Bug 1542178 - Add derive code for a new ToResolvedValue trait, and a few trivial implementations. r=heycam

Differential Revision: https://phabricator.services.mozilla.com/D26782

servo/components/style/values/resolved/mod.rs

@@ -0,0 +1,208 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! Resolved values. These are almost always computed values, but in some cases
+//! there are used values.
+
+use cssparser;
+use smallvec::SmallVec;
+use crate::properties::ComputedValues;
+use crate::values::computed;
+
+/// Information needed to resolve a given value.
+pub struct Context<'a> {
+    /// The style we're resolving for. This is useful to resolve currentColor.
+    pub style: &'a ComputedValues,
+    // TODO(emilio): Add layout box information, and maybe property-specific
+    // information?
+}
+
+/// A trait to represent the conversion between resolved and resolved values.
+///
+/// This trait is derivable with `#[derive(ToResolvedValue)]`.
+///
+/// The deriving code assumes that if the type isn't generic, then the trait can
+/// be implemented as simple move. This means that a manual implementation with
+/// `ResolvedValue = Self` is bogus if it returns anything else than a clone.
+pub trait ToResolvedValue {
+    /// The resolved value type we're going to be converted to.
+    type ResolvedValue;
+
+    /// Convert a resolved value to a resolved value.
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue;
+
+    /// Convert a resolved value to resolved value form.
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self;
+}
+
+macro_rules! trivial_to_resolved_value {
+    ($ty:ty) => {
+        impl $crate::values::resolved::ToResolvedValue for $ty {
+            type ResolvedValue = Self;
+
+            #[inline]
+            fn to_resolved_value(self, _: &Context) -> Self {
+                self
+            }
+
+            #[inline]
+            fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+                resolved
+            }
+        }
+    };
+}
+
+trivial_to_resolved_value!(());
+trivial_to_resolved_value!(bool);
+trivial_to_resolved_value!(f32);
+trivial_to_resolved_value!(i32);
+trivial_to_resolved_value!(u8);
+trivial_to_resolved_value!(i8);
+trivial_to_resolved_value!(u16);
+trivial_to_resolved_value!(u32);
+#[cfg(feature = "servo")]
+trivial_to_resolved_value!(Prefix);
+trivial_to_resolved_value!(String);
+trivial_to_resolved_value!(Box<str>);
+trivial_to_resolved_value!(cssparser::RGBA);
+trivial_to_resolved_value!(crate::Atom);
+trivial_to_resolved_value!(app_units::Au);
+trivial_to_resolved_value!(computed::url::ComputedUrl);
+trivial_to_resolved_value!(computed::url::ComputedImageUrl);
+
+impl<A, B> ToResolvedValue for (A, B)
+where
+    A: ToResolvedValue,
+    B: ToResolvedValue,
+{
+    type ResolvedValue = (
+        <A as ToResolvedValue>::ResolvedValue,
+        <B as ToResolvedValue>::ResolvedValue,
+    );
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        (
+            self.0.to_resolved_value(context),
+            self.1.to_resolved_value(context),
+        )
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        (
+            A::from_resolved_value(resolved.0),
+            B::from_resolved_value(resolved.1),
+        )
+    }
+}
+
+impl<T> ToResolvedValue for Option<T>
+where
+    T: ToResolvedValue,
+{
+    type ResolvedValue = Option<<T as ToResolvedValue>::ResolvedValue>;
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        self.map(|item| item.to_resolved_value(context))
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        resolved.map(T::from_resolved_value)
+    }
+}
+
+impl<T> ToResolvedValue for SmallVec<[T; 1]>
+where
+    T: ToResolvedValue,
+{
+    type ResolvedValue = SmallVec<[<T as ToResolvedValue>::ResolvedValue; 1]>;
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        self.into_iter()
+            .map(|item| item.to_resolved_value(context))
+            .collect()
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        resolved.into_iter().map(T::from_resolved_value).collect()
+    }
+}
+
+impl<T> ToResolvedValue for Vec<T>
+where
+    T: ToResolvedValue,
+{
+    type ResolvedValue = Vec<<T as ToResolvedValue>::ResolvedValue>;
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        self.into_iter()
+            .map(|item| item.to_resolved_value(context))
+            .collect()
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        resolved.into_iter().map(T::from_resolved_value).collect()
+    }
+}
+
+impl<T> ToResolvedValue for Box<T>
+where
+    T: ToResolvedValue,
+{
+    type ResolvedValue = Box<<T as ToResolvedValue>::ResolvedValue>;
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        Box::new(T::to_resolved_value(*self, context))
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        Box::new(T::from_resolved_value(*resolved))
+    }
+}
+
+impl<T> ToResolvedValue for Box<[T]>
+where
+    T: ToResolvedValue,
+{
+    type ResolvedValue = Box<[<T as ToResolvedValue>::ResolvedValue]>;
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        Vec::from(self).to_resolved_value(context).into_boxed_slice()
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        Vec::from_resolved_value(Vec::from(resolved)).into_boxed_slice()
+    }
+}
+
+
+/// A resolved color value is an rgba color, with currentcolor resolved.
+pub type Color = cssparser::RGBA;
+
+impl ToResolvedValue for computed::Color {
+    type ResolvedValue = Color;
+
+    #[inline]
+    fn to_resolved_value(self, context: &Context) -> Self::ResolvedValue {
+        context.style.resolve_color(self)
+    }
+
+    #[inline]
+    fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+        use crate::values::generics::color::Color as GenericColor;
+        GenericColor::Numeric(resolved)
+    }
+}

servo/components/style_derive/to_resolved_value.rs

@@ -0,0 +1,69 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use derive_common::cg;
+use proc_macro2::TokenStream;
+use syn::DeriveInput;
+use synstructure::BindStyle;
+use to_computed_value;
+
+pub fn derive(input: DeriveInput) -> TokenStream {
+    let trait_impl = |from_body, to_body| {
+        quote! {
+            #[inline]
+            fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+                match resolved {
+                    #from_body
+                }
+            }
+
+            #[inline]
+            fn to_resolved_value(
+                self,
+                context: &crate::values::resolved::Context,
+            ) -> Self::ResolvedValue {
+                match self {
+                    #to_body
+                }
+            }
+       }
+    };
+
+    let non_generic_implementation = || {
+        Some(quote! {
+            type ResolvedValue = Self;
+
+            #[inline]
+            fn from_resolved_value(resolved: Self::ResolvedValue) -> Self {
+                resolved
+            }
+
+            #[inline]
+            fn to_resolved_value(
+                self,
+                context: &crate::values::resolved::Context,
+            ) -> Self {
+                self
+            }
+        })
+    };
+
+    to_computed_value::derive_to_value(
+        input,
+        parse_quote!(crate::values::resolved::ToResolvedValue),
+        parse_quote!(ResolvedValue),
+        BindStyle::Move,
+        |binding| cg::parse_field_attrs::<ResolvedValueAttrs>(&binding.ast()).field_bound,
+        |binding| quote!(crate::values::resolved::ToResolvedValue::from_resolved_value(#binding)),
+        |binding| quote!(crate::values::resolved::ToResolvedValue::to_resolved_value(#binding, context)),
+        trait_impl,
+        non_generic_implementation,
+    )
+}
+
+#[darling(attributes(resolve), default)]
+#[derive(Default, FromField)]
+struct ResolvedValueAttrs {
+    field_bound: bool,
+}