style: Use a computed type for page-size which converts paper sizes to a Size2D

Differential Revision: https://phabricator.services.mozilla.com/D115842

components/style/values/computed/page.rs

@@ -5,10 +5,71 @@
 //! Computed @page at-rule properties
 
 use crate::values::computed::length::NonNegativeLength;
+use crate::values::computed::{Context, ToComputedValue};
 use crate::values::generics;
 use crate::values::generics::size::Size2D;
 
+use crate::values::specified::page as specified;
+pub use generics::page::GenericPageSize;
 pub use generics::page::Orientation;
 pub use generics::page::PaperSize;
+
 /// Computed value of the @page size descriptor
-pub type PageSize = generics::page::GenericPageSize<Size2D<NonNegativeLength>>;
+///
+/// The spec says that the computed value should be the same as the specified
+/// value but with all absolute units, but it's not currently possibly observe
+/// the computed value of page-size.
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss, ToResolvedValue, ToShmem)]
+#[repr(C, u8)]
+pub enum PageSize {
+    /// Specified size, paper size, or paper size and orientation.
+    Size(Size2D<NonNegativeLength>),
+    /// `landscape` or `portrait` value, no specified size.
+    Orientation(Orientation),
+    /// `auto` value
+    Auto,
+}
+
+impl ToComputedValue for specified::PageSize {
+    type ComputedValue = PageSize;
+
+    fn to_computed_value(&self, ctx: &Context) -> Self::ComputedValue {
+        match &*self {
+            Self::Size(s) => PageSize::Size(s.to_computed_value(ctx)),
+            Self::PaperSizeAndOrientation(p, Orientation::Landscape) => PageSize::Size(Size2D {
+                width: p.long_edge().to_computed_value(ctx),
+                height: p.short_edge().to_computed_value(ctx),
+            }),
+            Self::PaperSizeAndOrientation(p, Orientation::Portrait) | Self::PaperSize(p) => {
+                PageSize::Size(Size2D {
+                    width: p.short_edge().to_computed_value(ctx),
+                    height: p.long_edge().to_computed_value(ctx),
+                })
+            },
+            Self::Orientation(o) => PageSize::Orientation(*o),
+            Self::Auto => PageSize::Auto,
+        }
+    }
+
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        match *computed {
+            PageSize::Size(s) => Self::Size(ToComputedValue::from_computed_value(&s)),
+            PageSize::Orientation(o) => Self::Orientation(o),
+            PageSize::Auto => Self::Auto,
+        }
+    }
+}
+
+impl PageSize {
+    /// `auto` value.
+    #[inline]
+    pub fn auto() -> Self {
+        PageSize::Auto
+    }
+
+    /// Whether this is the `auto` value.
+    #[inline]
+    pub fn is_auto(&self) -> bool {
+        matches!(*self, PageSize::Auto)
+    }
+}