make a pass at the changes for implementing issue-781 integrating pkg/errors

[maleck13]

@raphael This is a pass at the changes I proposed for issue-781 #781

One concern I have here is backwards compatibility. If users are relying on type checks for errors they will stop working.
For example if they were relying on checks like

if err, ok := err.(goa.ServiceError); ok {
}

From a usability point of view there is no difference however. A user of goa can still do something like

return goa.ErrInternal("something strange")

and it will work as expected except now you will see a trace in the logs

[raphael]

Thank you the PR looks great! I was thinking we would let the user call errors.Wrap themselves. This way they can provide a meaningful message and only wrap errors they care to wrap. This also helps with the backwards compatibility issue (since the type test is actually documented in the Error Handling docs). There could be a comment in the middleware header explaining that it will take care of logging the callstack if the error is wrapped.

[maleck13]

@raphael Thanks for feedback. I will look at updating based on your comment

[maleck13]

@raphael Made the changes that I think address your comment. I added a test based on the other error_handler tests and on some of the logging tests. I am not particularly familiar with the test framework so not sure I have implemented the test as would be expected. Happy for any feedback

[raphael]

Thank you! the changes look good. I left one comment related to how the logging of uncaught error is done but other than that LGTM.

[maleck13]

@raphael do you normally squash commits before merging or are these separate commits ok?

[raphael]

Yes I'll squash the commits. Is this ready for merge?

[maleck13]

👍

[raphael]

Thank you! do you think you could create a PR against the v1 branch as well?

[maleck13]

@raphael absolutely happy to