From 869dbc7ebf6cb68f0d32baf7e86f2a4fa2f14f3e Mon Sep 17 00:00:00 2001
From: Dylan Thacker-Smith <dylan.smith@shopify.com>
Date: Mon, 12 Dec 2016 10:29:09 -0500
Subject: [PATCH] feature: Allow a default exception renderer to be specified
 (#837)

This could be used to preserve the old default of rendering
non-Liquid::Error messages or for providing default behaviour like error
reporting which could be missed if the exception renderer needed to be
specified on each render.
---
 lib/liquid/context.rb                   |  5 ++---
 lib/liquid/template.rb                  |  5 +++++
 test/integration/error_handling_test.rb | 14 ++++++++++++++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/lib/liquid/context.rb b/lib/liquid/context.rb
index 2b7544b..6ba2353 100644
--- a/lib/liquid/context.rb
+++ b/lib/liquid/context.rb
@@ -27,6 +27,7 @@ module Liquid
 
       @this_stack_used = false
 
+      self.exception_renderer = Template.default_exception_renderer
       if rethrow_errors
         self.exception_renderer = ->(e) { raise }
       end
@@ -78,9 +79,7 @@ module Liquid
       e.template_name ||= template_name
       e.line_number ||= line_number
       errors.push(e)
-
-      e = exception_renderer.call(e) if exception_renderer
-      e.to_s
+      exception_renderer.call(e).to_s
     end
 
     def invoke(method, *args)
diff --git a/lib/liquid/template.rb b/lib/liquid/template.rb
index ebd8fc0..31a67e4 100644
--- a/lib/liquid/template.rb
+++ b/lib/liquid/template.rb
@@ -69,6 +69,11 @@ module Liquid
       # :error raises an error when tainted output is used
       attr_writer :taint_mode
 
+      attr_accessor :default_exception_renderer
+      Template.default_exception_renderer = lambda do |exception|
+        exception
+      end
+
       def file_system
         @@file_system
       end
diff --git a/test/integration/error_handling_test.rb b/test/integration/error_handling_test.rb
index 9d20be2..ba81861 100644
--- a/test/integration/error_handling_test.rb
+++ b/test/integration/error_handling_test.rb
@@ -211,6 +211,20 @@ class ErrorHandlingTest < Minitest::Test
     assert_equal [Liquid::InternalError], template.errors.map(&:class)
   end
 
+  def test_setting_default_exception_renderer
+    old_exception_renderer = Liquid::Template.default_exception_renderer
+    exceptions = []
+    Liquid::Template.default_exception_renderer = ->(e) { exceptions << e; '' }
+    template = Liquid::Template.parse('This is a runtime error: {{ errors.argument_error }}')
+
+    output = template.render({ 'errors' => ErrorDrop.new })
+
+    assert_equal 'This is a runtime error: ', output
+    assert_equal [Liquid::ArgumentError], template.errors.map(&:class)
+  ensure
+    Liquid::Template.default_exception_renderer = old_exception_renderer if old_exception_renderer
+  end
+
   def test_exception_renderer_exposing_non_liquid_error
     template = Liquid::Template.parse('This is a runtime error: {{ errors.runtime_error }}', line_numbers: true)
     exceptions = []