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;;; debug-early.el --- Dump a Lisp backtrace without frills -*- lexical-binding: t; -*-
;; Copyright (C) 2022-2025 Free Software Foundation, Inc.
;; Author: Alan Mackenzie <acm@muc.de>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: internal, backtrace, bootstrap.
;; Package: emacs
;; This file is part of GNU Emacs.
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; This file dumps a backtrace on stderr when an error is thrown. It
;; has no dependencies on any Lisp libraries and is thus used for
;; generating backtraces for bugs in the early parts of bootstrapping.
;; It is also always used in batch mode. It was introduced in Emacs
;; 29, before which there was no backtrace available during early
;; bootstrap.
;;; Code:
;; For bootstrap reasons, we cannot use any macros here since they're
;; not defined yet.
(defalias 'debug-early-backtrace
#'(lambda (&optional base)
"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")
(let ((print-escape-newlines t)
(print-escape-control-characters t)
(print-escape-nonascii t)
(prin1 (if (and (fboundp 'cl-prin1)
(fboundp 'cl-defmethod) ;Used by `cl-print'.
(condition-case nil
(require 'cl-print)
(error nil)))
#'cl-prin1
#'prin1))
(first t))
(mapbacktrace
#'(lambda (evald func args _flags)
(if first
;; The first is the debug-early entry point itself.
(setq first nil)
(let ((args args))
(if evald
(progn
(princ " ")
(funcall prin1 func)
(princ "("))
(progn
(princ " (")
(setq args (cons func args))))
(if args
(while (progn
(funcall prin1 (car args))
(setq args (cdr args)))
(princ " ")))
(princ ")\n"))))
base))))
(defalias 'debug--early
#'(lambda (error base)
(princ "\nError: ")
(prin1 (car error)) ; The error symbol.
(princ " ")
(prin1 (cdr error)) ; The error data.
(debug-early-backtrace base)))
(defalias 'debug-early ;Called from C.
#'(lambda (&rest args)
"Print an error message with a backtrace of active Lisp function calls.
The output stream used is the value of `standard-output'.
The Emacs core calls this function after an error has been
signaled, and supplies two ARGS. These are the symbol
`error' (which is ignored) and a cons of the error symbol and the
error data.
`debug-early' is a simplified version of `debug', and is
available during the early parts of the build process. It is
superseded by `debug' after enough Lisp has been loaded to
support the latter, except in batch mode which always uses
`debug-early'.
\(In versions of Emacs prior to Emacs 29, no backtrace was
available before `debug' was usable.)"
(debug--early (car (cdr args)) #'debug-early))) ; The error object.
(defalias 'debug-early--handler ;Called from C.
#'(lambda (err)
(if backtrace-on-error-noninteractive
(debug--early err #'debug-early--handler))))
(defalias 'debug-early--muted ;Called from C.
#'(lambda (err)
(save-current-buffer
(set-buffer (get-buffer-create "*Redisplay-trace*"))
(goto-char (point-max))
(if (bobp) nil
(let ((separator "\n\n\n\n"))
(save-excursion
;; The C code tested `backtrace_yet', instead we
;; keep a max of 10 backtraces.
(if (search-backward separator nil t 10)
(delete-region (point-min) (match-end 0))))
(insert separator)))
(insert "-- Caught at " (current-time-string) "\n")
(let ((standard-output (current-buffer)))
(debug--early err #'debug-early--muted))
(setq delayed-warnings-list
(cons '(error "Error in a redisplay Lisp hook. See buffer *Redisplay-trace*")
delayed-warnings-list)))))
;;; debug-early.el ends here.
|
