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* lisp/emacs-lisp/debug-early.el: Improve the documentation

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This commit is contained in:
Alan Mackenzie 2022-02-05 10:43:27 +00:00
parent 49192d1418
commit 9029212c86
1 changed files with 19 additions and 9 deletions
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28
lisp/emacs-lisp/debug-early.el
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@ -24,10 +24,12 @@
;;; Commentary:
;; This file dumps a backtrace on stderr when an error is thrown.
;; It has no dependencies on any Lisp libraries and is thus suitable
;; for generating backtraces in the early parts of bootstrapping. It
;; is also good for generating backtraces in batch mode in general.
;; 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 model. It was introduced in Emacs
;; 29, before which there was no backtrace available during early
;; bootstrap.
(defalias 'debug-early-backtrace
#'(lambda ()
@ -60,14 +62,22 @@ of the build process."
(defalias 'debug-early
#'(lambda (&rest args)
"Print a trace of Lisp function calls currently active.
"Print an error message with a backtrace of active Lisp function calls.
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.
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.
This is a simplified version of `debug', intended for use
in debugging the early parts of the build process."
`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superseded by `debug' after enough Lisp has been loaded to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.)"
(princ "\nError: ")
(prin1 (car (car (cdr args)))) ; The error symbol.
(princ " ")