breaking font selection with LuaLaTeX and fontspec

[cabohah]

It seems, that polyglossia breaks fonts names with whitespaces when using LuaLaTeX and fontspec, e.g.:

\documentclass{report}
\usepackage{fontspec}
\usepackage{polyglossia}
\setmainfont[Ligatures=TeX]{TeX Gyre Termes}
\begin{document}
  \slshape
  This is a sentence.
\end{document}

results in:

luaotfload | db : Reload initiated (formats: otf,ttf,ttc); reason: Font "TeX" not found.
./test.tex:6: Font \TU/TeXGyreTermes(0)/m/it/10=name:TeX not loadable: metric data not found or bad.
<to be read again> 
G
l.6   \slshape

So it seems, that the font name is TeX.

A workaround would be to load polyglossia after \setmainfont or to use TeXGyreTermes (without spaces) as font name.

There error does not occur with XeLaTeX instead of LuaLaTeX.

See also https://tex.stackexchange.com/q/721772/277964.

I'm not absolutely sure, that this is a polyglossia issue, but because the error does not occur without polyglossia or when using babel instead of polyglossia, I report it here.

[cfr42]

It's an issue with the Harfbuzz renderer rather than polyglossia. You can reproduce without polyglossia:

\documentclass{book}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX,Renderer=Harfbuzz]{TeX Gyre Termes}

\begin{document}
\slshape 
This is a sentence.
\end{document}

[amunn]

The problem is caused by the fact that polyglossia uses the HarfBuzz renderer by default. So I'm not sure this is a polyglossia problem. It's really a fontspec problem:

\documentclass{book}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX,Renderer=HarfBuzz]{TeX Gyre Termes}

\begin{document}
This is a sentence.
\end{document}

[Udi-Fogiel]

You can change the default renderer with the luatexrenderer option of the package, FWIW.

[cfr42]

It is not really class dependent, I don't think. The difference between article and book is probably in what they do at \begin{document}.

\documentclass{article}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX,Renderer=Harfbuzz]{TeX Gyre Termes}

\begin{document}
\slshape 
This is a sentence.
\end{document}

also reproduces.

[cabohah]

It's also class dependent, because this example works for me with article or report class.

Not if you add, e.g., \slshape into an example using article or report.

[Udi-Fogiel]

This is a bug in luaotfload, I've reported it in latex3/luaotfload#285.

I'm closing this ticket, but feel free to reopen it if you think my analyze is wrong.