style: Reduce code size of shorthand serialization

Differential Revision: https://phabricator.services.mozilla.com/D118835

components/style/properties/declaration_block.rs

@@ -1197,7 +1197,7 @@ pub fn append_declaration_value<'a, 'b: 'a>(
         AppendableValue::Css(css) => dest.write_str(css),
         AppendableValue::Declaration(decl) => decl.to_css(dest),
         AppendableValue::DeclarationsForShorthand(shorthand, decls) => {
-            shorthand.longhands_to_css(decls, &mut CssWriter::new(dest))
+            shorthand.longhands_to_css(decls, dest)
         },
     }
 }

components/style/properties/helpers.mako.rs

@@ -845,10 +845,7 @@
         impl<'a> LonghandsToSerialize<'a> {
             /// Tries to get a serializable set of longhands given a set of
             /// property declarations.
-            pub fn from_iter<I>(iter: I) -> Result<Self, ()>
-            where
-                I: Iterator<Item=&'a PropertyDeclaration>,
-            {
+            pub fn from_iter(iter: impl Iterator<Item = &'a PropertyDeclaration>) -> Result<Self, ()> {
                 // Define all of the expected variables that correspond to the shorthand
                 % for sub_property in shorthand.sub_properties:
                     let mut ${sub_property.ident} =
@@ -856,8 +853,8 @@
                 % endfor
 
                 // Attempt to assign the incoming declarations to the expected variables
-                for longhand in iter {
-                    match *longhand {
+                for declaration in iter {
+                    match *declaration {
                         % for sub_property in shorthand.sub_properties:
                             PropertyDeclaration::${sub_property.camel_case}(ref value) => {
                                 ${sub_property.ident} = Some(value)
@@ -918,6 +915,14 @@
             })
         }
 
+        /// Try to serialize a given shorthand to a string.
+        pub fn to_css(declarations: &[&PropertyDeclaration], dest: &mut crate::str::CssStringWriter) -> fmt::Result {
+            match LonghandsToSerialize::from_iter(declarations.iter().cloned()) {
+                Ok(longhands) => longhands.to_css(&mut CssWriter::new(dest)),
+                Err(_) => Ok(())
+            }
+        }
+
         ${caller.body()}
     }
     % endif

components/style/properties/properties.mako.rs

@@ -1471,34 +1471,31 @@ impl ShorthandId {
     ///
     /// Returns an error if writing to the stream fails, or if the declarations
     /// do not map to a shorthand.
-    pub fn longhands_to_css<W>(
+    pub fn longhands_to_css(
         &self,
         declarations: &[&PropertyDeclaration],
-        dest: &mut CssWriter<W>,
-    ) -> fmt::Result
-    where
-        W: Write,
-    {
-        // TODO(emilio): Save codesize here by using a lookup table on
-        // ShorthandId instead.
-        let declarations = declarations.iter().cloned();
-        match *self {
-            ShorthandId::All => {
-                // No need to try to serialize the declarations as the 'all'
-                // shorthand, since it only accepts CSS-wide keywords (and
-                // variable references), which will be handled in
-                // get_shorthand_appendable_value.
-                Ok(())
-            }
-            % for property in data.shorthands_except_all():
-                ShorthandId::${property.camel_case} => {
-                    match shorthands::${property.ident}::LonghandsToSerialize::from_iter(declarations) {
-                        Ok(longhands) => longhands.to_css(dest),
-                        Err(_) => Ok(())
-                    }
-                },
-            % endfor
+        dest: &mut CssStringWriter,
+    ) -> fmt::Result {
+        type LonghandsToCssFn = for<'a, 'b> fn(&'a [&'b PropertyDeclaration], &mut CssStringWriter) -> fmt::Result;
+        fn all_to_css(_: &[&PropertyDeclaration], _: &mut CssStringWriter) -> fmt::Result {
+            // No need to try to serialize the declarations as the 'all'
+            // shorthand, since it only accepts CSS-wide keywords (and variable
+            // references), which will be handled in
+            // get_shorthand_appendable_value.
+            Ok(())
         }
+
+        static LONGHANDS_TO_CSS: [LonghandsToCssFn; ${len(data.shorthands)}] = [
+            % for shorthand in data.shorthands:
+            % if shorthand.ident == "all":
+                all_to_css,
+            % else:
+                shorthands::${shorthand.ident}::to_css,
+            % endif
+            % endfor
+        ];
+
+        LONGHANDS_TO_CSS[*self as usize](declarations, dest)
     }
 
     /// Finds and returns an appendable value for the given declarations.
@@ -1591,23 +1588,20 @@ impl ShorthandId {
             input: &mut Parser<'i, 't>,
         ) -> Result<(), ParseError<'i>>;
 
-        fn unreachable<'i, 't>(
+        fn parse_all<'i, 't>(
             _: &mut SourcePropertyDeclaration,
             _: &ParserContext,
-            _: &mut Parser<'i, 't>
+            input: &mut Parser<'i, 't>
         ) -> Result<(), ParseError<'i>> {
-            unreachable!()
+            // 'all' accepts no value other than CSS-wide keywords
+            Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
         }
 
-        // 'all' accepts no value other than CSS-wide keywords
-        if *self == ShorthandId::All {
-            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-        }
 
         static PARSE_INTO: [ParseIntoFn; ${len(data.shorthands)}] = [
             % for shorthand in data.shorthands:
             % if shorthand.ident == "all":
-            unreachable,
+            parse_all,
             % else:
             shorthands::${shorthand.ident}::parse_into,
             % endif