bug#61847: debug-early-backtrace only works some of the time.

[Stefan Monnier]

> The cause of the problem was patch
>
> commit 08108a856a544a80d11b1e9e437fe6c45e25adec
> Author: Stefan Monnier <monnier@iro.umontreal.ca>
> Date:   Fri Apr 29 22:18:09 2022 -0400
>
>     debug-early: Print bytecode in a more manageable way
>
>     * lisp/emacs-lisp/debug-early.el (debug-early-backtrace):
>     Escape newlines to and bytecodes to make backtraces slightly more
>     readable.  Use `cl-prin1` when available.
>
> , which made debug-early.el dependent on arbitrarily nested Lisp code, in
> violation of its explicitly stated design goal to have _no_ dependence on
> Lisp code.  Some of this Lisp simply fails to load.

Indeed (fboundp 'cl-prin1) was too optimistic a test since it just
checks whether we're before loading `loaddef.el` or after it, but
`cl-prin1` uses more (preloaded) features such as those provided by
`cl-generic` which is only loaded later.

> It's not clear why the patch was applied.

To get more readable backtraces when used after bootstrapping (as well as
in the later phases of bootstrapping).

> I propose fixing the bug by restoring the code to having no such
> dependencies with the following patch:

How 'bout the patch below instead.
Maybe we should instead try and check whether we're after the bootstrap
(not sure what would be the corresponding test).


        Stefan


diff --git a/lisp/emacs-lisp/debug-early.el b/lisp/emacs-lisp/debug-early.el
index 395498f2206..65770a9c1d9 100644
--- a/lisp/emacs-lisp/debug-early.el
+++ b/lisp/emacs-lisp/debug-early.el
@@ -46,10 +46,13 @@ 'debug-early-backtrace
             (print-escape-control-characters t)
             (print-escape-nonascii t)
             (prin1 (if (and (fboundp 'cl-prin1)
+                            (fboundp 'cl-defmethod)
                             ;; If we're being called while
                             ;; bootstrapping, we won't be able to load
                             ;; cl-print.
-                            (require 'cl-print nil t))
+                            (condition-case nil
+                                (require 'cl-print nil t)
+                              (error nil)))
                        #'cl-prin1
                      #'prin1)))
         (mapbacktrace