Introduce "visitor" feature flag (parcel-bundler#367)

* Introduce "visitor" feature flag

This commit adds a "visitor" feature flag to the lightningcss crate.

This feature flag controls whether or not the `Visitor` trait gets
compiled. The "visitor" flag is disabled by default.

Disabling the "visitor" feature disables the `lightningcss-derive`
dependency.

This commit on its own reduces the lightningcss crate's build time by
about 8% (as measured by comparing `cargo build --timings` with and
without the "visitor" feature enabled.

When combined with some of the other soon to land commits, this commit
will make it possible to remove `syn` from the dependency tree when you
don't need it, which should lead to substantial compile time savings.

Related: parcel-bundler#357

* Specify required features for examples

Co-authored-by: Devon Govett <devongovett@gmail.com>

Author: chinedufn

Cargo.toml

@@ -34,6 +34,7 @@ cli = ["clap", "serde_json", "browserslist", "jemallocator"]
 grid = []
 nodejs = ["dep:serde"]
 serde = ["dep:serde", "smallvec/serde", "cssparser/serde"]
+visitor = ["lightningcss-derive"]
 
 [dependencies]
 serde = { version = "1.0.123", features = ["derive"], optional = true }
@@ -53,7 +54,7 @@ browserslist-rs = { version = "0.7.0", optional = true }
 rayon = { version = "1.5.1", optional = true }
 dashmap = { version = "5.0.0", optional = true }
 serde_json = { version = "1.0.78", optional = true }
-lightningcss-derive = { version = "1.0.0-alpha.35", path = "./derive" }
+lightningcss-derive = { version = "1.0.0-alpha.35", path = "./derive", optional = true }
 
 [target.'cfg(target_os = "macos")'.dependencies]
 jemallocator = { version = "0.3.2", features = ["disable_initial_exec_tls"], optional = true }
@@ -70,6 +71,14 @@ name = "cli_integration_tests"
 path = "tests/cli_integration_tests.rs"
 required-features = ["cli"]
 
+[[example]]
+name = "custom_at_rule"
+required-features = ["visitor"]
+
+[[example]]
+name = "serialize"
+required-features = ["serde"]
+
 [profile.release]
 lto = true
 codegen-units = 1

examples/custom_at_rule.rs

@@ -254,6 +254,7 @@ impl<'a, 'i> Visitor<'i, AtRule> for ApplyVisitor<'a, 'i> {
   }
 }
 
+#[cfg(feature = "visitor")]
 impl<'i, V: Visitor<'i, AtRule>> Visit<'i, AtRule, V> for AtRule {
   const CHILD_TYPES: VisitTypes = VisitTypes::empty();
 

src/declaration.rs

@@ -34,6 +34,7 @@ use crate::properties::{Property, PropertyId};
 use crate::targets::Browsers;
 use crate::traits::{PropertyHandler, ToCss};
 use crate::values::string::CowArcStr;
+#[cfg(feature = "visitor")]
 use crate::visitor::Visit;
 use cssparser::*;
 
@@ -42,7 +43,8 @@ use cssparser::*;
 /// Properties are separated into a list of `!important` declararations,
 /// and a list of normal declarations. This reduces memory usage compared
 /// with storing a boolean along with each property.
-#[derive(Debug, PartialEq, Clone, Visit)]
+#[derive(Debug, PartialEq, Clone)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct DeclarationBlock<'i> {
   /// A list of `!important` declarations in the block.

src/dependencies.rs

@@ -13,6 +13,7 @@ use crate::printer::PrinterOptions;
 use crate::rules::import::ImportRule;
 use crate::traits::ToCss;
 use crate::values::url::Url;
+#[cfg(feature = "visitor")]
 use crate::visitor::Visit;
 use cssparser::SourceLocation;
 #[cfg(any(feature = "serde", feature = "nodejs"))]
@@ -127,7 +128,8 @@ pub struct SourceRange {
 }
 
 /// A line and column position within a source file.
-#[derive(Debug, Clone, Copy, PartialEq, Visit)]
+#[derive(Debug, Clone, Copy, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(any(feature = "serde", feature = "nodejs"), derive(serde::Serialize))]
 #[cfg_attr(any(feature = "serde"), derive(serde::Deserialize))]
 pub struct Location {

src/lib.rs

@@ -38,6 +38,7 @@ pub mod targets;
 pub mod traits;
 pub mod values;
 pub mod vendor_prefix;
+#[cfg(feature = "visitor")]
 pub mod visitor;
 
