From 744baef3a3bd4cf7e3efb2ed8faf7de5e9f72fd6 Mon Sep 17 00:00:00 2001
From: Charles Lowell <cowboyd@thefrontside.net>
Date: Mon, 13 Aug 2012 09:01:28 -0500
Subject: [PATCH] track causes of exceptions

---
 lib/v8/error.rb       | 82 +++++++++++++++++++++++++++++--------------
 spec/v8/error_spec.rb |  6 ++--
 2 files changed, 58 insertions(+), 30 deletions(-)

diff --git a/lib/v8/error.rb b/lib/v8/error.rb
index e406eae..2eef0d0 100644
--- a/lib/v8/error.rb
+++ b/lib/v8/error.rb
@@ -1,23 +1,59 @@
 module V8
-  class Error < StandardError
-
   # capture 99 stack frames on exception with normal details.
   # You can adjust these values for performance or turn of stack capture entirely
   V8::C::V8::SetCaptureStackTraceForUncaughtExceptions(true, 99, V8::C::StackTrace::kOverview)
+  class Error < StandardError
+    include Enumerable
+    attr_reader :value, :cause, :javascript_backtrace
 
-    attr_reader :value
-    def initialize(message, value)
+    def initialize(message, value, javascript_backtrace, cause = nil)
       super(message)
       @value = value
+      @cause = cause
+      @javascript_backtrace = javascript_backtrace
+    end
+
+    def causes
+      [].tap do |causes|
+        current = self
+        until current.nil? do
+          causes.push current
+          current = current.respond_to?(:cause) ? current.cause : nil
+        end
+      end
+    end
+
+    def root_cause
+      causes.last
+    end
+
+    def in_javascript?
+      causes.last.is_a? self.class
+    end
+
+    def in_ruby?
+      !in_javascript?
+    end
+
+    def multilingual_backtrace
+      causes.reduce(:backtrace => [], :ruby => -1, :javascript => -1) { |accumulator, cause|
+        ruby_frames = cause.backtrace[0..accumulator[:ruby]]
+        accumulator[:backtrace].unshift *ruby_frames
+        accumulator[:ruby] -= ruby_frames.length
+        if cause.respond_to?(:javascript_backtrace)
+          javascript_frames = cause.javascript_frames[0, accumulator[:javascript]].map(&:to_s)
+          accumulator[:backtrace].unshift *javascript_frames
+          accumulator[:javascript] -= javascript_frames.length
+        end
+      }[:backtrace]
     end
 
     module Try
       def try
-        context = V8::Context.current
         V8::C::TryCatch() do |trycatch|
           result = yield
           if trycatch.HasCaught()
-            V8::Error(trycatch.Exception())
+            raise V8::Error(trycatch)
           else
             result
           end
@@ -28,39 +64,33 @@ module V8
     module Protect
       def protect
         yield
-      rescue Football => e
-        e.kickoff!
       rescue Exception => e
-        e.extend Football
-        e.kickoff!
-      end
-    end
-
-    module Football
-      def kickoff!
-        error = V8::C::Exception::Error(message)
-        error.SetHiddenValue("rr::Football", V8::C::External::New(self))
+        error = V8::C::Exception::Error(e.message)
+        error.SetHiddenValue("rr::Cause", V8::C::External::New(e))
         V8::C::ThrowException(error)
       end
     end
 
   end
 
-  def self.Error(exception)
+  def self.Error(trycatch)
+    exception = trycatch.Exception()
     value = exception.to_ruby
-    if !exception.kind_of?(V8::C::Value)
-      raise V8::Error.new(exception.to_s, value)
+    cause = nil
+    message = if !exception.kind_of?(V8::C::Value)
+      exception.to_s
     elsif exception.IsNativeError()
-      if football = exception.GetHiddenValue("rr::Football")
-        raise football.Value()
-      else
-        raise V8::Error.new(exception.Get("message").to_ruby, value)
+      if cause = exception.GetHiddenValue("rr::Cause")
+        cause = cause.Value()
       end
+      exception.Get("message").to_ruby
     elsif exception.IsObject()
-      raise V8::Error.new(value['message'] || value.to_s, value)
+      value['message'] || value.to_s
     else
-      raise V8::Error.new(exception.ToString().to_ruby, value)
+      value.to_s
     end
+    javascript_backtrace = V8::StackTrace.new(trycatch.Message().GetStackTrace())
+    V8::Error.new(message, value, javascript_backtrace, cause)
   end
   const_set :JSError, Error
 end
\ No newline at end of file
diff --git a/spec/v8/error_spec.rb b/spec/v8/error_spec.rb
index bb3984e..65cf40d 100644
--- a/spec/v8/error_spec.rb
+++ b/spec/v8/error_spec.rb
@@ -39,16 +39,14 @@ describe V8::Error do
   end
 
   it "has a reference to the root javascript cause" do
-    pending
     throw!('"I am a String"') do |e|
       e.should_not be_in_ruby
       e.should be_in_javascript
-      e.value.should == "I am a String"
+      e.value['message'].should == "I am a String"
     end
   end
 
   it "has a reference to the root ruby cause if one exists" do
-    pending
     StandardError.new("BOOM!").tap do |bomb|
       @cxt['boom'] = lambda do
         raise bomb
@@ -58,7 +56,7 @@ describe V8::Error do
       }.should(raise_error do |raised|
         raised.should be_in_ruby
         raised.should_not be_in_javascript
-        raised.value.should be(bomb)
+        raised.root_cause.should be(bomb)
       end)
     end
   end