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.

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
@@ -33,16 +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
+      @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
 
@@ -245,16 +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/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

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')