Make liquid rendering optional.

Although the author of the liquid template wants to see these errors, they
probably don't want the visitor to see the liquid errors.  Probably the
best fallback when rendering the page for visitors is to render the empty
string for tags with errors.

lib/liquid/context.rb

@@ -13,15 +13,16 @@ module Liquid
   #   context['bob']  #=> nil  class Context
   class Context
     attr_reader :scopes, :errors, :registers, :environments, :resource_limits
-    attr_accessor :exception_handler
+    attr_accessor :exception_handler, :render_errors
 
-    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil)
+    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil, render_errors = true)
       @environments     = [environments].flatten
       @scopes           = [(outer_scope || {})]
       @registers        = registers
       @errors           = []
       @resource_limits  = resource_limits || ResourceLimits.new(Template.default_resource_limits)
       squash_instance_assigns_with_environments
+      @render_errors    = render_errors
 
       @this_stack_used = false
 
@@ -69,7 +70,7 @@ module Liquid
 
       errors.push(e)
       raise if exception_handler && exception_handler.call(e)
-      Liquid::Error.render(e)
+      render_errors ? Liquid::Error.render(e) : ''
     end
 
     def invoke(method, *args)

lib/liquid/template.rb

@@ -17,7 +17,7 @@ module Liquid
       locale: I18n.new
     }
 
-    attr_accessor :root
+    attr_accessor :root, :render_errors
     attr_reader :resource_limits
 
     @@file_system = BlankFileSystem.new
@@ -112,6 +112,7 @@ module Liquid
 
     def initialize
       @resource_limits = ResourceLimits.new(self.class.default_resource_limits)
+      @render_errors = true
     end
 
     # Parse source code.
@@ -163,6 +164,8 @@ module Liquid
     def render(*args)
       return ''.freeze if @root.nil?
 
+      render_errors = self.render_errors
+
       context = case args.first
       when Liquid::Context
         c = args.shift
@@ -174,11 +177,11 @@ 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, registers, @rethrow_errors, @resource_limits, render_errors)
       when Hash
-        Context.new([args.shift, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits)
+        Context.new([args.shift, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits, render_errors)
       when nil
-        Context.new(assigns, instance_assigns, registers, @rethrow_errors, @resource_limits)
+        Context.new(assigns, instance_assigns, registers, @rethrow_errors, @resource_limits, render_errors)
       else
         raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
       end