Handle Liquid v4 'empty' and 'blank' values explicitly

Prevents a lookup error since Liquid::Expression::MethodLiteral doesn't exist in v5

.github/workflows/ci.yml

@@ -26,6 +26,9 @@ jobs:
             ruby_version: "3.1"
           - label: JRuby 9.3.4.0
             ruby_version: "jruby-9.3.4.0"
+          - label: Liquid 4
+            ruby_version: 3.1
+            liquid_version: "~> 4.0"
     steps:
       - name: Checkout Repository
         uses: actions/checkout@v3
@@ -34,6 +37,8 @@ jobs:
         with:
           ruby-version: ${{ matrix.ruby_version }}
           bundler-cache: true
+        env:
+          LIQUID_VERSION: ${{ matrix.liquid_version }}
       - name: Run Minitest based tests
         run: bash script/test
       - name: Run Cucumber based tests

Gemfile

@@ -5,6 +5,10 @@ gemspec :name => "jekyll"
 
 gem "rake", "~> 13.0"
 
+if ENV["LIQUID_VERSION"] && ENV["LIQUID_VERSION"] != ""
+  gem "liquid", ENV["LIQUID_VERSION"]
+end
+
 group :development do
   gem "launchy", "~> 2.3"
   gem "pry"

jekyll.gemspec

@@ -40,7 +40,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency("jekyll-watch",          "~> 2.0")
   s.add_runtime_dependency("kramdown",              "~> 2.3", ">= 2.3.1")
   s.add_runtime_dependency("kramdown-parser-gfm",   "~> 1.0")
-  s.add_runtime_dependency("liquid",                "~> 4.0")
+  s.add_runtime_dependency("liquid",                ">= 4.0", "< 6.0")
   s.add_runtime_dependency("mercenary",             ">= 0.3.6", "< 0.5")
   s.add_runtime_dependency("pathutil",              "~> 0.9")
 

lib/jekyll/filters.rb

@@ -398,11 +398,17 @@ module Jekyll
     # `where` filter helper
     #
     def compare_property_vs_target(property, target)
+      # Liquid v4 handles 'empty' and 'blank' keywords separately from v5.
+      # Delete when we remove Liquid v5 support.
+      if Liquid::VERSION.start_with?("4.") && target.is_a?(Liquid::Expression::MethodLiteral)
+        target = target.to_s
+        return true if property == target || Array(property).join == target
+      end
+
       case target
       when NilClass
         return true if property.nil?
-      when Liquid::Expression::MethodLiteral # `empty` or `blank`
-        target = target.to_s
+      when "", Liquid::Expression::MethodLiteral # empty/blank hashes and arrays will match this
         return true if property == target || Array(property).join == target
       else
         target = target.to_s

test/test_filters.rb

@@ -918,13 +918,13 @@ class TestFilters < JekyllUnitTest
         # `{{ hash | where: 'tags', empty }}`
         assert_equal(
           [{ "tags" => {} }, { "tags" => "" }, { "tags" => nil }, { "tags" => [] }],
-          @filter.where(hash, "tags", Liquid::Expression::LITERALS["empty"])
+          @filter.where(hash, "tags", Liquid::Condition.parse_expression(nil, "empty"))
         )
 
         # `{{ `hash | where: 'tags', blank }}`
         assert_equal(
           [{ "tags" => {} }, { "tags" => "" }, { "tags" => nil }, { "tags" => [] }],
-          @filter.where(hash, "tags", Liquid::Expression::LITERALS["blank"])
+          @filter.where(hash, "tags", Liquid::Condition.parse_expression(nil, "blank"))
         )
       end
 
@@ -1151,13 +1151,13 @@ class TestFilters < JekyllUnitTest
         # `{{ hash | find: 'tags', empty }}`
         assert_equal(
           { "tags" => {} },
-          @filter.find(hash, "tags", Liquid::Expression::LITERALS["empty"])
+          @filter.find(hash, "tags", Liquid::Condition.parse_expression(nil, "empty"))
         )
 
         # `{{ `hash | find: 'tags', blank }}`
         assert_equal(
           { "tags" => {} },
-          @filter.find(hash, "tags", Liquid::Expression::LITERALS["blank"])
+          @filter.find(hash, "tags", Liquid::Condition.parse_expression(nil, "blank"))
         )
       end
 

test/test_tags.rb

@@ -42,12 +42,8 @@ class TestTags < JekyllUnitTest
   end
 
   def highlight_block_with_opts(options_string)
-    Jekyll::Tags::HighlightBlock.parse(
-      "highlight",
-      options_string,
-      Liquid::Tokenizer.new("test{% endhighlight %}\n"),
-      Liquid::ParseContext.new
-    )
+    template = Liquid::Template.parse("{% highlight #{options_string} %}test{% endhighlight %}")
+    template.root.nodelist.first
   end
 
   context "language name" do