From 29dfe2aea453c40c646f1fe5c0a858d054985935 Mon Sep 17 00:00:00 2001
From: Mike Angell <mike.angell@shopify.com>
Date: Mon, 16 Sep 2019 21:42:51 +1000
Subject: [PATCH] Prevent needing to squash instance assigns

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  | 12 ------------
 lib/liquid/template.rb | 10 +++++++---
 2 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/lib/liquid/context.rb b/lib/liquid/context.rb
index daae5de..dcdbf39 100644
--- a/lib/liquid/context.rb
+++ b/lib/liquid/context.rb
@@ -33,7 +33,6 @@ module Liquid
       @strict_variables    = false
       @resource_limits     = resource_limits || ResourceLimits.new(Template.default_resource_limits)
       @base_scope_depth    = 0
-      squash_instance_assigns_with_environments
 
       self.exception_renderer = Template.default_exception_renderer
       if rethrow_errors
@@ -245,16 +244,5 @@ 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
diff --git a/lib/liquid/template.rb b/lib/liquid/template.rb
index 62250b2..286dbd2 100644
--- a/lib/liquid/template.rb
+++ b/lib/liquid/template.rb
@@ -146,6 +146,10 @@ module Liquid
       @instance_assigns ||= {}
     end
 
+    def new_outer_scope
+      @instance_assigns = {}
+    end
+
     def errors
       @errors ||= []
     end
@@ -178,11 +182,11 @@ 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, 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, 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, instance_assigns], new_outer_scope, registers, @rethrow_errors, @resource_limits)
       else
         raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
       end