-                    ::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
+    let (mut match_body, append_error_clause) = {
+        let s = synstructure::Structure::new(&input);
+        let mut append_error_clause = s.variants().len() > 1;
+
+        let match_body = s.variants().iter().fold(quote!(), |body, variant| {
+            let attrs = cg::parse_variant_attrs::<AnimationVariantAttrs>(&variant.ast());
+            if attrs.error {
+                append_error_clause = true;
+                return body;
+            }
+
+            let (this_pattern, this_info) = cg::ref_pattern(&variant, "this");
+            let (other_pattern, other_info) = cg::ref_pattern(&variant, "other");
+            let sum = if this_info.is_empty() {
+                quote! { ::values::distance::SquaredDistance::from_sqrt(0.) }
+            } else {
+                let mut sum = quote!();
+                sum.append_separated(this_info.iter().zip(&other_info).map(|(this, other)| {
+                    let field_attrs = cg::parse_field_attrs::<DistanceFieldAttrs>(&this.ast());
+                    if field_attrs.field_bound {
+                        let ty = &this.ast().ty;
+                        cg::add_predicate(
+                            &mut where_clause,
+                            parse_quote!(#ty: ::values::distance::ComputeSquaredDistance),
+                        );
+                    }
+                    quote! {
+                        ::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
+                    }
+                }), quote!(+));
+                sum
+            };
+            quote! {
+                #body
+                (&#this_pattern, &#other_pattern) => {
+                    Ok(#sum)
                 }
-            }), quote!(+));
-            sum
-        };
-        quote! {
-            #body
-            (&#this_pattern, &#other_pattern) => {
-                Ok(#sum)
             }
-        }
-    });
+        });
+
+        (match_body, append_error_clause)
+    };
+    input.generics.where_clause = where_clause;
 
     if append_error_clause {
         if let Some(fallback) = input_attrs.fallback {
@@ -57,6 +76,9 @@ pub fn derive(input: DeriveInput) -> Tokens {
         }
     }
 
+    let name = &input.ident;
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
     quote! {
         impl #impl_generics ::values::distance::ComputeSquaredDistance for #name #ty_generics #where_clause {
             #[allow(unused_variables, unused_imports)]
@@ -77,4 +99,11 @@ pub fn derive(input: DeriveInput) -> Tokens {
 #[derive(Default, FromDeriveInput)]
 struct DistanceInputAttrs {
     fallback: Option<Path>,
+    no_bound: Option<IdentList>,
+}
+
+#[darling(attributes(distance), default)]
+#[derive(Default, FromField)]
+struct DistanceFieldAttrs {
+    field_bound: bool,
 }