About using the debuggers

[mortang2410]

Hi. I am new to Doom Emacs, though I had used Emacs beore years ago. I see that using the various debuggers in Doom Emacs is somewhat confusing (at least for me I suppose). The included documentation for :tools debugger is rather sparse with unwritten parts. It mentions both dap-mode and DAPE, which are two different things. So I am sharing some of what I have figured out through trial and error, and I hope people could tell me whatever I get wrong. More tips would also be appreciated. Hopefully it will help others, and the documentation will be filled out soon.

• How to use debugger to debug emacs lisp:
  • Set debug-on-entry for a function to debug and then run/eval any elisp expression. Unfortunately debugger doesn't correspond with source (edebug uses source). Also don't turn on debugger mode on the source file (it is for the debugger backtrace buffer). In the debugger backtrace buffer, press d or j to continue. We can backtrace-toggle-locals to show locals of a specific function / context. For some limited symbols we can use backtrace-help-follow-symbol to jump to source.
• How to use edebug to debug emacs lisp:
  • Need to set edebug-instrument-defun-on for functions you want to monitor. Then run/eval any expression with gR. edebug works like debug above, but also shows which line of code in the source you're on. Press n in the source file to make one more step. Press d in the source file to see backtrace buffer, where backtrace-toggle-locals also works. Press q in source file to quit edebug.
• How to use DAPE to debug C/C++:
  • Doom docs say +lsp :: is a deprecated flag along with dap-mode and dap-ui, and that it requires :tools lsp (not compatible with Eglot). I am not sure what this means, but I suspect that dap-mode and dap-ui should no longer be used. And the :tools debugger perhaps used to be :tools debugger + lsp (but is no longer). Nowadays we enable both debugger and lsp under :tools in init.el.
    • Eglot is Emacs' built-in LSP client, and it seems to be an alternative to lsp-mode. Only one can be active at a time for any programming language. Check doom docs for each language to see how to choose which with flags.
  • Run dape with M-x in a C file, and you will be asked for the "adapter" command. Example: assuming the compile command is cc -g main.c -o main.out (output with debug symbols), a correctly formatted adapter command is
    lldb-dap :program "/Users/John/programming/C_testing/main.out" :cwd "/Users/John/programming/C_testing/" where you provide the correct :program and :cwd (current working directory). Remember to set breakpoints with dape-breakpoint-toggle.