Running dialyzer on both localhost and GitHub CI gives the following error:
:dialyzer.run error: The PLT file priv/plts/core.plt/dialyxir_erlang-24.3.4.17.plt is not writable
I solved it by creating the file priv/plts/core.plt/.keep in the repo. (If done after the .gitignore lines are added, it may have to be forced.)
@bjnord thanks for the comment and sorry you had an error.
One of the main concepts we wanted to shine through in the book is environment integrity, which means using the same versions of tools/infrastructure in all environments. When we wrote the book, we did so using version 26.2.1 of Erlang (which is the version of Erlang included in chapter 1) and it looks like you’re using version 24.3.4. So unfortunately, if you don’t use the same versions as we did when constructing the book then we can’t guarantee that your outcome will be the same as ours. Could you try using version 26.2.1 of Erlang (and 1.16.0 of Elixir) and see if this still happens? (Hopefully it shouldn’t).
Thanks @elliefairholm ! Yes, my devel box was too old to support 26 (a problem with openssl IIRC) so I dropped to 24. But it gave me the motivation to get this box upgraded. 
I will retry and I’m sure that will fix it.
I totally support that philosophy of the reader using exactly the same versions that you did when you wrote the book. So this one’s on me for sure.
And thank you for this book! I know a little bit about some of these technologies, but I am really deepening my knowledge and filling in some holes… learning a lot. Well done.
All the best!
Thank
Thanks for sharing your experience! I’m glad to hear you’re getting your box upgraded—it’s always nice when technical hiccups give us that extra push to improve our setups. I’m sure once you’re on the right version, things will go smoothly, keep us posted!
And thank you so much for your kind words about the book! It’s great to know that it’s helping you deepen your knowledge and fill in those gaps. That’s exactly what we were hoping for when we wrote it. 