Attach backtrace to MultipleErrors as well

Author: pitr-ch

lib/concurrent/promises.rb

@@ -958,7 +958,9 @@ def exception(*args)
         raise Concurrent::Error, 'it is not rejected' unless rejected?
         reason = Array(internal_state.reason).flatten.compact
         if reason.size > 1
-          Concurrent::MultipleErrors.new reason
+          ex = Concurrent::MultipleErrors.new reason
+          ex.set_backtrace(caller)
+          ex
         else
           ex = reason[0].clone.exception(*args)
           ex.set_backtrace Array(ex.backtrace) + caller

spec/concurrent/edge/promises_spec.rb

@@ -468,6 +468,25 @@ def behaves_as_delay(delay, value)
       end
       expect(future(0, &body).run.reason.message).to eq '5'
     end
+
+    it 'can be risen when rejected' do
+      future    = rejected_future TypeError.new
+      backtrace = caller; exception = raise future rescue $!
+      expect(exception).to be_a TypeError
+      expect(exception.backtrace[2..-1]).to eq backtrace
+
+      exception = TypeError.new
+      exception.set_backtrace(first_backtrace = %W[/a /b /c])
+      future    = rejected_future exception
+      backtrace = caller; exception = raise future rescue $!
+      expect(exception).to be_a TypeError
+      expect(exception.backtrace - exception.backtrace[3..4]).to eq(first_backtrace + backtrace)
+
+      future    = rejected_future(TypeError.new) & rejected_future(TypeError.new)
+      backtrace = caller; exception = raise future rescue $!
+      expect(exception).to be_a Concurrent::MultipleErrors
+      expect(exception.backtrace[2..-1]).to eq backtrace
+    end
   end
 
   describe 'interoperability' do