Small caps issue with Xelatex

Question

Problem

I've just bought Baskerville Classico font and tried to load it using Xelatex, but small caps didn't work. I finally found this post : [https://tex.stackexchange.com/questions/165998/small-caps-in-fontspec-on-xelatex]... added this piece of code and loaded it with LuaLaTex and it works:

    \setmainfont[
  SmallCapsFont={TeX Gyre Termes},
  SmallCapsFeatures={Letters=SmallCaps},
]{Baskerville Classico}

Is my preamble correct?

This is a MWE:

    \documentclass[hidelinks,12pt,twoside,openright,a4paper]{book}
    \usepackage[french]{babel}
    \usepackage{fontspec}
    \setmainfont[
  SmallCapsFont={TeX Gyre Termes},
  SmallCapsFeatures={Letters=SmallCaps},
]{Baskerville Classico}
    \usepackage{lipsum}
    \usepackage{fancyhdr}
    \pagestyle{fancy}
    \renewcommand{\chaptermark}[1]{\markboth{#1}{}}
    \renewcommand{\headrulewidth}{0pt}
    \fancyhf{} % sets both header and footer to nothing
    \fancyfoot{}
    \fancyhead[LE,RO]{\thepage}
    \fancyhead[CE]{\textsc{A title}} % even pages: chapter title
    \fancyhead[CO]{\textsc\leftmark} % odd pages: book title
    
    \begin{document}
    
    \chapter{A title}
    \lipsum
    
    \end{document}

Solution

Finally, I found the solution. This is the piece of code to add instead of Tex Gyre Termes:

\setmainfont[
  SmallCapsFont={BaskervilleClassicoSC},
  SmallCapsFeatures={Letters=SmallCaps},
]{Baskerville Classico}

Answer 1

I’ll migrate my advice, which the OP confirms was helpful, into an answer rather than the comments.

By default, fontspec tries to activate the feature it calls Letters=SmallCaps and OpenType calls smcp. You can check whether a given font has this feature with the command otfinfo -f, followed by the absolute filename with its path. You can get the filename from the display name of the font with luaotfload-tool --find. You typically want to put names that contain spaces in double quotes on the command line.

In this case, you told me that the filename was /Library/Fonts/Linotype - Baskerville Classico.otf, and that it did not have this feature. There was, however, another font face in the same directory that did have small caps, Linotype - Baskerville Classico SC.otf.

Typically, you would load a separate small-caps face like this by adding options like

\defaultfontfeatures[BaskervilleClassico]{
  % Set Ligatures, Numbers, etc.
  SmallCapsFont={* SC},
  SmallCapsFeatures={} }

\setmainfont{BaskervilleClassico}

If there’s also a bold or italic small caps face, you would load that with options like, hypothetically,

  ItalicFeatures = { SmallCapsFont = {*-SC-Italic},
                     SmallCapsFeatures = {} },

What methods of loading a file vary between XeTeX and LuaTeX on different OSes, but using the exact filename with Extension= is usually recommended.

Here, what seemed to work was the family name and style. You can get a list of the possible family and style names that fontspec might understand with otfinfo -i, and test whether LuaTeX can look up a name with luaotfload-tool --find or whether XeTeX can look it up with fc-match.