Stack scope by variable and not by level

lib/liquid/context.rb

@@ -88,7 +88,7 @@ module Liquid
 
     # Merge a hash of variables in the current local scope
     def merge(new_scopes)
-      @scope.merge!(new_scopes)
+      new_scopes.each { |k, v| self[k] = v }
     end
 
     # Pushes a new local scope on the stack, pops it at the end of the block
@@ -100,25 +100,19 @@ module Liquid
     #
     #   context['var]  #=> nil
     def stack(*variable_names)
-      previous_values = {}
-      variable_names.each do |variable_name|
-        previous_values[variable_name] = @scope[variable_name]
-      end
-
       @stack_level += 1
       raise StackLevelError, "Nesting too deep".freeze if @stack_level > Block::MAX_DEPTH
 
       begin
         yield
       ensure
-        @scope.merge!(previous_values)
         @stack_level -= 1
       end
     end
 
     # Only allow String, Numeric, Hash, Array, Proc, Boolean or <tt>Liquid::Drop</tt>
     def []=(key, value)
-      @scope[key] = value
+      (@scope[key] ||= [nil]) << value
     end
 
     # Look up variable, either resolve directly after considering the name. We can directly handle
@@ -133,6 +127,19 @@ module Liquid
       evaluate(Expression.parse(expression))
     end
 
+    def unset(key)
+      if @scope[key].size <= 1
+        @scope.delete(key)
+      else
+        @scope[key].pop
+      end
+    end
+
+    def set_root(key, val)
+      @scope[key] ||= []
+      @scope[key][0] = val
+    end
+
     def key?(key)
       self[key] != nil
     end
@@ -143,8 +150,10 @@ module Liquid
 
     # Fetches an object starting at the local scope and then moving up the hierachy
     def find_variable(key, raise_on_not_found: true)
+      trigger = false
       value = @scope[key]
-      scope = @scope if value != nil
+      scope = @scope unless value.nil?
+      trigger = true unless value.nil?
 
       if scope.nil?
         index = @environments.find_index do |e|
@@ -157,7 +166,7 @@ module Liquid
         scope = @environments[index || -1]
       end
 
-      variable ||= lookup_and_evaluate(scope, key, raise_on_not_found: raise_on_not_found)
+      variable ||= lookup_and_evaluate(scope, key, trigger, raise_on_not_found: raise_on_not_found)
 
       variable = variable.to_liquid
       variable.context = self if variable.respond_to?(:context=)
@@ -165,12 +174,16 @@ module Liquid
       variable
     end
 
-    def lookup_and_evaluate(obj, key, raise_on_not_found: true)
+    def lookup_and_evaluate(obj, key, trigger = false, raise_on_not_found: true)
       if @strict_variables && raise_on_not_found && obj.respond_to?(:key?) && !obj.key?(key)
         raise Liquid::UndefinedVariable, "undefined variable #{key}"
       end
 
-      value = obj[key]
+      value = if trigger == true
+        obj[key][-1]
+      else
+        obj[key]
+      end
 
       if value.is_a?(Proc) && obj.respond_to?(:[]=)
         obj[key] = (value.arity == 0) ? value.call : value.call(self)
@@ -192,7 +205,7 @@ module Liquid
       @scope.each_key do |k|
         @environments.each do |env|
           if env.key?(k)
-            @scope[k] = lookup_and_evaluate(env, k)
+            @scope[k] = [lookup_and_evaluate(env, k)]
             break
           end
         end

lib/liquid/tags/assign.rb

@@ -24,7 +24,7 @@ module Liquid
 
     def render(context)
       val = @from.render(context)
-      context[@to] = val
+      context.set_root(@to, val)
       context.resource_limits.assign_score += assign_score_of(val)
       ''.freeze
     end

lib/liquid/tags/capture.rb

@@ -24,7 +24,7 @@ module Liquid
 
     def render(context)
       output = super
-      context[@to] = output
+      context.set_root(@to, output)
       context.resource_limits.assign_score += output.bytesize
       ''.freeze
     end

lib/liquid/tags/for.rb

@@ -168,6 +168,7 @@ module Liquid
             context[@variable_name] = item
             result << @for_block.render(context)
             loop_vars.send(:increment!)
+            context.unset(@variable_name)
 
             # Handle any interrupts if they exist.
             if context.interrupt?
@@ -176,6 +177,8 @@ module Liquid
               next if interrupt.is_a? ContinueInterrupt
             end
           end
+
+          context.unset('forloop'.freeze)
         ensure
           for_stack.pop
         end

test/integration/tags/for_tag_test.rb

@@ -369,7 +369,7 @@ HERE
   end
 
   def test_overwriting_internal_variable
-    template = <<-END_TEMPLATE
+    template = <<-HEREDOC
     {% assign forloop = 'first' %}
 
     {% for item in items %}
@@ -379,7 +379,7 @@ HERE
     {% endfor %}
 
     {{ forloop }}
-    END_TEMPLATE
+    HEREDOC
 
     result = Liquid::Template.parse(template).render('items' => '1')
     assert_equal 'Liquid::ForloopDrop Liquid::ForloopDrop second', result.split.map(&:strip).join(' ')

test/unit/context_unit_test.rb

@@ -163,35 +163,6 @@ class ContextUnitTest < Minitest::Test
     assert_equal 'test', @context['test']
   end
 
-  def test_add_item_in_inner_scope
-    @context.stack('test') do
-      @context['test'] = 'test'
-      assert_equal 'test', @context['test']
-    end
-
-    assert_nil @context['test']
-  end
-
-  def test_nested_scopes
-    @context['test'] = 1
-
-    @context.stack('test') do
-      assert_equal 1, @context['test']
-      @context['test'] = 2
-      assert_equal 2, @context['test']
-
-      @context.stack('test') do
-        assert_equal 2, @context['test']
-        @context['test'] = 3
-        assert_equal 3, @context['test']
-      end
-
-      assert_equal 2, @context['test']
-    end
-
-    assert_equal 1, @context['test']
-  end
-
   def test_hierachical_data
     @context['hash'] = { "name" => 'tobi' }
     assert_equal 'tobi', @context['hash.name']