style: Merge ImageLayer and Image.

ImageLayer is almost the only usage of Image, so keeping them in the same enum
makes the resulting C++ struct smaller, and makes it map more cleanly to
nsStyleImage.

Differential Revision: https://phabricator.services.mozilla.com/D62161

components/style/values/generics/image.rs

@@ -13,51 +13,22 @@ use servo_arc::Arc;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
-/// An <image> | <none> (for background-image, for example).
-#[derive(
-    Clone,
-    Debug,
-    MallocSizeOf,
-    Parse,
-    PartialEq,
-    SpecifiedValueInfo,
-    ToComputedValue,
-    ToCss,
-    ToResolvedValue,
-    ToShmem,
-)]
-pub enum GenericImageLayer<Image> {
-    /// The `none` value.
-    None,
-    /// The `<image>` value.
-    Image(Image),
-}
-
-pub use self::GenericImageLayer as ImageLayer;
-
-impl<I> ImageLayer<I> {
-    /// Returns `none`.
-    #[inline]
-    pub fn none() -> Self {
-        ImageLayer::None
-    }
-}
-
-/// An [image].
+/// An `<image> | none` value.
 ///
-/// [image]: https://drafts.csswg.org/css-images/#image-values
+/// https://drafts.csswg.org/css-images/#image-values
 #[derive(
     Clone, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToResolvedValue, ToShmem,
 )]
 #[repr(C, u8)]
-pub enum GenericImage<Gradient, MozImageRect, ImageUrl> {
+pub enum GenericImage<G, MozImageRect, ImageUrl> {
+    /// `none` variant.
+    None,
     /// A `<url()>` image.
     Url(ImageUrl),
 
     /// A `<gradient>` image.  Gradients are rather large, and not nearly as
     /// common as urls, so we box them here to keep the size of this enum sane.
-    Gradient(Box<Gradient>),
-
+    Gradient(Box<G>),
     /// A `-moz-image-rect` image.  Also fairly large and rare.
     // not cfg’ed out on non-Gecko to avoid `error[E0392]: parameter `MozImageRect` is never used`
     // Instead we make MozImageRect an empty enum
@@ -285,7 +256,7 @@ impl ToCss for PaintWorklet {
 ///
 /// `-moz-image-rect(<uri>, top, right, bottom, left);`
 #[allow(missing_docs)]
-#[css(comma, function)]
+#[css(comma, function = "-moz-image-rect")]
 #[derive(
     Clone,
     Debug,
@@ -297,7 +268,8 @@ impl ToCss for PaintWorklet {
     ToResolvedValue,
     ToShmem,
 )]
-pub struct MozImageRect<NumberOrPercentage, MozImageRectUrl> {
+#[repr(C)]
+pub struct GenericMozImageRect<NumberOrPercentage, MozImageRectUrl> {
     pub url: MozImageRectUrl,
     pub top: NumberOrPercentage,
     pub right: NumberOrPercentage,
@@ -305,6 +277,8 @@ pub struct MozImageRect<NumberOrPercentage, MozImageRectUrl> {
     pub left: NumberOrPercentage,
 }
 
+pub use self::GenericMozImageRect as MozImageRect;
+
 impl<G, R, U> fmt::Debug for Image<G, R, U>
 where
     G: ToCss,
@@ -327,6 +301,7 @@ where
         W: Write,
     {
         match *self {
+            Image::None => dest.write_str("none"),
             Image::Url(ref url) => url.to_css(dest),
             Image::Gradient(ref gradient) => gradient.to_css(dest),
             Image::Rect(ref rect) => rect.to_css(dest),