There are cases Emacs wont print stack traces on error
How can I make elisp print a stack trace from my own code? (into the stdout/stderr for example)
Something like Python's traceback:
import traceback
traceback.print_exc()
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Which cases? What's the use case of the function? (how Emacs (or elisp) can print to stdout/stderr?) – xuchunyang Apr 9 '20 at 8:31
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I wanted to avoid getting into the use-case because I'd just like to get the stack-trace in any context where I'm running elisp and not focus on the particular case why. I've run into a few cases where stack traces are totally ignored, asked about it here, and there wasn't a straightforward answer. – ideasman42 Apr 9 '20 at 10:53
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I'm not sure just what you're asking, but does using function backtrace in your code, at the place where you want to see a backtrace, help? C-h f says:
backtraceis a compiled Lisp function insubr.el.
(backtrace)Print a trace of Lisp function calls currently active.
Output stream used is value of
standard-output.
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1This is almost there, but prints to stdout instead of stderr. Instead you need
(let ((standard-output 'external-debugging-output)) (backtrace))– wasamasa Apr 10 '20 at 7:19 -
@wasamasa: Yes, that info helps. (But the question does say, "into the stdout/stderr for example".) – Drew Apr 10 '20 at 16:54
(let ((debug-on-error t))
(error "test"))
With emacs -Q --batch -l tmp/test.el the following is printed to stderr:
Debugger entered--Lisp error: (error "test")
signal(error ("test"))
error("test")
(let ((debug-on-error t)) (error "test"))
eval-buffer(#<buffer *load*> nil "/home/wasa/tmp/test.el" nil t) ; Reading at buffer position 44
load-with-code-conversion("/home/wasa/tmp/test.el" "/home/wasa/tmp/test.el" nil t)
load("/home/wasa/tmp/test.el" nil t)
command-line-1(("-l" "tmp/test.el"))
command-line()
normal-top-level()
If there's a situation where it doesn't work, chances are errors are inhibited by the code in question.
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1Is there a way to do this that gets the stack trace but doesn't cause the code to halt? - e.g: gets the stack-trace as a string? – ideasman42 Apr 9 '20 at 12:18
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This doesn't work in all cases, eg: in a function registered via
jit-lock-register:Error during redisplay: (jit-lock-function 1501) signaled (error "test")– ideasman42 Apr 9 '20 at 12:22 -
Hence the "chances are errors are inhibited by the code in question", popping up a debugger during redisplay is not an option. – wasamasa Apr 10 '20 at 7:14
