[luatex] Problem with babel-greek (harfbuzz?)

[Nikos Platis]

Στις Τρί 17 Οκτ 2023 στις 12:20 μ.μ., ο/η Ulrike Fischer <luatex at nililand.de>
έγραψε:

> Am Tue, 17 Oct 2023 09:51:55 +0300 schrieb Nikos Platis:
>
> > Dear all,
> >
> > I came across a rather strange issue while using lualatex with
> babel-greek.
> > I am posting here because I believe it is mostly related to lua(la)tex
> and
> > less to babel-greek.
> >
> > Here is an MWE:
> >
> > ----------------------------
> > % !TeX program = lualatex
> >
> > \documentclass{book}
> >
> > \usepackage[sf,bf]{titlesec}
> >
> > \usepackage[greek]{babel}
> > \babelfont[greek]{rm}{Times New Roman}
> > \babelfont[greek]{sf}{Arial}
> >
> > % \usepackage{polyglossia}
> > % \setmainlanguage{greek}
> > % \newfontfamily\greekfont[Script=Greek]{Times New Roman}
> > % \newfontfamily\greekfontsf[Script=Greek]{Arial}
> >
> > % \usepackage[no-math]{fontspec}
> > % \defaultfontfeatures{Ligatures=TeX}
> > % \setmainfont{Times New Roman}
> > % \setsansfont{Arial}
> > % \usepackage{xgreek}
> >
> > \begin{document}
> >
> > \tableofcontents
> >
> > \chapter{Πρώτο Κεφάλαιο}
> > Καλησπέρα \TeX. Πρώτο Κεφάλαιο.
> >
> > \end{document}
> > ----------------------------
> >
> > I was compiling this on fully updated Arch Linux with lualatex from
> texlive
> > (not Arch Linux packages). The result is the attached pdf file. You can
> see
> > the strange accents in "Περιεχόμενα" and "Κεφάλαιο". You can also see
> that,
> > for example, "Κεφάλαιο" appears correctly in the text.
> >
> > After a lot of testing, I found out that this happens only for lualatex
> > (not xelatex) with babel-greek (not polyglossia or xgreek) (only in the
> > "stock" strings, "Περιεχόμενα", "Κεφάλαιο") and lualatex from texlive
> (not
> > with lualatex from the Arch Linux package).
> >
> > [....]
> > The crucial difference is probably in harfbuzz. But how can this impact
> the
> > output in the ways described above?
>
> The harfbuzz version is not relevant.
>
> In the faulty words the ά is not U+03AC (alpha with tonos) but U+3B1
> (alpha) with a following U+0301 (combining acute accent) (and
> similar for the other char with accent).
>
> If the greek hyphenation patterns are used an discretionary is
> inserted between char and accent and that disturbs the placement:
>
> \documentclass{book}
>
> \usepackage{babel}
> \usepackage{fontspec}
> \setmainfont{Times New Roman}
> \setsansfont{Arial}
> \textwidth=1pt
> \begin{document}
> \selectlanguage{greek}
> \showoutput
>
> Κεφάλαιο
> Κεφάλαιο
>
> \sffamily
> Κεφάλαιο
> Κεφάλαιο
>
> \end{document}
>
> basically it means that the greek hyphenation patterns needs a
> correction, see https://tex.stackexchange.com/a/340164/2388 and
> https://tex.stackexchange.com/q/330180/2388 for a similar problem
> with russian.
>
> You can avoid the problem by using the harfbuzz renderer, e.g.
>     \babelfont[greek]{sf}[Renderer=harfbuzz]{Arial}
> It typically suppress some problematic hyphenation points as it
> builds clusters earlier. (polyglossia uses harfbuzz by default,
> that's why you don't see the problem there).
>
> Another option is to redefine \contentsname and \chaptername and to
> remove the accent introduced by babel-greek here:
>
> \addto\captionsgreek{\renewcommand\chaptername{Κεφάλαιο}%
> \renewcommand\contentsname{Περιεχόμενα}}
>
>
> The real fix is naturally to correct the hyphenation patterns.
>
>
>
> --
> Ulrike Fischer
> http://www.troubleshooting-tex.de/
>
>
Thank you for your prompt answer.
I remember that in the past I had witnessed similar problems when copying
texts from a Mac which, I think, uses combining accents.

I will write to the tex-hyphen list about it.

It is still puzzling, though, why the problem was not present earlier
(around June, for example, I was working with the same document that
triggered this report, without any issues) or it does not show using the
Arch Linux lualatex (which is packaging a texlive version around March).
Maybe something has changed with babel-greek in the meantime.
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