bug#51037: [PATCH] Make `print-level` & `print-length` customizable in ERT batch tests

[Andy Moreton <andrewjmoreton@gmail.com>]

On Fri 08 Oct 2021, Lars Ingebrigtsen wrote:

> Andy Moreton <andrewjmoreton@gmail.com> writes:
>
>> Isn't that what ert-batch-backtrace-right-margin is for ?
>>
>>   (defcustom ert-batch-backtrace-right-margin 70
>>     "Maximum length of lines in ERT backtraces in batch mode.
>>   Use nil for no limit (caution: backtrace lines can be very long)."
>>     :type '(choice (const :tag "No truncation" nil) integer))
>>
>> Also the TEST_BACKTRACE_LINE_LENGTH environment variable can be
>> used to set it (see test/Makefile.in).
>
> Right.  But ert will still shorten "internally" with print-length etc
> before chopping the lines to 70 characters.  Here's with a longer value:
>
> est test-ensure-list2 backtrace:
>   signal(error ("(\"foo\" \"foo\" \"foo\" \"foo\" \"foo\" \"foo\" \"foo\" \"foo\" \"..."))
>   error("%S" ("foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo"
> "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo"
> "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo"
> "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo" "foo"
> "foo" ...))
>   (closure (t) nil (error "%S" (make-list 100 "foo")))()
>
> Note the "..." at the end of the foo list -- that's from print-length.


Good point. The truncation would not be so bothersome if there were
separate console and logfile streams (with the truncation only happening
in the console stream, and the full details in the logfile stream).

Anything that can make failed tests easier to diagnose is a useful
improvement.

    AndyM