Prefer !important rules over non-!important rules in the same ruleset

Previously, the css rule "color: black !important; color: red;" would be
collapsed to "color: red;" as the processor did not take whether the
!important flag was set inside the same rule.

This commit makes the Declaration Value initializer take notice of the
!important flag and correctly handle it.

Author: mogest

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Unreleased
 
+* Prefer `!important` rules over non-`!important` rules in the same ruleset
 * Minor performance improvements
 
 ### Version v1.21.0

lib/css_parser/rule_set.rb

@@ -89,17 +89,20 @@ def initialize(declarations = {})
       #   puts declarations['margin']
       #   => #<CssParser::RuleSet::Declarations::Value:0x00000000030c1838 @important=true, @order=2, @value="0px auto">
       #
-      # If the property already exists its value will be over-written.
+      # If the property already exists its value will be over-written unless it was !important and the new value
+      # is not !important.
       # If the value is empty - property will be deleted
       def []=(property, value)
         property = normalize_property(property)
+        currently_important = declarations[property]&.important
 
-        if value.is_a?(Value)
+        if value.is_a?(Value) && (!currently_important || value.important)
           declarations[property] = value
         elsif value.to_s.strip.empty?
           delete property
         else
-          declarations[property] = Value.new(value)
+          value = Value.new(value)
+          declarations[property] = value if !currently_important || value.important
         end
       rescue ArgumentError => e
         raise e.exception, "#{property} #{e.message}"

test/test_merging.rb

@@ -109,6 +109,18 @@ def test_merging_important
     assert_equal 'black !important;', merged['color']
   end
 
+  def test_prioritising_important_over_non_important_in_the_same_block
+    rs1 = RuleSet.new(block: 'color: black !important; color: red;')
+    merged = CssParser.merge(rs1)
+    assert_equal 'black !important;', merged['color']
+  end
+
+  def test_prioritising_two_important_declarations_in_the_same_block
+    rs1 = RuleSet.new(block: 'color: black !important; color: red !important;')
+    merged = CssParser.merge(rs1)
+    assert_equal 'red !important;', merged['color']
+  end
+
   def test_merging_multiple_important
     rs1 = RuleSet.new(block: 'color: black !important;', specificity: 1000)
     rs2 = RuleSet.new(block: 'color: red !important;', specificity: 1)