TL/DR: Goldmark’s “typographer” extension isn’t an adequate replacement for smartypants, and Blackfriday now generates incorrect and potentially format-breaking HTML.
Taking them in turn, Goldmark now handles smartening apostrophes correctly, but still fails to correctly smarten double-quotes:
"This will be smart-quoted correctly!" ("this will not!") <i>"This won't be, either!"</i>
The results under 0.64 are:
<p>“This will be smart-quoted correctly!”</p> <p>(“this will not!")</p> <p><i>"This won’t be, either!“</i></p>
(the last example does not depend on the setting of Goldmark’s
Blackfriday handles all three correctly, but unfortunately, no longer escapes “<” in code blocks at all.
Since only Goldmark generates valid HTML under 0.64, I’d have to turn off the “typographer” extension and manually add smart-quoting to 3,000+ blog entries, and then remember to do it for all new blog entries. Or stick with 0.59.1, where it all works correctly.