 #[cfg(test)]

src/macros.rs

@@ -9,7 +9,8 @@ macro_rules! enum_property {
     }
   ) => {
     $(#[$outer])*
-    #[derive(Debug, Clone, Copy, PartialEq, Visit)]
+    #[derive(Debug, Clone, Copy, PartialEq)]
+    #[cfg_attr(feature = "visitor", derive(Visit))]
     #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize), serde(rename_all = "lowercase"))]
     $vis enum $name {
       $(
@@ -66,7 +67,7 @@ macro_rules! enum_property {
     }
   ) => {
     $(#[$outer])*
-    #[derive(Debug, Clone, Copy, PartialEq, Visit)]
+    #[derive(Debug, Clone, Copy, PartialEq)] #[cfg_attr(feature = "visitor", derive(Visit))]
     #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
     $vis enum $name {
       $(
@@ -339,7 +340,8 @@ macro_rules! define_shorthand {
     }
   ) => {
     $(#[$outer])*
-    #[derive(Debug, Clone, PartialEq, Visit)]
+    #[derive(Debug, Clone, PartialEq)]
+    #[cfg_attr(feature = "visitor", derive(Visit))]
     #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
     pub struct $name$(<$l>)? {
       $(
@@ -553,7 +555,8 @@ macro_rules! define_list_shorthand {
     }
   ) => {
     $(#[$outer])*
-    #[derive(Debug, Clone, PartialEq, Visit)]
+    #[derive(Debug, Clone, PartialEq)]
+    #[cfg_attr(feature = "visitor", derive(Visit))]
     #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
     pub struct $name$(<$l>)? {
       $(

src/media_query.rs

@@ -12,12 +12,14 @@ use crate::values::ident::Ident;
 use crate::values::number::CSSNumber;
 use crate::values::string::CowArcStr;
 use crate::values::{length::Length, ratio::Ratio, resolution::Resolution};
+#[cfg(feature = "visitor")]
 use crate::visitor::Visit;
 use cssparser::*;
 use std::collections::{HashMap, HashSet};
 
 /// A [media query list](https://drafts.csswg.org/mediaqueries/#mq-list).
-#[derive(Clone, Debug, PartialEq, Visit)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct MediaList<'i> {
   /// The list of media queries.
@@ -144,7 +146,8 @@ enum_property! {
 }
 
 /// A [media type](https://drafts.csswg.org/mediaqueries/#media-types) within a media query.
-#[derive(Clone, Debug, PartialEq, Visit)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -176,8 +179,9 @@ impl<'i> Parse<'i> for MediaType<'i> {
 }
 
 /// A [media query](https://drafts.csswg.org/mediaqueries/#media).
-#[derive(Clone, Debug, PartialEq, Visit)]
-#[visit(visit_media_query, MEDIA_QUERIES)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
+#[cfg_attr(feature = "visitor", visit(visit_media_query, MEDIA_QUERIES))]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct MediaQuery<'i> {
   /// The qualifier for this query.
@@ -360,7 +364,8 @@ enum_property! {
 }
 
 /// Represents a media condition.
-#[derive(Clone, Debug, PartialEq, Visit)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -371,10 +376,10 @@ pub enum MediaCondition<'i> {
   #[cfg_attr(feature = "serde", serde(borrow))]
   Feature(MediaFeature<'i>),
   /// A negation of a condition.
-  #[skip_type]
+  #[cfg_attr(feature = "visitor", skip_type)]
   Not(Box<MediaCondition<'i>>),
   /// A set of joint operations.
-  #[skip_type]
+  #[cfg_attr(feature = "visitor", skip_type)]
   Operation(Vec<MediaCondition<'i>>, Operator),
 }
 
@@ -495,7 +500,8 @@ impl<'i> ToCss for MediaCondition<'i> {
 }
 
 /// A [comparator](https://drafts.csswg.org/mediaqueries/#typedef-mf-comparison) within a media query.
-#[derive(Clone, Copy, Debug, Eq, PartialEq, Visit)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -551,7 +557,8 @@ impl MediaFeatureComparison {
 }
 
