How to show Backtrace for emacs?

Question

I encounter an error:

scala-block-indentation: Wrong type argument: number-or-marker-p, nil

Whenever I click tab for indent in scala-mode.

I don't know where goes wrong in the code but want to fix it. However, I can only see this error in *Message* buffer without details. I tried to see this error in Backtrace but didn't know how. I tried (1) -debug-init to launch emacs (2) debug-on-entry command for scala-block-indentation but neither of them works.

Does anyone have ideas about how to enable BackTrace/Debugger for this function?

Answer 1

I have not used scala under emacs to tell if this can help you. But try (setq debug-on-error t) in your .emacs, or simply do M-: (setq debug-on-error t) to try for the current emacs session only.