Converted serialization methods to implement the to_css trait, writing to string buffers to save string allocations for every result

components/script/dom/cssstyledeclaration.rs

@@ -10,7 +10,7 @@ use dom::bindings::js::{JS, Root};
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::str::DOMString;
 use dom::element::{Element, StylePriority};
-use dom::node::{Node, NodeDamage, window_from_node};
+use dom::node::{Node, window_from_node};
 use dom::window::Window;
 use std::ascii::AsciiExt;
 use string_cache::Atom;
@@ -147,7 +147,8 @@ impl CSSStyleDeclarationMethods for CSSStyleDeclaration {
 
             // Step 2.3
             let list = list.iter().map(|x| &*x).collect::<Vec<_>>();
-            return DOMString::from(shorthand.serialize_shorthand(&list));
+            let serialized_value = shorthand.serialize_shorthand_to_string(&list);
+            return DOMString::from(serialized_value);
         }
 
         // Step 3 & 4

components/script/dom/element.rs

@@ -5,7 +5,7 @@
 //! Element nodes.
 
 use app_units::Au;
-use cssparser::Color;
+use cssparser::{Color, ToCss};
 use devtools_traits::AttrInfo;
 use dom::activation::Activatable;
 use dom::attr::AttrValue;
@@ -699,12 +699,10 @@ impl Element {
     }
 
     fn sync_property_with_attrs_style(&self) {
-        let style_str = if let &Some(ref declarations) = &*self.style_attribute().borrow() {
-            declarations.serialize()
+        let mut style_str = String::new();
+        if let &Some(ref declarations) = &*self.style_attribute().borrow() {
+            declarations.to_css(&mut style_str).unwrap();
         }
-        else {
-            String::new()
-        };
 
         let new_style = AttrValue::String(style_str);
 

components/style/properties/properties.mako.rs

@@ -14,6 +14,7 @@ use std::ascii::AsciiExt;
 use std::boxed::Box as StdBox;
 use std::collections::HashSet;
 use std::fmt;
+use std::fmt::Write;
 use std::intrinsics;
 use std::mem;
 use std::sync::Arc;
@@ -266,11 +267,12 @@ pub struct PropertyDeclarationBlock {
     pub normal: Arc<Vec<PropertyDeclaration>>,
 }
 
-impl PropertyDeclarationBlock {
+impl ToCss for PropertyDeclarationBlock {
     // https://drafts.csswg.org/cssom/#serialize-a-css-declaration-block
-    pub fn serialize(&self) -> String {
-        // Step 1
-        let mut result_list = String::new();
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        let mut is_first_serialization = true; // trailing serializations should have a prepended space
+
+        // Step 1 -> dest = result list
 
         // Step 2
         let mut already_serialized = Vec::new();
@@ -326,16 +328,15 @@ impl PropertyDeclarationBlock {
 
                     // TODO: serialize shorthand does not take is_important into account currently
                     // Substep 5
-                    let value = shorthand.serialize_shorthand(&current_longhands[..]);
+                    let was_serialized =
+                        try!(shorthand.serialize_shorthand_to_buffer(dest, &current_longhands[..], &mut is_first_serialization));
+                    // If serialization occured, Substep 7 & 8 will have been completed
 
                     // Substep 6
-                    if value.is_empty() {
+                    if !was_serialized {
                         continue;
                     }
 
-                    // Substep 7 & 8
-                    result_list.push_str(&format!("{}: {}; ", &shorthand.name(), value));
-
                     for current_longhand in current_longhands {
                         // Substep 9
                         already_serialized.push(current_longhand.name());
@@ -353,24 +354,63 @@ impl PropertyDeclarationBlock {
                 continue;
             }
 
-            // Step 3.3.5
-            let mut value = declaration.value();
-            if self.important.contains(declaration) {
-                value.push_str(" !important");
-            }
-            // Steps 3.3.6 & 3.3.7
-            result_list.push_str(&format!("{}: {}; ", &property, value));
+            // Steps 3.3.5, 3.3.6 & 3.3.7
+            let append_important = self.important.contains(declaration);
+            try!(append_serialization(dest,
+                                 &property.to_string(),
+                                 AppendableValue::Declaration(declaration),
+                                 append_important,
+                                 &mut is_first_serialization));
 
             // Step 3.3.8
             already_serialized.push(property);
         }
 
-        result_list.pop(); // remove trailling whitespace
         // Step 4
-        result_list
+        Ok(())
     }
 }
 
+enum AppendableValue<'a> {
+    Declaration(&'a PropertyDeclaration),
+    Css(&'a str)
+}
+
+fn append_serialization<W>(dest: &mut W,
+                           property_name: &str,
+                           appendable_value: AppendableValue,
+                           is_important: bool,
+                           is_first_serialization: &mut bool) -> fmt::Result where W: fmt::Write
+
+    // after first serialization(key: value;) add whitespace between the pairs
+    if !*is_first_serialization {
+        try!(write!(dest, " "));
+    }
+    else {
+        *is_first_serialization = false;
+    }
+
+    try!(write!(dest, "{}:", property_name));
+
+    match appendable_value {
+        AppendableValue::Declaration(decl) => {
+            if !decl.value_is_unparsed() {
+                // for normal parsed values, add a space between key: and value
+                try!(write!(dest, " "));
+            }
+
+            try!(decl.to_css(dest));
+         },
+        AppendableValue::Css(css) =>  try!(write!(dest, "{}", css))
+    };
+
+    if is_important {
+        try!(write!(dest, " !important"));
+    }
+
+    write!(dest, ";")
+}
+
 pub fn parse_style_attribute(input: &str, base_url: &Url, error_reporter: StdBox<ParseErrorReporter + Send>,
                              extra_data: ParserContextExtraData)
                              -> PropertyDeclarationBlock {
@@ -509,8 +549,6 @@ pub enum Shorthand {
     % endfor
 }
 
