bug#50406: fill-paragraph error

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> Please try to open the attached file in emacs -Q, and after moving point
> to the beginning of the 3rd line, type 'M-q'.  When debug-on-error is t,
> it fails with such backtrace:
>
> Debugger entered--Lisp error: (error "Invalid search bound (wrong side
> of point)")
>   re-search-backward("[ \11]\\|\\c|.\\|.\\c|" 280 0)
>   fill-move-to-break-point(280)
>   fill-region-as-paragraph(184 210 nil nil 186)
>   fill-comment-paragraph(nil)
>   fill-paragraph(nil t)
>   funcall-interactively(fill-paragraph nil t)
>   command-execute(fill-paragraph)

This doesn't happen now in Emacs 29.  Instead I get:

abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc 
abc abc abc ; def
                                                                                
            ; def
                                                                                
            ; def
                                                                                
            ; def
                                                                                
            ; def
                                                                                
            ; ghi

Is that the result we're supposed to get, though?  I'm not at all sure
how fill-paragraph/comment-start are supposed to interact here.