Tidy instance variables

Instead of needing to squash instance assigns, we instead just put them at the bottom of the enviornment stack.

This simplifies the code base and gains extra performance by not needing to loop over scopes and environments.

Gemfile

@@ -20,6 +20,6 @@ group :test do
   gem 'rubocop-performance', require: false
 
   platform :mri, :truffleruby do
-    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'liquid-tag'
+    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'master'
   end
 end

README.md

@@ -106,3 +106,9 @@ template = Liquid::Template.parse("{{x}} {{y}}")
 template.render!({ 'x' => 1}, { strict_variables: true })
 #=> Liquid::UndefinedVariable: Liquid error: undefined variable y
 ```
+
+### Usage tracking
+
+To help track usages of a feature or code path in production, we have released opt-in usage tracking. To enable this, we provide an empty `Liquid:: Usage.increment` method which you can customize to your needs. The feature is well suited to https://github.com/Shopify/statsd-instrument. However, the choice of implementation is up to you.
+
+Once you have enabled usage tracking, we recommend reporting any events through Github Issues that your system may be logging. It is highly likely this event has been added to consider deprecating or improving code specific to this event, so please raise any concerns.

lib/liquid.rb

@@ -75,6 +75,7 @@ require 'liquid/utils'
 require 'liquid/tokenizer'
 require 'liquid/parse_context'
 require 'liquid/partial_cache'
+require 'liquid/usage'
 
 # Load all the tags of the standard library
 #

lib/liquid/context.rb

@@ -21,9 +21,7 @@ module Liquid
     end
 
     def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil, static_registers = {}, static_environments = {})
-      @environments = [environments]
-      @environments.flatten!
-
+      @environments        = environments.is_a?(Array) ? environments : [environments]
       @static_environments = [static_environments].flat_map(&:freeze).freeze
       @scopes              = [(outer_scope || {})]
       @registers           = registers
@@ -33,18 +31,14 @@ module Liquid
       @strict_variables    = false
       @resource_limits     = resource_limits || ResourceLimits.new(Template.default_resource_limits)
       @base_scope_depth    = 0
-      squash_instance_assigns_with_environments
-
-      @this_stack_used = false
+      @interrupts          = []
+      @filters             = []
+      @global_filter       = nil
 
       self.exception_renderer = Template.default_exception_renderer
       if rethrow_errors
         self.exception_renderer = ->(_e) { raise }
       end
-
-      @interrupts = []
-      @filters = []
-      @global_filter = nil
     end
     # rubocop:enable Metrics/ParameterLists
 
@@ -122,19 +116,11 @@ module Liquid
     #   end
     #
     #   context['var]  #=> nil
-    def stack(new_scope = nil)
-      old_stack_used = @this_stack_used
-      if new_scope
-        push(new_scope)
-        @this_stack_used = true
-      else
-        @this_stack_used = false
-      end
-
+    def stack(new_scope = {})
+      push(new_scope)
       yield
     ensure
-      pop if @this_stack_used
-      @this_stack_used = old_stack_used
+      pop
     end
 
     # Creates a new context inheriting resource limits, filters, environment etc.,
@@ -162,10 +148,6 @@ module Liquid
 
     # Only allow String, Numeric, Hash, Array, Proc, Boolean or <tt>Liquid::Drop</tt>
     def []=(key, value)
-      unless @this_stack_used
-        @this_stack_used = true
-        push({})
-      end
       @scopes[0][key] = value
     end
 
@@ -259,16 +241,5 @@ module Liquid
     rescue Liquid::InternalError => exc
       exc
     end
-
-    def squash_instance_assigns_with_environments
-      @scopes.last.each_key do |k|
-        @environments.each do |env|
-          if env.key?(k)
-            scopes.last[k] = lookup_and_evaluate(env, k)
-            break
-          end
-        end
-      end
-    end # squash_instance_assigns_with_environments
   end # Context
 end # Liquid

lib/liquid/standardfilters.rb

@@ -421,6 +421,7 @@ module Liquid
 
     def default(input, default_value = ''.freeze)
       if !input || input.respond_to?(:empty?) && input.empty?
+        Usage.increment("default_filter_received_false_value") if input == false # See https://github.com/Shopify/liquid/issues/1127
         default_value
       else
         input

lib/liquid/tags/case.rb

@@ -37,16 +37,14 @@ module Liquid
     end
 
     def render_to_output_buffer(context, output)
-      context.stack do
-        execute_else_block = true
+      execute_else_block = true
 
-        @blocks.each do |block|
-          if block.else?
-            block.attachment.render_to_output_buffer(context, output) if execute_else_block
-          elsif block.evaluate(context)
-            execute_else_block = false
-            block.attachment.render_to_output_buffer(context, output)
-          end
+      @blocks.each do |block|
+        if block.else?
+          block.attachment.render_to_output_buffer(context, output) if execute_else_block
+        elsif block.evaluate(context)
+          execute_else_block = false
+          block.attachment.render_to_output_buffer(context, output)
         end
       end
 

lib/liquid/tags/cycle.rb

@@ -34,25 +34,23 @@ module Liquid
     def render_to_output_buffer(context, output)
       context.registers[:cycle] ||= {}
 
-      context.stack do
-        key = context.evaluate(@name)
-        iteration = context.registers[:cycle][key].to_i
+      key = context.evaluate(@name)
+      iteration = context.registers[:cycle][key].to_i
 
-        val = context.evaluate(@variables[iteration])
+      val = context.evaluate(@variables[iteration])
 