-use util::str::str_join;
-
 impl Shorthand {
     pub fn from_name(name: &str) -> Option<Shorthand> {
         match_ignore_ascii_case! { name,
@@ -544,25 +582,48 @@ impl Shorthand {
         }
     }
 
-    pub fn serialize_shorthand(self, declarations: &[&PropertyDeclaration]) -> String {
+    /// Serializes possible shorthand value to String.
+    pub fn serialize_shorthand_to_string(self, declarations: &[&PropertyDeclaration]) -> String {
+        let mut result = String::new();
+        self.serialize_shorthand_to_buffer(&mut result, declarations, &mut true).unwrap();
+        result
+    }
+
+    /// Serializes possible shorthand value to input buffer given a list of longhand declarations.
+    /// On success, returns true if shorthand value is written and false if no shorthand value is present.
+    pub fn serialize_shorthand_to_buffer<W>(self,
+                                            dest: &mut W,
+                                            declarations: &[&PropertyDeclaration],
+                                            is_first_serialization: &mut bool)
+         -> Result<bool, fmt::Error> where W: Write {
+
+        let property_name = self.name();
+
         // https://drafts.csswg.org/css-variables/#variables-in-shorthands
         if let Some(css) = declarations[0].with_variables_from_shorthand(self) {
             if declarations[1..]
                    .iter()
                    .all(|d| d.with_variables_from_shorthand(self) == Some(css)) {
-                css.to_owned()
+
+                       append_serialization(
+                           dest, property_name, AppendableValue::Css(css), false, is_first_serialization
+                       ).and_then(|_| Ok(true))
             } else {
-                String::new()
+                Ok(false)
             }
         } else {
             if declarations.iter().any(|d| d.with_variables()) {
-                String::new()
+                Ok(false)
             } else {
-                let str_iter = declarations.iter().map(|d| d.value());
+                for declaration in declarations.iter() {
+                    try!(append_serialization(
+                        dest, property_name, AppendableValue::Declaration(declaration), false, is_first_serialization
+                    ));
+                }
                 // FIXME: this needs property-specific code, which probably should be in style/
                 // "as appropriate according to the grammar of shorthand "
                 // https://drafts.csswg.org/cssom/#serialize-a-css-value
-                str_join(str_iter, " ")
+                Ok(true)
             }
         }
     }
@@ -647,6 +708,22 @@ impl fmt::Display for PropertyDeclarationName {
         }
     }
 }
+impl ToCss for PropertyDeclaration {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        match *self {
+            % for property in LONGHANDS:
+                % if property.derived_from is None:
+                    PropertyDeclaration::${property.camel_case}(ref value) =>
+                        value.to_css(dest),
+                % endif
+            % endfor
+            PropertyDeclaration::Custom(_, ref value) => value.to_css(dest),
+            % if any(property.derived_from for property in data.longhands):
+                _ => Err(fmt::Error),
+            % endif
+        }
+    }
+}
 
 impl PropertyDeclaration {
     pub fn name(&self) -> PropertyDeclarationName {
@@ -666,17 +743,12 @@ impl PropertyDeclaration {
     }
 
     pub fn value(&self) -> String {
-        match *self {
-            % for property in data.longhands:
-                PropertyDeclaration::${property.camel_case}
-                % if not property.derived_from:
-                    (ref value) => value.to_css_string(),
-                % else:
-                    (_) => panic!("unsupported property declaration: ${property.name}"),
-                % endif
-            % endfor
-            PropertyDeclaration::Custom(_, ref value) => value.to_css_string(),
+        let mut value = String::new();
+        if let Err(_) = self.to_css(&mut value) {
+            panic!("unsupported property declaration: {}", self.name());
         }
+
+        value
     }
 
     /// If this is a pending-substitution value from the given shorthand, return that value
@@ -714,6 +786,20 @@ impl PropertyDeclaration {
         }
     }
 
+    /// Return whether the value is stored as it was in the CSS source, preserving whitespace
+    /// (as opposed to being parsed into a more abstract data structure).
+    /// This is the case of custom properties and values that contain unsubstituted variables.
+    pub fn value_is_unparsed(&self) -> bool {
+      match *self {
+          % for property in LONGHANDS:
+              PropertyDeclaration::${property.camel_case}(ref value) => {
+                  matches!(*value, DeclaredValue::WithVariables { .. })
+              },
+          % endfor
+          PropertyDeclaration::Custom(..) => true
+      }
+    }
+
     pub fn matches(&self, name: &str) -> bool {
         match *self {
             % for property in data.longhands:

tests/unit/style/properties.rs

@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use cssparser::ToCss;
 use rustc_serialize::json::Json;
 use std::env;
 use std::fs::{File, remove_file};
@@ -83,10 +84,10 @@ fn property_declaration_block_should_serialize_correctly() {
         important: Arc::new(important)
     };
 
-    let css_string = block.serialize();
+    let css_string = block.to_css_string();
 
     assert_eq!(
         css_string,
-        "width: 70px; min-height: 20px; display: inline-block; height: 20px ! important;"
+        "width: 70px; min-height: 20px; display: inline-block; height: 20px !important;"
     );
 }