Debug on exception

[bo-tato]

Add support on the cider side to go with clojure-emacs/cider-nrepl#769
passing a negative argument to cider-eval-defun-at-point will instrument it with #dbgexn
also added some documentation to the debugger docs describing the new feature

---

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Thanks!

If you're just starting out to hack on CIDER you might find this section of its
manual extremely useful.

[bbatsov]

@yuhan0 I guess you'll take this from here, right?

[yuhan0]

How do you feel about this proposal of overloading cider-eval-defun with a negative argument?
I find that sort of API quite bad for discoverability - in my personal config I have these custom commands instead, along with similar ones for various other temporary debugging forms - basically generalizing the existing cider--prompt-and-insert-inline-dbg interface.

;; * Insert #break / #dbg reader forms
(defun +cider-insert-dbg (ex)
  "Insert #dbg reader.
If EX is non nil or called with prefix arg, insert #dbg! to break on exception.
Automatically reevaluates form if inside a defn."
  (interactive "P")
  (unless (looking-at-p "(")
    (backward-up-list))
  (cider-insert-fragile-reader-macro
   (if ex "#dbg!"
     (concat "#dbg"
             (let ((cond (cider-read-from-minibuffer "Condition: ")))
               (unless (equal "" cond)
                 (format " ^{:break/when %s}" cond))))))
  (when (clojure-top-level-form-p "defn")
    (cider-eval-defun-at-point)))

(defun +cider-insert-breakpoint (ex)
  "Insert #break reader.
If EX is non nil or called with prefix arg, insert #break! to break on exception."
  (interactive "P")
  (cider-insert-fragile-reader-macro
   (if ex "#break!"
     (concat "#break"
             (let ((cond (cider-read-from-minibuffer "Condition: ")))
               (unless (equal "" cond)
                 (format " ^{:break/when %s}" cond)))))))

[yuhan0]

A quick demo of what that looks like in practice
https://github.com/clojure-emacs/cider/assets/22216124/8e0440e4-da2c-4de0-890d-8d882185719a

[bbatsov]

How do you feel about this proposal of overloading cider-eval-defun with a negative argument?

I'm not a big fan of prefix arguments in general, but from time to time they fit in nicely. Definitely not a big fan of the negative argument, as it's probably the hardest to discover organically by users. I'm ok with adding some special commands and I guess we can have something with prefix arguments as well, for whoever prefers them, given that it adds little complexity.

The demo looks good to me.

[bbatsov]

@yuhan0 Any chance you'll have time for this soon? I think it's the only feature remaining for the next CIDER release.

[yuhan0]

Yes, I have the working code for this feature but unfortunately don't have much time over the next couple of days to work on testing / refining it into a PR. If it's a blocker for a release maybe I'll push those commits now and see if anyone can take it from there? Might be able to do something over the weekend too.

[bbatsov]

@yuhan0 No rush, there's one more blocker anyways (#3365). If you can spend some time on this over the weekend that'd be great.

I'll close this PR in favor of #3366 that you've opened just now.