Re: [PATCH]: Re: Early backtrace.

[Stefan Monnier <monnier@iro.umontreal.ca>]

Alan Mackenzie [2022-01-30 11:07:32] wrote:

>> Namespace prefixes don't need to be created before we use them.
>> The point is just that `debugger-` is already used by definitions (in
>> `debug.el`) so we can reuse that space instead of messing up pristine
>> real estate.
> OK, I've called it debug-early.

Deal!

> Are there any objections to me committing this to master?

See my comments below.

>    /* If we're in batch mode, print a backtrace unconditionally to help
> -     with debugging.  Make sure to use `debug' unconditionally to not
> -     interfere with ERT or other packages that install custom
> -     debuggers.  Don't try to call the debugger while dumping or
> -     bootstrapping, it wouldn't work anyway.  */
> +     with debugging.  Make sure to use `debug-early' unconditionally
> +     to not interfere with ERT or other packages that install custom
> +     debuggers.  */

This is not your fault, but I notice that this comment doesn't explain
how we distinguish the case where we want to print a backtrace from the
case where we want to call ERT's "debugger", both of which can occur in
batch mode.

> (defalias 'debug-early-backtrace
>   #'(lambda ()
>   "Print a trace of Lisp function calls currently active.
> The output stream used is the value of `standard-output'.
>
> This is a simplified version of the standard `backtrace'
> function, intended for use in debugging the early parts
> of the build process."
>   (princ "\n")
>   (mapbacktrace
>    #'(lambda (evald func args _flags)
>        (let ((args args))
> 	 (if evald
> 	     (progn
> 	       (princ "  ")
> 	       (prin1 func)
> 	       (princ " (")
> 	       (while args
> 		 (prin1 (car args))
> 		 (setq args (cdr args))
> 		 (if args
> 		     (princ " ")))
> 	       (princ ")\n"))
> 	   (while args
> 	     (princ "  ")
> 	     (prin1 (car args))
> 	     (princ "\n")
> 	     (setq args (cdr args)))))))))
>
> (defalias 'debug-early
>   #'(lambda (&rest args)
>   "Print a trace of Lisp function calls currently active.
> The output stream used is the value of `standard-output'.
>
> There should be two ARGS, the symbol `error' and a cons of
> the error symbol and its data.
>
> This is a simplified version of `debug', intended for use
> in debugging the early parts of the build process."
>   (princ "\nError: ")
>   (prin1 (car (car (cdr args))))	; The error symbol.
>   (princ " ")
>   (prin1 (cdr (car (cdr args))))	; The error data.
>   (debug-early-backtrace)))

I'm curious: why did you split this into two functions?

> (setq debugger #'debug-early)

Could we make `debug-early` the default/initial value of `debugger` in
the C code, so that reloading `debug-early.el` can be done safely?


        Stefan