Use smallvec to avoid heap allocations

Author: devongovett

Cargo.lock

@@ -17,6 +17,7 @@ cssparser-macros = "*"
 selectors = "*"
 indoc = "*"
 itertools = "*"
+smallvec = "1.7.0"
 
 [build-dependencies]
 napi-build = { version = "1" }

Cargo.toml

@@ -6,6 +6,7 @@ extern crate serde_bytes;
 extern crate cssparser;
 extern crate selectors;
 extern crate itertools;
+extern crate smallvec;
 
 mod parser;
 mod rules;

src/lib.rs

@@ -1,11 +1,12 @@
 use cssparser::*;
 use crate::traits::{Parse, ToCss, PropertyHandler};
-use crate::values::{ident::CustomIdent, time::Time, easing::EasingFunction};
+use crate::values::{time::Time, easing::EasingFunction};
 use super::Property;
 use crate::printer::Printer;
 use std::fmt::Write;
 use itertools::izip;
 use crate::macros::*;
+use smallvec::SmallVec;
 
 /// https://drafts.csswg.org/css-animations/#animation-name
 #[derive(Debug, Clone, PartialEq)]
@@ -197,14 +198,14 @@ impl ToCss for Animation {
 
 #[derive(Default)]
 pub struct AnimationHandler {
-  names: Option<Vec<AnimationName>>,
-  durations: Option<Vec<Time>>,
-  timing_functions: Option<Vec<EasingFunction>>,
-  iteration_counts: Option<Vec<AnimationIterationCount>>,
-  directions: Option<Vec<AnimationDirection>>,
-  play_states: Option<Vec<AnimationPlayState>>,
-  delays: Option<Vec<Time>>,
-  fill_modes: Option<Vec<AnimationFillMode>>
+  names: Option<SmallVec<[AnimationName; 1]>>,
+  durations: Option<SmallVec<[Time; 1]>>,
+  timing_functions: Option<SmallVec<[EasingFunction; 1]>>,
+  iteration_counts: Option<SmallVec<[AnimationIterationCount; 1]>>,
+  directions: Option<SmallVec<[AnimationDirection; 1]>>,
+  play_states: Option<SmallVec<[AnimationPlayState; 1]>>,
+  delays: Option<SmallVec<[Time; 1]>>,
+  fill_modes: Option<SmallVec<[AnimationFillMode; 1]>>
 }
 
 impl PropertyHandler for AnimationHandler {

src/properties/animation.rs

@@ -6,6 +6,7 @@ use crate::values::{color::CssColor, image::Image};
 use crate::properties::Property;
 use itertools::izip;
 use crate::printer::Printer;
+use smallvec::SmallVec;
 
 /// https://www.w3.org/TR/css-backgrounds-3/#background-position
 #[derive(Debug, Clone, PartialEq)]
@@ -463,14 +464,14 @@ impl ToCss for Background {
 #[derive(Default)]
 pub struct BackgroundHandler {
   color: Option<CssColor>,
-  images: Option<Vec<Image>>,
-  x_positions: Option<Vec<HorizontalPosition>>,
-  y_positions: Option<Vec<VerticalPosition>>,
-  repeats: Option<Vec<BackgroundRepeat>>,
-  sizes: Option<Vec<BackgroundSize>>,
-  attachments: Option<Vec<BackgroundAttachment>>,
-  origins: Option<Vec<BackgroundBox>>,
-  clips: Option<Vec<BackgroundBox>>
+  images: Option<SmallVec<[Image; 1]>>,
+  x_positions: Option<SmallVec<[HorizontalPosition; 1]>>,
+  y_positions: Option<SmallVec<[VerticalPosition; 1]>>,
+  repeats: Option<SmallVec<[BackgroundRepeat; 1]>>,
+  sizes: Option<SmallVec<[BackgroundSize; 1]>>,
+  attachments: Option<SmallVec<[BackgroundAttachment; 1]>>,
+  origins: Option<SmallVec<[BackgroundBox; 1]>>,
+  clips: Option<SmallVec<[BackgroundBox; 1]>>
 }
 
 impl PropertyHandler for BackgroundHandler {

src/properties/background.rs

@@ -5,6 +5,7 @@ use crate::traits::{Parse, ToCss, PropertyHandler};
 use super::Property;
 use crate::printer::Printer;
 use std::fmt::Write;
+use smallvec::SmallVec;
 
