OK, I understand now; eval-when-compile works. The key was the part about "sometimes things get byte-compiled internally".

I think I see the problem; after-load-alist contains compiled functions. If I manually add to this list instead of using eval-after-load or use-package which does the same, then it works. Since the struct definition is not yet loaded when the function is compiled, setf can't possibly expand correctly. So the eval I added as a workaround really is necessary.

It's defined in lsp-mode.el, the file that I linked to. And I'm loading it with (require 'lsp-mode).

I tried requiring cl-lib before. I tried it again at the top-level as you suggested. I'm not compiling my init file. I tried compiling it once just to see and it didn't make any difference.

I put the entire function definition in an eval as a workaround. I'm going to leave this open as I still have no idea what the problem is.

I've restarted emacs a few dozen times while studying this. It's the same behavior every time. I also tried using with-eval-after-load instead of use-package. Still it's the same.

I had to use '/-:192.168.2.6|sudo::'. It's refusing to write the customizations. Setting 'tramp-default-proxies-alist' temporarily since "emacs -q" would overwrite customizations. I tried renaming my init.el, but I still get the same message.

I'm using ssh. I think I tried scp initially and it wasn't working, probably for the reason you just mentioned.

I get "Wrong type argument: listp, quote" with face-remap-set-base. Is there a way to do what I want to do?