bug#61069: 30.0.50; comint-copy-old-input should include continuation lines

[Eli Zaretskii <eliz@gnu.org>]

> From: Bob Rogers <rogers@rgrjr.com>
> Date: Wed, 25 Jan 2023 17:43:02 -0800
> 
>    In a shell-mode buffer with lots of "make" output, there will often
> appear commands with continuation lines.  To use them as new input
> (e.g. while debugging some bit of makefile logic) requires either
> marking and copying multiple lines, or multiple invocations of
> comint-copy-old-input (C-RET in shell-mode) to get the complete command.
> The attached patch against f0971f94fe42224b4d85bb8b6188d5d805689ddf in
> master includes those continuation lines, which seems like a desirable
> bit of dwimmery.  However, I may have misunderstood the purpose of the
> line-end-position vs. field-end thing.  Also, this assumes shell syntax,
> so it may be more appropriate to leave comint-get-old-input-default
> alone and give shell-mode its own shell-get-old-input-default function.

I don't understand: line-end-position already reports the entire line,
including continuation lines.  So could you explain the problem with
the current code in more detail, please?

> +               ;; Include continuation lines as long as the current
> +               ;; line ends with a backslash.
> +               (while (and (not (eobp))
> +                           (= (char-before) ?\\))
> +                 (goto-char (line-end-position 2))))

Or maybe I don't understand what is this "backslash" business is
about?  AFAICT, the "backslashes" shown for long lines of Make output
are those produced by the Emacs display, not by the shell, so the code
you want to change should already take care of that.

What am I missing?  Could you please show an example of "long Make
output" where the current code doesn't DTRT, so we'd be on the same
page wrt the problem?

Thanks.