>From f4a9c861f2b14f9958925d328c7ce19f6eca0e2a Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sun, 11 Jun 2017 09:51:38 -0400
Subject: [PATCH v4 5/6] Hide byte code in backtraces (Bug#6991)

* lisp/emacs-lisp/debug.el (debugger-print-function): New defcustom,
defaulting to `cl-print'.
(debugger-insert-backtrace): Use it.
* etc/NEWS: Announce it.
---
 etc/NEWS                 |  5 +++++
 lisp/emacs-lisp/debug.el | 15 ++++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index c7a5674e51..21510fe539 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -320,6 +320,11 @@ questions, with a handy way to display help texts.
 all call stack frames in a Lisp backtrace buffer as lists.  Both
 debug.el and edebug.el have been updated to heed to this variable.
 
+---
+** Values in call stack frames are now displayed using 'cl-prin1'.
+The old behaviour of using 'prin1' can be restored by customizing the
+new option 'debugger-print-function'.
+
 +++
 ** The new variable 'x-ctrl-keysym' has been added to the existing
 roster of X keysyms.  It can be used in combination with another
diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index effe7f0cb3..78e29c4f17 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -49,6 +49,12 @@ (defcustom debugger-batch-max-lines 40
   :group 'debugger
   :version "21.1")
 
+(defcustom debugger-print-function #'cl-prin1
+  "Function used to print values in the debugger backtraces."
+  :type 'function
+  :options '(cl-prin1 prin1)
+  :version "26.1")
+
 (defcustom debugger-bury-or-kill 'bury
   "What to do with the debugger buffer when exiting `debug'.
 The value affects the behavior of operations on any window
@@ -265,10 +271,13 @@ (defun debug (&rest args)
       debugger-value)))
 
 
+(defvar cl-print-compiled-button)
+
 (defun debugger-insert-backtrace (frames do-xrefs)
   "Format and insert the backtrace FRAMES at point.
 Make functions into cross-reference buttons if DO-XREFS is non-nil."
   (let ((standard-output (current-buffer))
+        (cl-print-compiled-button t)
         (eval-buffers eval-buffer-list))
     (require 'help-mode)     ; Define `help-function-def' button type.
     (pcase-dolist (`(,evald ,fun ,args ,flags) frames)
@@ -278,10 +287,10 @@ (defun debugger-insert-backtrace (frames do-xrefs)
             (fun-pt (point)))
         (cond
          ((and evald (not debugger-stack-frame-as-list))
-          (prin1 fun)
-          (if args (prin1 args) (princ "()")))
+          (funcall debugger-print-function fun)
+          (if args (funcall debugger-print-function args) (princ "()")))
          (t
-          (prin1 (cons fun args))
+          (funcall debugger-print-function (cons fun args))
           (cl-incf fun-pt)))
         (when fun-file
           (make-text-button fun-pt (+ fun-pt (length (symbol-name fun)))
-- 
2.11.1