bug#58168: string-lessp glitches and inconsistencies

[Eli Zaretskii <eliz@gnu.org>]

> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Mon, 3 Oct 2022 21:48:10 +0200
> Cc: 58168@debbugs.gnu.org,
>  Eli Zaretskii <eliz@gnu.org>
> 
> 1 okt. 2022 kl. 15.51 skrev Eli Zaretskii <eliz@gnu.org>:
> 
> > I think the variable is a misnomer of sorts: the request back when it
> > was introduced to display hex where we usually display octal \nnn
> > escapes.  And the latter happens not only for raw bytes.
> 
> Fair enough. Maybe the documentation should reflect that, but I'm still holding out for a change to the C1 presentation in the long term, so...
> 
> I'm not going to pursue this little digression any further except that while looking at it I found a few inaccuracies and a likely bug in redisplay-testsuite.el. I'm attaching a patch which un-muddles the test and adds a display of unprintable Unicode chars such as C1 controls, in addition to raw bytes. I'd like to adorn the commit with the correct bug number so if you remember that of the original discussion that would be useful (I never found it very easy to search debbugs).

First I needed to fix fallout from making STRING_CHAR intolerant of
unibyte text, because redisplay-testsuite caused assertion violations
in string_char_and_length.  (Doesn't it abort for you? or do you not
build Emacs with --enable-checking?)  This was a regression in Emacs
28, sigh.

Looking at your patch, I don't think I understand this part:

> --- a/test/manual/redisplay-testsuite.el
> +++ b/test/manual/redisplay-testsuite.el
> @@ -305,7 +305,7 @@ test-redisplay-5-toggle
>    (let ((label (if display-raw-bytes-as-hex "\\x80" "\\200")))
>      (overlay-put test-redisplay-5a-expected-overlay 'display
>                   (propertize label 'face 'escape-glyph)))
> -  (let ((label (if display-raw-bytes-as-hex "\\x3fffc" "\\777774")))
> +  (let ((label (if display-raw-bytes-as-hex "\\xfc" "\\374")))
>      (overlay-put test-redisplay-5b-expected-overlay 'display
>                   (propertize label 'face 'escape-glyph))))
>  
> @@ -320,18 +320,36 @@ test-redisplay-5
>          (test-insert-overlay " " 'display "\200"))
>    (insert "\n\n")
>    (insert "  Expected: ")
> -  ;; This tests a large codepoint, to make sure the internal buffer we
> -  ;; use to produce the representation is large enough.
> -  (aset printable-chars #x3fffc nil)
>    (setq test-redisplay-5b-expected-overlay
>          (test-insert-overlay " " 'display
> -                             (propertize "\\777774" 'face 'escape-glyph)))
> +                             (propertize "\\374" 'face 'escape-glyph)))

I could understand why you'd want to _add_ the larger values, but why
replace?

As for the bug report which led to display-raw-bytes-as-hex (if that
what you meant) and its discussion, it's bug#27122.  (If you know what
code is in question, it is much easier to find the bug via "git
annotate", assuming the bug number was cited in the commit logs.)