bug#81539: 29.3; text-property-search-backward skips a matching region

Version: 31.1

Scott Guest [02/Aug  9:20pm -07] wrote:
> `text-property-search-backward' can skip a matching property region when it
> is followed by a one-character non-matching region.
>
> Run this command:
>
>   emacs -Q --batch --eval "(progn (require 'text-property-search)
> (with-temp-buffer (insert \"zxx-y\") (put-text-property 1 2 'p 'z)
> (put-text-property 2 4 'p 'x) (put-text-property 5 6 'p 'y) (goto-char
> (point-min)) (message \"forward:  %S\" (text-property-search-forward
> 'p 'x t)) (goto-char (point-max)) (message \"backward: %S\"
> (text-property-search-backward 'p 'x t))))"
>
> The output is:
>
>   forward:  #s(prop-match 2 4 x)
>   backward: nil
>
> The backward result should also describe [2,4).  Predicate t means that the
> property value must be `equal' to x, and both characters in [2,4) have that
> value.  The region is wholly before point, which is at point-max.
>
> The skip occurs in the non-matching branch of
> `text-property-search-backward'.  After it examines position 4,
> `previous-single-property-change' returns 2, but point remains at 4.  The
> next loop iteration repeats the call from position 4 and then examines
> position 1, skipping [2,4).
>
> This is distinct from Bug#58937: the matching region here is two characters
> wide; it is the following non-matching region that is one character wide.
>
> Reproduced in Emacs 29.3 and in Emacs 32.0.50 master at
> 1095d63d28fcdfd64a723efaaa4b965e5d846159.

Thanks, should be fixed on the emacs-31 branch.

-- 
Sean Whitton