style: Don't allow fallback alignment in place-content shorthand.

Bug: 1430622
Reviewed-by: xidorn,mats
MozReview-Commit-ID: sALBFJeqvr

components/style/properties/shorthand/position.mako.rs

@@ -611,17 +611,19 @@
 <%helpers:shorthand name="place-content" sub_properties="align-content justify-content"
                     spec="https://drafts.csswg.org/css-align/#propdef-place-content"
                     products="gecko">
-    use properties::longhands::align_content;
-    use properties::longhands::justify_content;
+    use values::specified::align::{AlignJustifyContent, FallbackAllowed};
 
-    pub fn parse_value<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
-                               -> Result<Longhands, ParseError<'i>> {
-        let align = align_content::parse(context, input)?;
+    pub fn parse_value<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Longhands, ParseError<'i>> {
+        let align = AlignJustifyContent::parse_with_fallback(input, FallbackAllowed::No)?;
         if align.has_extra_flags() {
             return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
         }
-        let justify = input.try(|input| justify_content::parse(context, input))
-                           .unwrap_or(justify_content::SpecifiedValue::from(align));
+        let justify =
+            input.try(|input| AlignJustifyContent::parse_with_fallback(input, FallbackAllowed::No))
+                .unwrap_or(align);
         if justify.has_extra_flags() {
             return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
         }

components/style/values/specified/align.rs

@@ -119,6 +119,21 @@ const ALIGN_ALL_SHIFT: u32 = structs::NS_STYLE_ALIGN_ALL_SHIFT;
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub struct AlignJustifyContent(u16);
 
+/// Whether fallback is allowed in align-content / justify-content parsing.
+///
+/// This is used for the place-content shorthand, until the resolutions from [1]
+/// are specified.
+///
+/// [1]: https://github.com/w3c/csswg-drafts/issues/1002
+#[derive(Clone, Copy, PartialEq)]
+pub enum FallbackAllowed {
+    /// Allow fallback alignment.
+    Yes,
+    /// Don't allow fallback alignment.
+    No,
+}
+
+
 impl AlignJustifyContent {
     /// The initial value 'normal'
     #[inline]
@@ -159,6 +174,38 @@ impl AlignJustifyContent {
     pub fn has_extra_flags(self) -> bool {
         self.primary().intersects(AlignFlags::FLAG_BITS) || self.fallback().intersects(AlignFlags::FLAG_BITS)
     }
+
+    /// Parse a value for align-content / justify-content, optionally allowing
+    /// fallback.
+    pub fn parse_with_fallback<'i, 't>(
+        input: &mut Parser<'i, 't>,
+        fallback_allowed: FallbackAllowed,
+    ) -> Result<Self, ParseError<'i>> {
+        // normal | <baseline-position>
+        if let Ok(value) = input.try(|input| parse_normal_or_baseline(input)) {
+            return Ok(AlignJustifyContent::new(value))
+        }
+
+        // <content-distribution> followed by optional <*-position>
+        if let Ok(value) = input.try(|input| parse_content_distribution(input)) {
+            if fallback_allowed == FallbackAllowed::Yes {
+                if let Ok(fallback) = input.try(|input| parse_overflow_content_position(input)) {
+                    return Ok(AlignJustifyContent::with_fallback(value, fallback))
+                }
+            }
+            return Ok(AlignJustifyContent::new(value))
+        }
+
+        // <*-position> followed by optional <content-distribution>
+        let fallback = parse_overflow_content_position(input)?;
+        if fallback_allowed == FallbackAllowed::Yes {
+            if let Ok(value) = input.try(|input| parse_content_distribution(input)) {
+                return Ok(AlignJustifyContent::with_fallback(value, fallback))
+            }
+        }
+
+        Ok(AlignJustifyContent::new(fallback))
+    }
 }
 
 impl ToCss for AlignJustifyContent {
@@ -180,27 +227,7 @@ impl Parse for AlignJustifyContent {
     // normal | <baseline-position> |
     // [ <content-distribution> || [ <overflow-position>? && <content-position> ] ]
     fn parse<'i, 't>(_: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
-        // normal | <baseline-position>
-        if let Ok(value) = input.try(|input| parse_normal_or_baseline(input)) {
-            return Ok(AlignJustifyContent::new(value))
-        }
-
-        // <content-distribution> followed by optional <*-position>
-        if let Ok(value) = input.try(|input| parse_content_distribution(input)) {
-            if let Ok(fallback) = input.try(|input| parse_overflow_content_position(input)) {
-                return Ok(AlignJustifyContent::with_fallback(value, fallback))
-            }
-            return Ok(AlignJustifyContent::new(value))
-        }
-
-        // <*-position> followed by optional <content-distribution>
-        if let Ok(fallback) = input.try(|input| parse_overflow_content_position(input)) {
-            if let Ok(value) = input.try(|input| parse_content_distribution(input)) {
-                return Ok(AlignJustifyContent::with_fallback(value, fallback))
-            }
-            return Ok(AlignJustifyContent::new(fallback))
-        }
-        Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+        Self::parse_with_fallback(input, FallbackAllowed::Yes)
     }
 }