Bold Small Caps in all sections, using lmodern default package

Question

I am writing a document using lmodern package and I need to redefine all sections in order to be bolded and in small caps. I cannot change the lmodern font for another one including bold small caps and tricks like

\usepackage{lmodern}
\usepackage{fontspec}
\usepackage[T1]{fontenc}

{\fontfamily{cmr}\textsc{\textbf{Hello World}}}

do not seem to work in Lualatex when I define:

\titleformat{\section}[hang]{\centering\fontfamily{cmr}\large\textsc\textbf}{\Roman{section}.}{2ex}{}[]

Is there a way to make all sections bolded and small caps while keeping lmodern package for the rest of the document?

Answer 1

The lmodern package isn't compatible with fontspec. And lmodern isn't really compatible with LuaLaTeX anyway.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\begin{document}

Straße

Wrocław

\end{document}

Compile with LuaLaTeX to get

However, if you remove lmodern and fontenc, you don't get boldface small caps, because this combination is not available in Latin Modern fonts.

\documentclass{article}

\begin{document}

Straße Wrocław

\textbf{\textsc{Abc}}

\end{document}

Now the first words are typeset as intended, but there's no boldface small caps.

You can use New Computer Modern instead, that's essentially indistinguishable from Latin Modern.

\documentclass{article}
\usepackage{fontsetup}
\usepackage{titlesec}

\titleformat{\section}[hang]
  {\filcenter\large\scshape\bfseries}
  {\Roman{section}.}
  {1em}
  {}

\begin{document}

\section{Straße Wrocław}

\textbf{\textsc{Abc}}

\end{document}

Answer 2

You don't need the lmodern package as Latin Modern is the default lualatex font. It doesn't have bold small caps, but you could define a font family for Computer Modern Unicode, and use that where you need smallcaps.

You should also never use \usepackage[T1]{fontenc} with lualatex.

\documentclass{article}
\usepackage{fontspec}
\newfontfamily\cmu{CMU Serif}

\makeatletter
\renewcommand\section{\@startsection {section}{1}{\z@}%
                                   {-3.5ex \@plus -1ex \@minus -.2ex}%
                                   {2.3ex \@plus.2ex}%
                                   {\normalfont\cmu\Large\bfseries\scshape}}
                                         %%%%%%                 %%%%%%%%%%x

\makeatother
\begin{document}

{\cmu \textsc{Abc Def} \textsc{\bfseries Abc Def}}

\section{Caps and Small Caps}
xxx

\end{document}