Exception handling for humans

Ability to pass exception_handler as a block to #render
and provide whatever behavior you want on handling exceptions

https://github.com/Shopify/liquid/pull/254

History.md

@@ -3,6 +3,7 @@
 ## 3.0.0 / not yet released / branch "master"
 
 * ...
+* Add exception_handler feature, see #397 and #254 [Bogdan Gusiev, bogdan and Florian Weingarten, fw42]
 * Optimize variable parsing to avoid repeated regex evaluation during template rendering #383 [Jason Hiltz-Laforge, jasonhl]
 * Optimize checking for block interrupts to reduce object allocation #380 [Jason Hiltz-Laforge, jasonhl] 
 * Properly set context rethrow_errors on render! #349 [Thierry Joyal, tjoyal]

lib/liquid/context.rb

@@ -14,8 +14,7 @@ module Liquid
   #   context['bob']  #=> nil  class Context
   class Context
     attr_reader :scopes, :errors, :registers, :environments, :resource_limits
-
-    attr_accessor :rethrow_errors
+    attr_accessor :exception_handler
 
     SQUARE_BRACKETED = /\A\[(.*)\]\z/m
 
@@ -24,10 +23,13 @@ module Liquid
       @scopes          = [(outer_scope || {})]
       @registers       = registers
       @errors          = []
-      @rethrow_errors  = rethrow_errors
       @resource_limits = (resource_limits || {}).merge!({ :render_score_current => 0, :assign_score_current => 0 })
       squash_instance_assigns_with_environments
 
+      if rethrow_errors
+        self.exception_handler = ->(e) { true }
+      end
+
       @interrupts = []
       @filters = []
       @parsed_variables = Hash.new{ |cache, markup| cache[markup] = variable_parse(markup) } 
@@ -91,7 +93,8 @@ module Liquid
 
     def handle_error(e)
       errors.push(e)
-      raise if @rethrow_errors
+
+      raise if exception_handler && exception_handler.call(e)
 
       case e
       when SyntaxError
@@ -300,5 +303,4 @@ module Liquid
         end
       end # squash_instance_assigns_with_environments
   end # Context
-
 end # Liquid

lib/liquid/template.rb

@@ -142,7 +142,11 @@ module Liquid
       context = case args.first
       when Liquid::Context
         c = args.shift
-        c.rethrow_errors = true if @rethrow_errors
+
+        if @rethrow_errors
+          c.exception_handler = ->(e) { true }
+        end
+
         c
       when Liquid::Drop
         drop = args.shift
@@ -167,6 +171,9 @@ module Liquid
           context.add_filters(options[:filters])
         end
 
+        if options[:exception_handler]
+          context.exception_handler = options[:exception_handler]
+        end
       when Module
         context.add_filters(args.pop)
       when Array

test/integration/template_test.rb

@@ -153,4 +153,18 @@ class TemplateTest < Test::Unit::TestCase
     end
     assert_equal 'ruby error in drop', e.message
   end
+
+  def test_exception_handler_doesnt_reraise_if_it_returns_false
+    exception = nil
+    Template.parse("{{ 1 | divided_by: 0 }}").render({}, exception_handler: ->(e) { exception = e; false })
+    assert exception.is_a?(ZeroDivisionError)
+  end
+
+  def test_exception_handler_does_reraise_if_it_returns_true
+    exception = nil
+    assert_raises(ZeroDivisionError) do
+      Template.parse("{{ 1 | divided_by: 0 }}").render({}, exception_handler: ->(e) { exception = e; true })
+    end
+    assert exception.is_a?(ZeroDivisionError)
+  end
 end