 /// A [media feature](https://drafts.csswg.org/mediaqueries/#typedef-media-feature)
-#[derive(Clone, Debug, PartialEq, Visit)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -753,7 +760,8 @@ where
 /// [media feature value](https://drafts.csswg.org/mediaqueries/#typedef-mf-value) within a media query.
 ///
 /// See [MediaFeature](MediaFeature).
-#[derive(Clone, Debug, PartialEq, Visit)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),

src/parser.rs

@@ -30,6 +30,7 @@ use crate::traits::Parse;
 use crate::values::ident::{CustomIdent, DashedIdent};
 use crate::values::string::CowArcStr;
 use crate::vendor_prefix::VendorPrefix;
+#[cfg(feature = "visitor")]
 use crate::visitor::{Visit, VisitTypes, Visitor};
 use cssparser::*;
 use parcel_selectors::parser::NestingRequirement;
@@ -110,6 +111,7 @@ impl crate::traits::ToCss for DefaultAtRule {
   }
 }
 
+#[cfg(feature = "visitor")]
 impl<'i, V: Visitor<'i, DefaultAtRule>> Visit<'i, DefaultAtRule, V> for DefaultAtRule {
   const CHILD_TYPES: VisitTypes = VisitTypes::empty();
   fn visit_children(&mut self, _: &mut V) {}

src/properties/align.rs

@@ -13,12 +13,14 @@ use crate::targets::Browsers;
 use crate::traits::{FromStandard, Parse, PropertyHandler, Shorthand, ToCss};
 use crate::values::length::LengthPercentage;
 use crate::vendor_prefix::VendorPrefix;
+#[cfg(feature = "visitor")]
 use crate::visitor::Visit;
 use cssparser::*;
 
 /// A [`<baseline-position>`](https://www.w3.org/TR/css-align-3/#typedef-baseline-position) value,
 /// as used in the alignment properties.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -107,7 +109,8 @@ enum_property! {
 }
 
 /// A value for the [align-content](https://www.w3.org/TR/css-align-3/#propdef-align-content) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -166,7 +169,8 @@ impl ToCss for AlignContent {
 }
 
 /// A value for the [justify-content](https://www.w3.org/TR/css-align-3/#propdef-justify-content) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -327,7 +331,8 @@ enum_property! {
 }
 
 /// A value for the [align-self](https://www.w3.org/TR/css-align-3/#align-self-property) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -393,7 +398,8 @@ impl ToCss for AlignSelf {
 }
 
 /// A value for the [justify-self](https://www.w3.org/TR/css-align-3/#justify-self-property) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -549,7 +555,8 @@ impl ToCss for PlaceSelf {
 }
 
 /// A value for the [align-items](https://www.w3.org/TR/css-align-3/#align-items-property) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -608,7 +615,8 @@ impl ToCss for AlignItems {
 }
 
 /// A legacy justification keyword, as used in the `justify-items` property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -674,7 +682,8 @@ impl ToCss for LegacyJustify {
 }
 
 /// A value for the [justify-items](https://www.w3.org/TR/css-align-3/#justify-items-property) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -829,7 +838,8 @@ impl ToCss for PlaceItems {
 
 /// A [gap](https://www.w3.org/TR/css-align-3/#column-row-gap) value, as used in the
 /// `column-gap` and `row-gap` properties.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),

src/properties/animation.rs

@@ -12,13 +12,15 @@ use crate::traits::{Parse, PropertyHandler, Shorthand, ToCss, Zero};
 use crate::values::number::CSSNumber;
 use crate::values::string::CowArcStr;
 use crate::values::{easing::EasingFunction, ident::CustomIdent, time::Time};
+#[cfg(feature = "visitor")]
 use crate::visitor::Visit;
 use cssparser::*;
 use itertools::izip;
 use smallvec::SmallVec;
 
 /// A value for the [animation-name](https://drafts.csswg.org/css-animations/#animation-name) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),
@@ -87,7 +89,8 @@ impl<'i> ToCss for AnimationName<'i> {
 pub type AnimationNameList<'i> = SmallVec<[AnimationName<'i>; 1]>;
 
 /// A value for the [animation-iteration-count](https://drafts.csswg.org/css-animations/#animation-iteration-count) property.
-#[derive(Debug, Clone, PartialEq, Visit)]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
 #[cfg_attr(
   feature = "serde",
   derive(serde::Serialize, serde::Deserialize),