Randy Ridenour has an interesting post about debugging your init file. The main problem, he says, is that he sometimes makes a change that results in unbalanced parentheses. Often he doesn’t discover this until the next time he reboots Emacs, something he doesn’t do often.
He says that his usual method for finding the problem was to do what amounts to a binary search on his init file: He comments out half the init file. If the problem occurs, he repeats the process with the commented potion; otherwise he continues with the uncommented half. But then he discovered the built-in function check-parens that checks for unbalanced delimiters in the current buffer. That’s a nifty solution to Ridenour’s problem that I didn’t know about. Another tool in the toolbox.
The other thing about his post is that it reminded me of a package I wrote about in 2015 from Artur Malabarba: elisp-bug-hunter. I haven’t used it in a while but every time I do, it works perfectly and invariably finds the error often without any further action. What it does is automate the binary search that Ridenour used to hunt down his unbalanced parentheses but it works for any problem.
If the problem throws an error, elisp-bug-hunter will find it without any user input but for more complicated situations, you can specify a predicate to indicate whether the current run succeeded or not. I load it early in my init so it will be available if there is a problem.
So the take away from this post is two really useful debugging tools: check-parens for finding unbalanced delimiters and elisp-debug-hunter. Everyone should know these tools.