Increase max-lisp-eval-depth adjustment while in debugger (bug#31919)

* src/eval.c (call_debugger): Increase the amount of extra Lisp
evaluation depth given to the debugger to allow it to call cl-print.
* lisp/emacs-lisp/debug.el (debugger-setup-buffer): Add a comment
to suggest updating call_debugger when changing print-level.

2 files changed, 7 insertions, 2 deletions

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index 593fab97275..821d6748821 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -322,6 +322,7 @@ That buffer should be current already."
                  (backtrace-frames 'debug)))
         (print-escape-newlines t)
         (print-escape-control-characters t)
+        ;; If you increase print-level, add more depth in call_debugger.
         (print-level 8)
         (print-length 50)
         (pos (point)))
diff --git a/src/eval.c b/src/eval.c
index ca1eb84ff3f..40cba3bb1ce 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -282,8 +282,12 @@ call_debugger (Lisp_Object arg)
   /* Do not allow max_specpdl_size less than actual depth (Bug#16603).  */
   EMACS_INT old_max = max (max_specpdl_size, count);
 
-  if (lisp_eval_depth + 40 > max_lisp_eval_depth)
-    max_lisp_eval_depth = lisp_eval_depth + 40;
+  /* The previous value of 40 is too small now that the debugger
+     prints using cl-prin1 instead of prin1.  Printing lists nested 8
+     deep (which is the value of print-level used in the debugger)
+     currently requires 77 additional frames.  See bug#31919.  */
+  if (lisp_eval_depth + 100 > max_lisp_eval_depth)
+    max_lisp_eval_depth = lisp_eval_depth + 100;
 
   /* While debugging Bug#16603, previous value of 100 was found
      too small to avoid specpdl overflow in the debugger itself.  */