Emacs Debugging Basics

Thanks. Today I learned of `debug-on-message`.

> (In case you do not know yet, here is how to type M-x toggle-debug-on-error on the keyboard: alt+x SPACE toggle-debug-on-error RETURN) `SPACE` should not be there right?

Good catch, thanks for pointing it out. Just fixed it.

`C-h f debug-on-entry` `C-h f debug`

For more in-depth debugging there is also edebug which has the usual debugger features like of stepping through code, breakpoints, watches. You need to instrument the function(s) to be debugged using `C-u C-M-x`. For macros I find the `macrostep` package very handy, it lets you interactive expand or collapse macros in their source context. Or just `M-x pp-macroexpand-last-sexp` often does the job too.

Very helpful to learn how to debug errors, thanks! What about a next post concerning how to debug performance issues?

Thanks for mentioning these. I briefly mentioned `debug-on-entry` in the end, but as to `debug`, I still don't know when to use it after reading the docstring. Would you like to elaborate on it? Thanks.

Good idea, but I don't yet have much experience about debugging performance issues myself (I did try to write a post about how not to make emacs slow while we're interacting with it), I will think about it, thanks for the suggestion.

Yes, edebug is powerful for debugging in the source code level. I did not mention it because it isn't suitable (or is over killed) for beginners. Maybe I'd write an advanced emacs/elisp debugging techniques in the future:)

Function `debug` opens the debugger; nothing more. You can put calls to `debug` at places in code where you want a breakpoint, i.e., you want to enter the debugger. Read the fine manual (and doc string) about using the debugger. In a nutshell: `d` to single-step through evaluation. `c` to skip through evaluation (i.e., just evaluate the current sexp completely, without going through its evaluation step-by-step). `q` to quit the debugger.

Got it, thanks for the detailed explanation.

For debugging init file problems, I have gotten a lot of mileage out of [elisp-bug-hunter](https://github.com/Malabarba/elisp-bug-hunter). It will automatically bisect your init file to find the problematic code. It is one of the first things I load in my init.

Wow, cool package! Gonna put a link to it in my post, thanks!