recursively parse brackets on variable lookup

lib/liquid.rb

@@ -41,7 +41,7 @@ module Liquid
   AnyStartingTag              = /#{TagStart}|#{VariableStart}/o
   PartialTemplateParser       = /#{TagStart}.*?#{TagEnd}|#{VariableStart}.*?#{VariableIncompleteEnd}/om
   TemplateParser              = /(#{PartialTemplateParser}|#{AnyStartingTag})/om
-  VariableParser              = /\[[^\]]+\]|#{VariableSegment}+\??/o
+  VariableParser              = /\[(?:[^\[\]]+|\g<0>)*\]|#{VariableSegment}+\??/o
 
   RAISE_EXCEPTION_LAMBDA = ->(_e) { raise }
 

test/integration/variable_test.rb

@@ -135,4 +135,26 @@ class VariableTest < Minitest::Test
   def test_raw_value_variable
     assert_template_result('bar', '{{ [key] }}', { 'key' => 'foo', 'foo' => 'bar' })
   end
+
+  def test_dynamic_find_var_with_drop
+    assert_template_result(
+      'bar',
+      '{{ [list[settings.zero]] }}',
+      {
+        'list' => ['foo'],
+        'settings' => SettingsDrop.new("zero" => 0),
+        'foo' => 'bar',
+      }
+    )
+
+    assert_template_result(
+      'foo',
+      '{{ [list[settings.zero]["foo"]] }}',
+      {
+        'list' => [{ 'foo' => 'bar' }],
+        'settings' => SettingsDrop.new("zero" => 0),
+        'bar' => 'foo',
+      }
+    )
+  end
 end

test/test_helper.rb

@@ -125,6 +125,17 @@ class ThingWithToLiquid
   end
 end
 
+class SettingsDrop < Liquid::Drop
+  def initialize(settings)
+    super()
+    @settings = settings
+  end
+
+  def liquid_method_missing(key)
+    @settings[key]
+  end
+end
+
 class IntegerDrop < Liquid::Drop
   def initialize(value)
     super()