Append link to bad code to backtrace when exception is SyntaxError

actionpack/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Append link to bad code to backtrace when exception is SyntaxError.
+
+    *Boris Kuznetsov*
+    
 *   Swapped the parameters of assert_equal in `assert_select` so that the
     proper values were printed correctly 
 

actionpack/lib/action_dispatch/middleware/exception_wrapper.rb

@@ -32,6 +32,8 @@ module ActionDispatch
     def initialize(env, exception)
       @env = env
       @exception = original_exception(exception)
+
+      expand_backtrace if exception.is_a?(SyntaxError) || exception.try(:original_exception).try(:is_a?, SyntaxError)
     end
 
     def rescue_template
@@ -104,5 +106,11 @@ module ActionDispatch
         end
       end
     end
+
+    def expand_backtrace
+      @exception.backtrace.unshift(
+        @exception.to_s.split("\n")
+      ).flatten! 
+    end
   end
 end

actionpack/test/dispatch/debug_exceptions_test.rb

@@ -43,6 +43,19 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
         raise ActionController::UrlGenerationError, "No route matches"
       when "/parameter_missing"
         raise ActionController::ParameterMissing, :missing_param_key
+      when "/original_syntax_error"
+        eval 'broke_syntax =' # `eval` need for raise native SyntaxError at runtime
+      when "/syntax_error_into_view"
+        begin
+          eval 'broke_syntax ='
+        rescue Exception => e
+          template = ActionView::Template.new(File.read(__FILE__),
+                                              __FILE__,
+                                              ActionView::Template::Handlers::Raw.new,
+                                              {})
+          raise ActionView::Template::Error.new(template, e)
+        end
+
       else
         raise "puke!"
       end
@@ -242,4 +255,26 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
     get "/", {}, env
     assert_operator((output.rewind && output.read).lines.count, :>, 10)
   end
+
+  test 'display backtrace when error type is SyntaxError' do
+    @app = DevelopmentApp
+
+    get '/original_syntax_error', {}, {'action_dispatch.backtrace_cleaner' => ActiveSupport::BacktraceCleaner.new}
+
+    assert_response 500
+    assert_select '#Application-Trace' do
+      assert_select 'pre code', /\(eval\):1: syntax error, unexpected/
+    end
+  end
+
+  test 'display backtrace when error type is SyntaxError wrapped by ActionView::Template::Error' do
+    @app = DevelopmentApp
+
+    get '/syntax_error_into_view', {}, {'action_dispatch.backtrace_cleaner' => ActiveSupport::BacktraceCleaner.new}
+
+    assert_response 500
+    assert_select '#Application-Trace' do
+      assert_select 'pre code', /\(eval\):1: syntax error, unexpected/
+    end
+  end
 end