Xelatex, Minion Pro and Italian apostrophe kerning

Question

I know there are plenty of questions about it but after way too much searching I couldn't find a working fix. Some only work with lualatex, some with \usepackage{MinionPro}, some don't even compile...

Is there a way to fix the ugly apostrophe kerning with Minion Pro and xelatex? It's way too tight and completely wrong for Italian typographic styles. Minion is used extensively, I'm pretty sure I've seen it in several latex-produced-looking Italian documents, so there must be a solution. I'm about to abandon it and go back to the trustworthy Computer Modern where I didn't have to deal with this stuff.

Here's a mwe with an apostrophe rich paragraph, compile it with xelatex.

\documentclass[12pt]{article}
\usepackage{fontspec}
\usepackage{polyglossia}
\setmainlanguage{italian}
\usepackage{csquotes}
\defaultfontfeatures{Ligatures=TeX}
\setmainfont{Minion Pro}

\begin{document}
C'era un'oca con l'ala sinistra fratturata. L'altra ala era anch'essa
malmessa dopo l'estrema fatica del viaggio
d'oltreoceano. Per un po' poteva resistere ma un'operazione era
senz'altro consigliata.
\end{document}

and the same with Computer Modern

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[italian]{babel}
\usepackage[babel]{csquotes}

\begin{document}
C'era un'oca con l'ala sinistra fratturata. L'altra ala era anch'essa
malmessa dopo l'estrema fatica del viaggio
d'oltreoceano. Per un po' poteva resistere ma un'operazione era
senz'altro consigliata.
\end{document}

And the results, xelatex + Minion (see e.g. n'o which has no spacing at all)

and, much better, pdflatex + CM

Answer 1

It is actually not that hacky. Try the following (to be typeset with XeLaTeX):

\documentclass{minimal}

\usepackage{fontspec}

\setmainfont[Ligatures=TeX]{Minion Pro}

\makeatletter
\XeTeXinterchartokenstate=1

\newXeTeXintercharclass\LetterClass
\@tempcnta=`\A
\loop\unless\ifnum\@tempcnta>`\Z
  \XeTeXcharclass \@tempcnta \LetterClass
  \advance \@tempcnta by 1
\repeat
\@tempcnta=`\a
\loop\unless\ifnum\@tempcnta>`\z
  \XeTeXcharclass \@tempcnta \LetterClass
  \advance \@tempcnta by 1
\repeat

\newXeTeXintercharclass\ApostropheClass 
\XeTeXcharclass `’ \ApostropheClass
\XeTeXcharclass `' \ApostropheClass
\XeTeXinterchartoks \LetterClass \ApostropheClass = {\kern.1ex }
\XeTeXinterchartoks \ApostropheClass \LetterClass = {\kern.1ex }

\makeatother

\begin{document}

\begingroup\XeTeXinterchartokenstate=0 % Typeset without manual kerning
C'era un'oca con l'ala sinistra fratturata. L'altra ala era anch'essa
malmessa dopo l'estrema fatica del viaggio
d'oltreoceano. Per un po' poteva resistere ma un'operazione era
senz'altro consigliata.
\endgroup

C'era un'oca con l'ala sinistra fratturata. L'altra ala era anch'essa
malmessa dopo l'estrema fatica del viaggio
d'oltreoceano. Per un po' poteva resistere ma un'operazione era
senz'altro consigliata.

\end{document}

Minion Pro is known for its very small apostrophe kerning. LaTeX of course allows for manual kerning, but you want to kern certain glyph pairs every time they show up. Furthermore, you want to kern pairs like [every letter] [apostrophe].

So, we have to tell LaTeX what [every letter] shall be. This is done by assigning every letter from a to z and from A to Z to a certain charclass. An apostrophe is assigned to another charclass. Then, we tell LaTeX to add some kerning between these two classes.

The above code actually puts exactly this. As far as I know, you can only tell fontspec to generally increase or decrease kerning, but not for certain glyphs. If I read the other answers to similar problems on this platform, it seems to me that this is the most straightforward solution. Maybe someone else can provide a simpler one.