Change ToCss to take a CssWriter<W>

This more concrete wrapper type can write a prefix the very first time something
is written to it. This allows removing plenty of useless monomorphisations caused
by the former W/SequenceWriter<W> pair of types.

components/style/stylesheets/document_rule.rs

@@ -15,7 +15,7 @@ use servo_arc::Arc;
 use shared_lock::{DeepCloneParams, DeepCloneWithLock, Locked, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
-use style_traits::{ToCss, ParseError, StyleParseErrorKind};
+use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
 use stylesheets::CssRules;
 use values::specified::url::SpecifiedUrl;
 
@@ -43,7 +43,7 @@ impl DocumentRule {
 impl ToCssWithGuard for DocumentRule {
     fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
         dest.write_str("@-moz-document ")?;
-        self.condition.to_css(dest)?;
+        self.condition.to_css(&mut CssWriter::new(dest))?;
         dest.write_str(" {")?;
         for rule in self.rules.read_with(guard).0.iter() {
             dest.write_str(" ")?;
@@ -167,8 +167,10 @@ impl UrlMatchingFunction {
 }
 
 impl ToCss for UrlMatchingFunction {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
-        where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         match *self {
             UrlMatchingFunction::Url(ref url) => {
                 url.to_css(dest)
@@ -219,8 +221,10 @@ impl DocumentCondition {
 }
 
 impl ToCss for DocumentCondition {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
-        where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         let mut iter = self.0.iter();
         let first = iter.next()
             .expect("Empty DocumentCondition, should contain at least one URL matching function");

components/style/stylesheets/font_feature_values_rule.rs

@@ -18,7 +18,7 @@ use parser::{ParserContext, ParserErrorContext, Parse};
 use shared_lock::{SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
-use style_traits::{ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
 use stylesheets::CssRuleType;
 use values::computed::font::FamilyName;
 
@@ -37,7 +37,10 @@ pub struct FFVDeclaration<T> {
 }
 
 impl<T: ToCss> ToCss for FFVDeclaration<T> {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         serialize_identifier(&self.name.to_string(), dest)?;
         dest.write_str(": ")?;
         self.value.to_css(dest)?;
@@ -101,7 +104,10 @@ impl Parse for PairValues {
 }
 
 impl ToCss for PairValues {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         self.0.to_css(dest)?;
         if let Some(second) = self.1 {
             dest.write_char(' ')?;
@@ -153,7 +159,10 @@ impl Parse for VectorValues {
 }
 
 impl ToCss for VectorValues {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         let mut iter = self.0.iter();
         let first = iter.next();
         if let Some(first) = first {
@@ -280,7 +289,13 @@ macro_rules! font_feature_values_blocks {
             }
 
             /// Prints font family names.
-            pub fn font_family_to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+            pub fn font_family_to_css<W>(
+                &self,
+                dest: &mut CssWriter<W>,
+            ) -> fmt::Result
+            where
+                W: Write,
+            {
                 let mut iter = self.family_names.iter();
                 iter.next().unwrap().to_css(dest)?;
                 for val in iter {
@@ -291,7 +306,10 @@ macro_rules! font_feature_values_blocks {
             }
 
             /// Prints inside of `@font-feature-values` block.
-            pub fn value_to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+            pub fn value_to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
                 $(
                     if self.$ident.len() > 0 {
                         dest.write_str(concat!("@", $name, " {\n"))?;
@@ -344,9 +362,9 @@ macro_rules! font_feature_values_blocks {
         impl ToCssWithGuard for FontFeatureValuesRule {
             fn to_css(&self, _guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
                 dest.write_str("@font-feature-values ")?;
-                self.font_family_to_css(dest)?;
+                self.font_family_to_css(&mut CssWriter::new(dest))?;
                 dest.write_str(" {\n")?;
-                self.value_to_css(dest)?;
+                self.value_to_css(&mut CssWriter::new(dest))?;
                 dest.write_str("}")
             }
         }

components/style/stylesheets/import_rule.rs

@@ -11,7 +11,7 @@ use media_queries::MediaList;
 use shared_lock::{DeepCloneWithLock, DeepCloneParams, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
-use style_traits::ToCss;
+use style_traits::{CssWriter, ToCss};
 use stylesheets::{StylesheetContents, StylesheetInDocument};
 use values::specified::url::SpecifiedUrl;
 
@@ -110,12 +110,12 @@ impl DeepCloneWithLock for ImportRule {
 impl ToCssWithGuard for ImportRule {
     fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
         dest.write_str("@import ")?;
-        self.url.to_css(dest)?;
+        self.url.to_css(&mut CssWriter::new(dest))?;
 
         match self.stylesheet.media(guard) {
             Some(media) if !media.is_empty() => {
                 dest.write_str(" ")?;
-                media.to_css(dest)?;
+                media.to_css(&mut CssWriter::new(dest))?;
             }
             _ => {},
         };

