Indented code cannot be debugged in-source

[yuhan0]

Expected behavior

Executing cider-debug-defun-at-point (C-u C-M-x) should work in source for forms in an indented comment block when clojure-toplevel-inside-comment-form is true.

(comment
  (inc (inc 0))
  )

More generally, this occurs when evaluating any indented form tagged with #dbg

(do
  #dbg (str (inc 0)) ;; cider-eval-last-sexp here
  ...)

Actual behavior

The source "cannot be found" and a temporary debug buffer is created.

Steps to reproduce the problem

place cursor at | and eval last sexp

(do
  #dbg (str (inc 0)) | 
  ...)

Solution

After some detective work I found the underlying issue to be the difference in column indexing between Emacs (0-indexed) and Clojure (1-indexed).

The outgoing conversion to 1-indexing happens in cider-interactive-eval, using the function cider-column-number-at-pos, so nrepl messages are sent as 1-indexed columns.

cider/cider-util.el

Line 757 in 1911c47

(defun cider-column-number-at-pos (pos)

However for incoming responses, this line in cider-nrepl causes only toplevel forms (column = 1) to be converted to 0-indexing , and no further processing is done client-side.
clojure-emacs/cider-nrepl@7660eb7#diff-0d65c570bef3dbf4640690a252e06f28R340

When column != 1 this causes an off-by-one error and the cider-debug code thinks the source has been edited.

I think the proper solution to this would be to remove the above line in cider-nrepl and offset the 1-indexed response in Emacs. This may break other clients, in particular Calva.

Environment & Version information

CIDER version information

;; CIDER 0.25.0snapshot, nREPL 0.7.0
;; Clojure 1.10.1, Java 14.0.1

Emacs version

26.3

Operating system

macOS 10.14

[yuhan0]

if the above solution looks alright I can open PRs in both repos to fix it.

[bbatsov]

Yeah, I think the proposed solution is reasonable.

[bbatsov]

//cc @PEZ

[PEZ]

Thanks for the heads-up! I'll consult with @bpringe about wether Calva is vulnerable, and how we can mitigate. When will the change in cider-nrepl be released?

[bbatsov]

I did it already - 0.25.2.

[bpringe]

I believe I accounted for this in Calva already, maybe even accidentally 😄. I tested Calva with this scenario with cider-nrepl before 0.25.2 and with it and it works as expected. 🎉

[bbatsov]

Great!