 /// https://www.w3.org/TR/2021/WD-css-fonts-4-20210729/#font-weight-prop
 #[derive(Debug, Clone, PartialEq)]

src/properties/font.rs

@@ -29,23 +29,24 @@ use crate::values::{image::*, length::*, rect::*, color::*, time::Time, ident::C
 use crate::traits::{Parse, ToCss};
 use crate::printer::Printer;
 use std::fmt::Write;
+use smallvec::{SmallVec, smallvec};
 
 #[derive(Debug, Clone, PartialEq)]
 pub enum Property {
   BackgroundColor(CssColor),
-  BackgroundImage(Vec<Image>),
-  BackgroundPositionX(Vec<HorizontalPosition>),
-  BackgroundPositionY(Vec<VerticalPosition>),
-  BackgroundPosition(Vec<BackgroundPosition>),
-  BackgroundSize(Vec<BackgroundSize>),
-  BackgroundRepeat(Vec<BackgroundRepeat>),
-  BackgroundAttachment(Vec<BackgroundAttachment>),
-  BackgroundClip(Vec<BackgroundBox>),
-  BackgroundOrigin(Vec<BackgroundBox>),
+  BackgroundImage(SmallVec<[Image; 1]>),
+  BackgroundPositionX(SmallVec<[HorizontalPosition; 1]>),
+  BackgroundPositionY(SmallVec<[VerticalPosition; 1]>),
+  BackgroundPosition(SmallVec<[BackgroundPosition; 1]>),
+  BackgroundSize(SmallVec<[BackgroundSize; 1]>),
+  BackgroundRepeat(SmallVec<[BackgroundRepeat; 1]>),
+  BackgroundAttachment(SmallVec<[BackgroundAttachment; 1]>),
+  BackgroundClip(SmallVec<[BackgroundBox; 1]>),
+  BackgroundOrigin(SmallVec<[BackgroundBox; 1]>),
   // BackgroundBlendMode
-  Background(Vec<Background>),
+  Background(SmallVec<[Background; 1]>),
 
-  BoxShadow(Vec<BoxShadow>),
+  BoxShadow(SmallVec<[BoxShadow; 1]>),
   Opacity(AlphaValue),
 
   Color(CssColor),
@@ -235,36 +236,55 @@ pub enum Property {
   LineHeight(LineHeight),
   Font(Font),
 
-  TransitionProperty(Vec<CustomIdent>),
-  TransitionDuration(Vec<Time>),
-  TransitionDelay(Vec<Time>),
-  TransitionTimingFunction(Vec<EasingFunction>),
-  Transition(Vec<Transition>),
+  TransitionProperty(SmallVec<[CustomIdent; 1]>),
+  TransitionDuration(SmallVec<[Time; 1]>),
+  TransitionDelay(SmallVec<[Time; 1]>),
+  TransitionTimingFunction(SmallVec<[EasingFunction; 1]>),
+  Transition(SmallVec<[Transition; 1]>),
 