-        if val.is_a?(Array)
-          val = val.join
-        elsif !val.is_a?(String)
-          val = val.to_s
-        end
-
-        output << val
-
-        iteration += 1
-        iteration  = 0 if iteration >= @variables.size
-        context.registers[:cycle][key] = iteration
+      if val.is_a?(Array)
+        val = val.join
+      elsif !val.is_a?(String)
+        val = val.to_s
       end
 
+      output << val
+
+      iteration += 1
+      iteration  = 0 if iteration >= @variables.size
+      context.registers[:cycle][key] = iteration
+
       output
     end
 

lib/liquid/tags/if.rb

@@ -40,11 +40,9 @@ module Liquid
     end
 
     def render_to_output_buffer(context, output)
-      context.stack do
-        @blocks.each do |block|
-          if block.evaluate(context)
-            return block.attachment.render_to_output_buffer(context, output)
-          end
+      @blocks.each do |block|
+        if block.evaluate(context)
+          return block.attachment.render_to_output_buffer(context, output)
         end
       end
 

lib/liquid/tags/ifchanged.rb

@@ -1,14 +1,12 @@
 module Liquid
   class Ifchanged < Block
     def render_to_output_buffer(context, output)
-      context.stack do
-        block_output = ''
-        super(context, block_output)
+      block_output = ''
+      super(context, block_output)
 
-        if block_output != context.registers[:ifchanged]
-          context.registers[:ifchanged] = block_output
-          output << block_output
-        end
+      if block_output != context.registers[:ifchanged]
+        context.registers[:ifchanged] = block_output
+        output << block_output
       end
 
       output

lib/liquid/tags/unless.rb

@@ -7,18 +7,16 @@ module Liquid
   #
   class Unless < If
     def render_to_output_buffer(context, output)
-      context.stack do
-        # First condition is interpreted backwards ( if not )
-        first_block = @blocks.first
-        unless first_block.evaluate(context)
-          return first_block.attachment.render_to_output_buffer(context, output)
-        end
+      # First condition is interpreted backwards ( if not )
+      first_block = @blocks.first
+      unless first_block.evaluate(context)
+        return first_block.attachment.render_to_output_buffer(context, output)
+      end
 
-        # After the first condition unless works just like if
-        @blocks[1..-1].each do |block|
-          if block.evaluate(context)
-            return block.attachment.render_to_output_buffer(context, output)
-          end
+      # After the first condition unless works just like if
+      @blocks[1..-1].each do |block|
+        if block.evaluate(context)
+          return block.attachment.render_to_output_buffer(context, output)
         end
       end
 

lib/liquid/template.rb

@@ -143,7 +143,12 @@ module Liquid
     end
 
     def instance_assigns
-      @instance_assigns ||= {}
+      @instance_assigns ||= []
+    end
+
+    def new_outer_scope
+      @instance_assigns.unshift(last = {})
+      last
     end
 
     def errors
@@ -178,11 +183,11 @@ module Liquid
         c
       when Liquid::Drop
         drop = args.shift
-        drop.context = Context.new([drop, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits)
+        drop.context = Context.new([drop, assigns].concat(instance_assigns), new_outer_scope, registers, @rethrow_errors, @resource_limits)
       when Hash
-        Context.new([args.shift, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits)
+        Context.new([args.shift, assigns].concat(instance_assigns), new_outer_scope, registers, @rethrow_errors, @resource_limits)
       when nil
-        Context.new(assigns, instance_assigns, registers, @rethrow_errors, @resource_limits)
+        Context.new([assigns].concat(instance_assigns), new_outer_scope, registers, @rethrow_errors, @resource_limits)
       else
         raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
       end

lib/liquid/usage.rb

@@ -0,0 +1,6 @@
+module Liquid
+  module Usage
+    def self.increment(name)
+    end
+  end
+end

test/integration/template_test.rb

@@ -42,6 +42,18 @@ class TemplateTest < Minitest::Test
     assert_equal 'from instance assigns', t.parse("{{ foo }}").render!
   end
 
+  def test_instance_assigns_persist_on_same_template_object_between_many_parses
+    t = Template.new
+    assert_equal 'from instance assigns', t.parse("{% assign foo = 'from instance assigns' %}{{ foo }}").render!
+    assert_equal 'from instance assigns', t.parse("{{ foo }}").render!
+    assert_equal 'from instance assigns', t.parse("{{ foo }}").render!
+    assert_equal 'from instance assigns', t.parse("{{ foo }}").render!
+    assert_equal 'from instance assigns second', t.parse("{% assign foo = 'from instance assigns second' %}{{ foo }}").render!
+    assert_equal 'from instance assigns second', t.parse("{{ foo }}").render!
+    assert_equal 'from instance assigns second', t.parse("{{ foo }}").render!
+    assert_equal 'from instance assigns second', t.parse("{{ foo }}").render!
+  end
+
   def test_warnings_is_not_exponential_time
     str = "false"
     100.times do
@@ -58,6 +70,14 @@ class TemplateTest < Minitest::Test
     assert_equal 'foofoo', t.render!
   end
 
+  def test_instance_assigns_persist_on_same_template_parsing_between_many_renders
+    t = Template.new.parse("{{ foo }}{% assign foo = 'foo' %}{{ foo }}")
+    assert_equal 'foo', t.render!
+    assert_equal 'foofoo', t.render!
+    assert_equal 'foofoo', t.render!
+    assert_equal 'foofoo', t.render!
+  end
+
   def test_custom_assigns_do_not_persist_on_same_template
     t = Template.new
     assert_equal 'from custom assigns', t.parse("{{ foo }}").render!('foo' => 'from custom assigns')