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Make Declarations#to_s ~24x faster: its clean-up regexp matched at every character #193

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grosser merged 3 commits into from
Oct 26, 2026
+12 −5
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Make Declarations#to_s ~24x faster: its clean-up regexp matched at every character #193

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1c16567
Speed up Declarations#to_s: stop its clean-up regexp from matching at…
czj Oct 23, 2026
68bfef2
Allocate less when looking up and shortening declarations
czj Oct 23, 2026
7ec0f07
Convert the property to a string before matching it, so symbols skip …
czj Oct 24, 2026
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
## Ruby CSS Parser CHANGELOG

### Unreleased
* Speed up `RuleSet::Declarations#to_s` ~20x: its clean-up regexp matched the empty string at every character (`[\n\r\f\t]*`), making `gsub!` replace at every position; the unreachable `\s+$` branch is dropped, output unchanged
* Allocate less in `RuleSet`: skip the downcased copy of already normalized property names, and build dimension shorthands without enumerators

### Version 3.3.0
* Fix Arbitrary local-file read via attacker-controlled `@import`
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15 changes: 10 additions & 5 deletions lib/css_parser/rule_set.rb
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Expand Up @@ -18,6 +18,8 @@ class RuleSet

NUMBER_OF_DIMENSIONS = 4

NORMALIZED_PROPERTY_RX = /\A[-a-z0-9_]+\z/.freeze

DIMENSIONS = [
['margin', %w[margin-top margin-right margin-bottom margin-left]],
['padding', %w[padding-top padding-right padding-bottom padding-left]],
Expand Down Expand Up @@ -205,8 +207,7 @@ def to_s(options = {})
importance = options[:force_important] || value.important ? ' !important' : ''
memo << "#{prop}: #{value.value}#{importance}; "
end
# TODO: Clean-up regexp doesn't seem to work
str.gsub!(/^[\s^({)]+|[\n\r\f\t]*|\s+$/mx, '')
str.gsub!(/^[\s^({)]+|[\n\r\f\t]+/, '')

@grosser grosser Oct 24, 2026

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this used to remove trailing whitespaces, don't we need that ?

@grosser grosser Oct 24, 2026

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hmm "since the leftmost alternative always wins, the trailing \s+$ branch can never match"

str.gsub!(/^[\s^({)]+|[\n\r\f\t]*|\s+$/mx, '')

the problem is the middle, it matches every string, so that end never worked

@grosser grosser Oct 24, 2026

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so yeah this should work and we did not really need the /m or /x either

@czj czj Oct 24, 2026

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Exactly, the * in the middle matched the empty string everywhere, so \s+$ never got a chance; the str.strip! right after is what actually removes the trailing whitespace. And yes, the /m and /x flags are already gone in this version. Thanks a lot for the careful review, and for maintaining css_parser!

str.strip!
str
end
Expand All @@ -226,7 +227,10 @@ def ==(other)
attr_writer :declarations

def normalize_property(property)
property = property.to_s.downcase
property = property.to_s
return property if property.match?(NORMALIZED_PROPERTY_RX)

property = property.downcase
property.strip!
property
end
Expand Down Expand Up @@ -584,10 +588,11 @@ def create_dimensions_shorthand! # :nodoc:
return if declarations.size < NUMBER_OF_DIMENSIONS

DIMENSIONS.each do |property, dimensions|
values = DIMENSION_DIRECTIONS.each_with_index.with_object({}) do |(side, index), result|
values = {}
DIMENSION_DIRECTIONS.each_with_index do |side, index|
next unless (declaration = declarations[dimensions[index]])

result[side] = declaration.value
values[side] = declaration.value
end

# All four dimensions must be present
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