Move 'backtrace' from subr.el to backtrace.el

* lisp/subr.el (backtrace, backtrace--print-frame): Remove functions.
* lisp/emacs-lisp/backtrace.el (backtrace-backtrace): Remove function.
(backtrace): New function.
(backtrace-to-string): Make argument optional.
* doc/lispref/debugging.texi (Internals of Debugger): Update
description of 'backtrace' function.

2 files changed, 8 insertions, 23 deletions

diff --git a/lisp/emacs-lisp/backtrace.el b/lisp/emacs-lisp/backtrace.el
index 5169c305035..d162983c017 100644
--- a/lisp/emacs-lisp/backtrace.el
+++ b/lisp/emacs-lisp/backtrace.el
@@ -891,14 +891,18 @@ followed by `backtrace-print-frame', once for each stack frame."
 
 ;;; Backtrace printing
 
-(defun backtrace-backtrace ()
+;;;###autoload
+(defun backtrace ()
   "Print a trace of Lisp function calls currently active.
 Output stream used is value of `standard-output'."
-  (princ (backtrace-to-string (backtrace-get-frames 'backtrace-backtrace))))
+  (princ (backtrace-to-string (backtrace-get-frames 'backtrace)))
+  nil)
 
-(defun backtrace-to-string(frames)
+(defun backtrace-to-string(&optional frames)
   "Format FRAMES, a list of `backtrace-frame' objects, for output.
-Return the result as a string."
+Return the result as a string.  If FRAMES is nil, use all
+function calls currently active."
+  (unless frames (setq frames (backtrace-get-frames 'backtrace-to-string)))
   (let ((backtrace-fontify nil))
     (with-temp-buffer
       (backtrace-mode)
diff --git a/lisp/subr.el b/lisp/subr.el
index f8c19efc379..fbb3e49a35c 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -4687,25 +4687,6 @@ The properties used on SYMBOL are `composefunc', `sendfunc',
   (put symbol 'hookvar (or hookvar 'mail-send-hook)))
 
 
-(defun backtrace--print-frame (evald func args flags)
-  "Print a trace of a single stack frame to `standard-output'.
-EVALD, FUNC, ARGS, FLAGS are as in `mapbacktrace'."
-  (princ (if (plist-get flags :debug-on-exit) "* " "  "))
-  (cond
-   ((and evald (not debugger-stack-frame-as-list))
-    (cl-prin1 func)
-    (if args (cl-prin1 args) (princ "()")))
-   (t
-    (cl-prin1 (cons func args))))
-  (princ "\n"))
-
-(defun backtrace ()
-  "Print a trace of Lisp function calls currently active.
-Output stream used is value of `standard-output'."
-  (let ((print-level (or print-level 8))
-        (print-escape-control-characters t))
-    (mapbacktrace #'backtrace--print-frame 'backtrace)))
-
 (defun backtrace-frames (&optional base)
   "Collect all frames of current backtrace into a list.
 If non-nil, BASE should be a function, and frames before its