Debug Emacs Lisp code the hard way

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I met some issue when using helm several days ago.

With the help from Michael Heerdegen, I can locate the line error message is dumped.

But the problem is I cannot get the backtrace at all.

So I insert some backtrace printing code above that line and "M-x eval-buffer":

(with-output-to-temp-buffer "backtrace-output"
  (let ((var 1))
      (setq var (eval '(progn
                         (1+ var)
                         (list 'testing (backtrace))))))))

It turns out that some third party package I installed changes the emacs variable "display-buffer-function". I guess that's why the backtrace is blocked. Because backtrace is usually dumped into a backtrace buffer. And backtrace buffer's is actually influenced by the variable.

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