-  AnimationName(Vec<AnimationName>),
-  AnimationDuration(Vec<Time>),
-  AnimationTimingFunction(Vec<EasingFunction>),
-  AnimationIterationCount(Vec<AnimationIterationCount>),
-  AnimationDirection(Vec<AnimationDirection>),
-  AnimationPlayState(Vec<AnimationPlayState>),
-  AnimationDelay(Vec<Time>),
-  AnimationFillMode(Vec<AnimationFillMode>),
-  Animation(Vec<Animation>)
+  AnimationName(SmallVec<[AnimationName; 1]>),
+  AnimationDuration(SmallVec<[Time; 1]>),
+  AnimationTimingFunction(SmallVec<[EasingFunction; 1]>),
+  AnimationIterationCount(SmallVec<[AnimationIterationCount; 1]>),
+  AnimationDirection(SmallVec<[AnimationDirection; 1]>),
+  AnimationPlayState(SmallVec<[AnimationPlayState; 1]>),
+  AnimationDelay(SmallVec<[Time; 1]>),
+  AnimationFillMode(SmallVec<[AnimationFillMode; 1]>),
+  Animation(SmallVec<[Animation; 1]>)
 }
 
 impl Property {
   pub fn parse<'i, 't>(name: CowRcStr<'i>, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i, ()>> {
     macro_rules! property {
+      // font-family is special because it uses Vec rather than SmallVec
+      // It's likely that there will be more than one font family vs other
+      // properties where only one is the common case.
+      (FontFamily, $type: ident) => {
+        if let Ok(c) = input.parse_comma_separated(|input| $type::parse(input)) {
+          return Ok(Property::FontFamily(c))
+        }
+      };
       ($property: ident, $type: ident) => {
         if let Ok(c) = $type::parse(input) {
           return Ok(Property::$property(c))
         }
       };
-      ($property: ident, $type: ident, $multi: expr) => {
-        if let Ok(c) = input.parse_comma_separated(|input| $type::parse(input)) {
-          return Ok(Property::$property(c))
+      ($property: ident, $type: ident, $multi: expr) => {{
+        // Copied from cssparser `parse_comma_separated` but using SmallVec instead of Vec.
+        let mut values = smallvec![];
+        loop {
+          input.skip_whitespace(); // Unnecessary for correctness, but may help try() in parse_one rewind less.
+          match input.parse_until_before(Delimiter::Comma, &mut $type::parse) {
+            Ok(v) => values.push(v),
+            Err(_) => break
+          }
+          match input.next() {
+            Err(_) => return Ok(Property::$property(values)),
+            Ok(&Token::Comma) => continue,
+            Ok(_) => unreachable!(),
+          }
         }
-      }
+      }};
     }
 
     let state = input.state();
@@ -436,7 +456,7 @@ impl Property {
       "font-weight" => property!(FontWeight, FontWeight),
       "font-size" => property!(FontSize, FontSize),
       "font-stretch" => property!(FontStretch, FontStretch),
-      "font-family" => property!(FontFamily, FontFamily, true),
+      "font-family" => property!(FontFamily, FontFamily),
       "font-style" => property!(FontStyle, FontStyle),
       "font-variant-caps" => property!(FontVariantCaps, FontVariantCaps),
       "line-height" => property!(LineHeight, LineHeight),

src/properties/mod.rs

@@ -5,6 +5,7 @@ use super::Property;
 use crate::printer::Printer;
 use std::fmt::Write;
 use itertools::izip;
+use smallvec::SmallVec;
 
 /// https://www.w3.org/TR/2018/WD-css-transitions-1-20181011/#transition-shorthand-property
 #[derive(Debug, Clone, PartialEq)]
@@ -87,10 +88,10 @@ impl ToCss for Transition {
 
 #[derive(Default)]
 pub struct TransitionHandler {
-  properties: Option<Vec<CustomIdent>>,
-  durations: Option<Vec<Time>>,
-  delays: Option<Vec<Time>>,
-  timing_functions: Option<Vec<EasingFunction>> 
+  properties: Option<SmallVec<[CustomIdent; 1]>>,
+  durations: Option<SmallVec<[Time; 1]>>,
+  delays: Option<SmallVec<[Time; 1]>>,
+  timing_functions: Option<SmallVec<[EasingFunction; 1]>> 
 }
 
 impl PropertyHandler for TransitionHandler {