style: Part 2 - Add page-size attribute to nsStyleStruct and property parsing

This parsing is hidden behind the pref layout.css.page-size.enabled.

It isn't ideal that we parse this as a property, but we can't treat it as a
descriptor because of compatibility issues with other browsers. There are also
outstanding spec issues related to how descriptors like page-size are cascaded,
and whether the !important specifier is valid or not.

Differential Revision: https://phabricator.services.mozilla.com/D103958

components/style/properties/build.py

@@ -37,6 +37,7 @@ STYLE_STRUCT_LIST = [
     "list",
     "margin",
     "outline",
+    "page",
     "padding",
     "position",
     "svg",

components/style/properties/counted_unknown_properties.py

@@ -19,7 +19,6 @@ COUNTED_UNKNOWN_PROPERTIES = [
     "text-size-adjust",
     "-webkit-font-feature-settings",
     "-webkit-user-drag",
-    "size",
     "-webkit-clip-path",
     "orphans",
     "widows",

components/style/properties/gecko.mako.rs

@@ -781,6 +781,9 @@ fn static_assert() {
     % endfor
 </%self:impl_trait>
 
+<%self:impl_trait style_struct_name="Page">
+</%self:impl_trait>
+
 <% skip_position_longhands = " ".join(x.ident for x in SIDES) %>
 <%self:impl_trait style_struct_name="Position"
                   skip_longhands="${skip_position_longhands}

components/style/properties/longhands/page.mako.rs

@@ -0,0 +1,21 @@
+/* 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/. */
+
+<%namespace name="helpers" file="/helpers.mako.rs" />
+<% from data import PAGE_RULE %>
+
+<% data.new_style_struct("Page", inherited=False) %>
+
+${helpers.predefined_type(
+    "size",
+    "PageSize",
+    "computed::PageSize::auto()",
+    engines="gecko",
+    gecko_pref="layout.css.page-size.enabled",
+    initial_specified_value="specified::PageSize::auto()",
+    spec="https://drafts.csswg.org/css-page-3/#page-size-prop",
+    boxed=True,
+    animation_value_type="none",
+    rule_types_allowed=PAGE_RULE,
+)}

components/style/values/computed/page.rs

@@ -11,4 +11,4 @@ use crate::values::generics::size::Size2D;
 pub use generics::page::Orientation;
 pub use generics::page::PaperSize;
 /// Computed value of the @page size descriptor
-pub type PageSize = generics::page::PageSize<Size2D<NonNegativeLength>>;
+pub type PageSize = generics::page::GenericPageSize<Size2D<NonNegativeLength>>;

components/style/values/generics/page.rs

@@ -86,7 +86,7 @@ pub enum Orientation {
     ToShmem,
 )]
 #[repr(C, u8)]
-pub enum PageSize<S> {
+pub enum GenericPageSize<S> {
     /// Page dimensions.
     Size(S),
     /// Paper size with no orientation.
@@ -99,6 +99,8 @@ pub enum PageSize<S> {
     Auto,
 }
 
+pub use self::GenericPageSize as PageSize;
+
 impl<S> PageSize<S> {
     /// `auto` value.
     #[inline]