style: Support break-inside: avoid-{page,column}

break-before/after: page|column seem harder because you need to deal
with nested breaks, I think, but this should be straight-forward.

Differential Revision: https://phabricator.services.mozilla.com/D121206

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

@@ -503,7 +503,6 @@ ${helpers.predefined_type(
     "BreakWithin",
     "computed::BreakWithin::Auto",
     engines="gecko",
-    aliases="page-break-inside",
     spec="https://drafts.csswg.org/css-break/#propdef-break-inside",
     animation_value_type="discrete",
 )}

components/style/properties/shorthands/box.mako.rs

@@ -316,15 +316,15 @@ ${helpers.two_properties_shorthand(
     name="page-break-before"
     flags="SHORTHAND_IN_GETCS IS_LEGACY_SHORTHAND"
     sub_properties="break-before"
-    spec="https://drafts.csswg.org/css2/page.html#propdef-page-break-before"
+    spec="https://drafts.csswg.org/css-break-3/#page-break-properties"
 >
     pub fn parse_value<'i>(
-        _: &ParserContext,
+        context: &ParserContext,
         input: &mut Parser<'i, '_>,
     ) -> Result<Longhands, ParseError<'i>> {
         use crate::values::specified::box_::BreakBetween;
         Ok(expanded! {
-            break_before: BreakBetween::parse_legacy(input)?,
+            break_before: BreakBetween::parse_legacy(context, input)?,
         })
     }
 
@@ -340,15 +340,15 @@ ${helpers.two_properties_shorthand(
     name="page-break-after"
     flags="SHORTHAND_IN_GETCS IS_LEGACY_SHORTHAND"
     sub_properties="break-after"
-    spec="https://drafts.csswg.org/css2/page.html#propdef-page-break-after"
+    spec="https://drafts.csswg.org/css-break-3/#page-break-properties"
 >
     pub fn parse_value<'i>(
-        _: &ParserContext,
+        context: &ParserContext,
         input: &mut Parser<'i, '_>,
     ) -> Result<Longhands, ParseError<'i>> {
         use crate::values::specified::box_::BreakBetween;
         Ok(expanded! {
-            break_after: BreakBetween::parse_legacy(input)?,
+            break_after: BreakBetween::parse_legacy(context, input)?,
         })
     }
 
@@ -359,6 +359,30 @@ ${helpers.two_properties_shorthand(
     }
 </%helpers:shorthand>
 
+<%helpers:shorthand
+    engines="gecko"
+    name="page-break-inside"
+    flags="SHORTHAND_IN_GETCS IS_LEGACY_SHORTHAND"
+    sub_properties="break-inside"
+    spec="https://drafts.csswg.org/css-break-3/#page-break-properties"
+>
+    pub fn parse_value<'i>(
+        context: &ParserContext,
+        input: &mut Parser<'i, '_>,
+    ) -> Result<Longhands, ParseError<'i>> {
+        use crate::values::specified::box_::BreakWithin;
+        Ok(expanded! {
+            break_inside: BreakWithin::parse_legacy(context, input)?,
+        })
+    }
+
+    impl<'a> ToCss for LonghandsToSerialize<'a> {
+        fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result where W: fmt::Write {
+            self.break_inside.to_css_legacy(dest)
+        }
+    }
+</%helpers:shorthand>
+
 <%helpers:shorthand name="offset"
                     engines="gecko"
                     sub_properties="offset-path offset-distance offset-rotate offset-anchor"

components/style/values/specified/box.rs

@@ -1894,28 +1894,19 @@ pub enum BreakBetween {
 }
 
 impl BreakBetween {
-    /// Parse a legacy break-between value for `page-break-*`.
+    /// Parse a legacy break-between value for `page-break-{before,after}`.
     ///
     /// See https://drafts.csswg.org/css-break/#page-break-properties.
     #[inline]
-    pub fn parse_legacy<'i>(input: &mut Parser<'i, '_>) -> Result<Self, ParseError<'i>> {
-        let location = input.current_source_location();
-        let ident = input.expect_ident()?;
-        let break_value = match BreakBetween::from_ident(ident) {
-            Ok(v) => v,
-            Err(()) => {
-                return Err(location
-                    .new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone())));
-            },
-        };
+    pub(crate) fn parse_legacy<'i>(_: &ParserContext, input: &mut Parser<'i, '_>) -> Result<Self, ParseError<'i>> {
+        let break_value = BreakBetween::parse(input)?;
         match break_value {
             BreakBetween::Always => Ok(BreakBetween::Page),
             BreakBetween::Auto | BreakBetween::Avoid | BreakBetween::Left | BreakBetween::Right => {
                 Ok(break_value)
             },
             BreakBetween::Page => {
-                Err(location
-                    .new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone())))
+                Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
             },
         }
     }
@@ -1923,7 +1914,7 @@ impl BreakBetween {
     /// Serialize a legacy break-between value for `page-break-*`.
     ///
     /// See https://drafts.csswg.org/css-break/#page-break-properties.
-    pub fn to_css_legacy<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    pub(crate) fn to_css_legacy<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
         W: Write,
     {
@@ -1960,6 +1951,37 @@ impl BreakBetween {
 pub enum BreakWithin {
     Auto,
     Avoid,
+    AvoidPage,
+    AvoidColumn,
+}
+
+impl BreakWithin {
+    /// Parse a legacy break-between value for `page-break-inside`.
+    ///
+    /// See https://drafts.csswg.org/css-break/#page-break-properties.
+    #[inline]
+    pub(crate) fn parse_legacy<'i>(_: &ParserContext, input: &mut Parser<'i, '_>) -> Result<Self, ParseError<'i>> {
+        let break_value = BreakWithin::parse(input)?;
+        match break_value {
+            BreakWithin::Auto | BreakWithin::Avoid => Ok(break_value),
+            BreakWithin::AvoidPage | BreakWithin::AvoidColumn => {
+                Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+            },
+        }
+    }
+
+    /// Serialize a legacy break-between value for `page-break-inside`.
+    ///
+    /// See https://drafts.csswg.org/css-break/#page-break-properties.
+    pub(crate) fn to_css_legacy<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        match *self {
+            BreakWithin::Auto | BreakWithin::Avoid => self.to_css(dest),
+            BreakWithin::AvoidPage | BreakWithin::AvoidColumn => Ok(()),
+        }
+    }
 }
 
 /// The value for the `overflow-x` / `overflow-y` properties.