components/style/stylesheets/keyframes_rule.rs

@@ -16,7 +16,7 @@ use servo_arc::Arc;
 use shared_lock::{DeepCloneParams, DeepCloneWithLock, SharedRwLock, SharedRwLockReadGuard, Locked, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
-use style_traits::{ParsingMode, ToCss, ParseError, StyleParseErrorKind};
+use style_traits::{CssWriter, ParseError, ParsingMode, StyleParseErrorKind, ToCss};
 use stylesheets::{CssRuleType, StylesheetContents};
 use stylesheets::rule_parser::VendorPrefix;
 use values::{KeyframesName, serialize_percentage};
@@ -40,7 +40,7 @@ impl ToCssWithGuard for KeyframesRule {
     // Serialization of KeyframesRule is not specced.
     fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
         dest.write_str("@keyframes ")?;
-        self.name.to_css(dest)?;
+        self.name.to_css(&mut CssWriter::new(dest))?;
         dest.write_str(" {")?;
         let iter = self.keyframes.iter();
         for lock in iter {
@@ -109,7 +109,10 @@ impl ::std::cmp::Ord for KeyframePercentage {
 impl ::std::cmp::Eq for KeyframePercentage { }
 
 impl ToCss for KeyframePercentage {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         serialize_percentage(self.0, dest)
     }
 }
@@ -146,7 +149,10 @@ impl KeyframePercentage {
 pub struct KeyframeSelector(Vec<KeyframePercentage>);
 
 impl ToCss for KeyframeSelector {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         let mut iter = self.0.iter();
         iter.next().unwrap().to_css(dest)?;
         for percentage in iter {
@@ -194,7 +200,7 @@ pub struct Keyframe {
 
 impl ToCssWithGuard for Keyframe {
     fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
-        self.selector.to_css(dest)?;
+        self.selector.to_css(&mut CssWriter::new(dest))?;
         dest.write_str(" { ")?;
         self.block.read_with(guard).to_css(dest)?;
         dest.write_str(" }")?;

components/style/stylesheets/media_rule.rs

@@ -14,7 +14,7 @@ use servo_arc::Arc;
 use shared_lock::{DeepCloneParams, DeepCloneWithLock, Locked, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
-use style_traits::ToCss;
+use style_traits::{CssWriter, ToCss};
 use stylesheets::CssRules;
 
 /// An [`@media`][media] urle.
@@ -45,7 +45,7 @@ impl ToCssWithGuard for MediaRule {
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule CSSMediaRule
     fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
         dest.write_str("@media ")?;
-        self.media_queries.read_with(guard).to_css(dest)?;
+        self.media_queries.read_with(guard).to_css(&mut CssWriter::new(dest))?;
         self.rules.read_with(guard).to_css_block(guard, dest)
     }
 }

components/style/stylesheets/supports_rule.rs

@@ -18,7 +18,7 @@ use std::ffi::{CStr, CString};
 use std::fmt::{self, Write};
 use std::str;
 use str::CssStringWriter;
-use style_traits::{ToCss, ParseError};
+use style_traits::{CssWriter, ParseError, ToCss};
 use stylesheets::{CssRuleType, CssRules};
 
 /// An [`@supports`][supports] rule.
@@ -49,7 +49,7 @@ impl SupportsRule {
 impl ToCssWithGuard for SupportsRule {
     fn to_css(&self, guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
         dest.write_str("@supports ")?;
-        self.condition.to_css(dest)?;
+        self.condition.to_css(&mut CssWriter::new(dest))?;
         self.rules.read_with(guard).to_css_block(guard, dest)
     }
 }
@@ -219,8 +219,9 @@ pub fn parse_condition_or_declaration<'i, 't>(input: &mut Parser<'i, 't>)
 }
 
 impl ToCss for SupportsCondition {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
-        where W: fmt::Write,
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
     {
         match *self {
             SupportsCondition::Not(ref cond) => {
@@ -276,7 +277,10 @@ impl ToCss for SupportsCondition {
 pub struct Declaration(pub String);
 
 impl ToCss for Declaration {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         dest.write_str(&self.0)
     }
 }

components/style/stylesheets/viewport_rule.rs

@@ -27,7 +27,7 @@ use std::fmt::{self, Write};
 use std::iter::Enumerate;
 use std::str::Chars;
 use str::CssStringWriter;
-use style_traits::{PinchZoomFactor, ToCss, ParseError, StyleParseErrorKind};
+use style_traits::{CssWriter, ParseError, PinchZoomFactor, StyleParseErrorKind, ToCss};
 use style_traits::viewport::{Orientation, UserZoom, ViewportConstraints, Zoom};
 use stylesheets::{StylesheetInDocument, Origin};
 use values::computed::{Context, ToComputedValue};
@@ -101,7 +101,10 @@ macro_rules! declare_viewport_descriptor_inner {
         }
 
         impl ToCss for ViewportDescriptor {
-            fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
                 match *self {
                     $(
                         ViewportDescriptor::$assigned_variant(ref val) => {
@@ -149,8 +152,9 @@ pub enum ViewportLength {
 }
 
 impl ToCss for ViewportLength {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
-        where W: fmt::Write,
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
     {
         match *self {
             ViewportLength::Specified(ref length) => length.to_css(dest),
@@ -255,7 +259,10 @@ impl ViewportDescriptorDeclaration {
 }
 
 impl ToCss for ViewportDescriptorDeclaration {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
         self.descriptor.to_css(dest)?;
         if self.important {
             dest.write_str(" !important")?;
@@ -524,10 +531,10 @@ impl ToCssWithGuard for ViewportRule {
     fn to_css(&self, _guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
         dest.write_str("@viewport { ")?;
         let mut iter = self.declarations.iter();
-        iter.next().unwrap().to_css(dest)?;
+        iter.next().unwrap().to_css(&mut CssWriter::new(dest))?;
         for declaration in iter {
             dest.write_str(" ")?;
-            declaration.to_css(dest)?;
+            declaration.to_css(&mut CssWriter::new(dest))?;
         }
         dest.write_str(" }")
     }