Addressed an issue where syntax errors generated inside an eval

method cause an Internal Server Error due to a TypeError.

In order to display the extraced source of a syntax error, we try
to locate the node id for the backtrace location. The call to
RubyVM::AbstractSyntaxTree.node_id_for_backtrace_location is expecting
a Thread::Backtrace::Location object, but we are passing a
SourceMapLocation instead.

This commit does two things:
1) it addresses the issue by making sure that we are always passing
a Thread::Backtrace::Location instead
2) it allows the development view to show the extracted source fragment

actionpack/lib/action_dispatch/middleware/exception_wrapper.rb

@@ -248,7 +248,7 @@ def initialize(location, template)
         end
 
         def spot(exc)
-          if RubyVM::AbstractSyntaxTree.respond_to?(:node_id_for_backtrace_location)
+          if RubyVM::AbstractSyntaxTree.respond_to?(:node_id_for_backtrace_location) && __getobj__.is_a?(Thread::Backtrace::Location)
             location = @template.spot(__getobj__)
           else
             location = super
@@ -273,7 +273,12 @@ def build_backtrace
 
         (@exception.backtrace_locations || []).map do |loc|
           if built_methods.key?(loc.label.to_s)
-            SourceMapLocation.new(loc, built_methods[loc.label.to_s])
+            thread_backtrace_location = if loc.respond_to?(:__getobj__)
+              loc.__getobj__
+            else
+              loc
+            end
+            SourceMapLocation.new(thread_backtrace_location, built_methods[loc.label.to_s])
           else
             loc
           end

actionpack/test/dispatch/exception_wrapper_test.rb

@@ -69,6 +69,20 @@ def backtrace
       end
     end
 
+    class_eval "def throw_syntax_error; eval %(
+      'abc' + pluralize 'def'
+    ); end", "lib/file.rb", 42
+
+    test "#source_extracts works with eval syntax error" do
+      exception = begin throw_syntax_error; rescue SyntaxError => ex; ex; end
+
+      wrapper = ExceptionWrapper.new(nil, TopErrorProxy.new(exception, 1))
+
+      assert_called_with(wrapper, :source_fragment, ["lib/file.rb", 42], returns: "foo") do
+       assert_equal [ code: "foo", line_number: 42 ], wrapper.source_extracts
+     end
+    end
+
     if defined?(ErrorHighlight) && Gem::Version.new(ErrorHighlight::VERSION) >= Gem::Version.new("0.4.0")
       test "#source_extracts works with error_highlight" do
         lineno = __LINE__

activesupport/lib/active_support/syntax_error_proxy.rb

@@ -43,7 +43,16 @@ def backtrace_locations
 
     private
       def parse_message_for_trace
-        __getobj__.to_s.split("\n")
+        if __getobj__.to_s.start_with?("(eval")
+          # If the exception is coming from a call to eval, we need to keep
+          # the path of the file in which eval was called to ensure we can
+          # return the right source fragment to show the location of the
+          # error
+          location = __getobj__.backtrace_locations[0]
+          ["#{location.path}:#{location.lineno}: #{__getobj__}"]
+        else
+          __getobj__.to_s.split("\n")
+        end
       end
   end
 end