style: Support calc in cursor.

Bug: 1453258
Reviewed-by: emilio
MozReview-Commit-ID: 1ZzxkYboWZg

components/style/values/generics/pointing.rs

@@ -4,6 +4,10 @@
 
 //! Generic values for pointing properties.
 
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ToCss};
+use style_traits::cursor::CursorKind;
+
 /// A generic value for the `caret-color` property.
 #[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
          ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
@@ -13,3 +17,63 @@ pub enum CaretColor<Color> {
     /// The keyword `auto`.
     Auto,
 }
+
+/// A generic value for the `cursor` property.
+///
+/// https://drafts.csswg.org/css-ui/#cursor
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+pub struct Cursor<Image> {
+    /// The parsed images for the cursor.
+    pub images: Box<[Image]>,
+    /// The kind of the cursor [default | help | ...].
+    pub keyword: CursorKind,
+}
+
+impl<Image> Cursor<Image> {
+    /// Set `cursor` to `auto`
+    #[inline]
+    pub fn auto() -> Self {
+        Self {
+            images: vec![].into_boxed_slice(),
+            keyword: CursorKind::Auto,
+        }
+    }
+}
+
+impl<Image: ToCss> ToCss for Cursor<Image> {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        for image in &*self.images {
+            image.to_css(dest)?;
+            dest.write_str(", ")?;
+        }
+        self.keyword.to_css(dest)
+    }
+}
+
+/// A generic value for item of `image cursors`.
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+pub struct CursorImage<ImageUrl, Number> {
+    /// The url to parse images from.
+    pub url: ImageUrl,
+    /// The <x> and <y> coordinates.
+    pub hotspot: Option<(Number, Number)>,
+}
+
+impl<ImageUrl: ToCss, Number: ToCss> ToCss for CursorImage<ImageUrl, Number> {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        self.url.to_css(dest)?;
+        if let Some((ref x, ref y)) = self.hotspot {
+            dest.write_str(" ")?;
+            x.to_css(dest)?;
+            dest.write_str(" ")?;
+            y.to_css(dest)?;
+        }
+        Ok(())
+    }
+}