Is it possible to dump all the default settings to a file?

As in you start Emacs where you have not added or changed any configuration and proceed to dump all the default settings to a file. TIA.

Considering not all files are even loaded when you `emacs -Q` that seems impossible. I suppose you could grep for all `defcustom` in the Lisp source

Ah I never considered that. Thanks for pointing that out.

https://www.gnu.org/software/emacs/manual/html_node/elisp/Watching-Variables.html

Download the Emacs source code (or clone the git repository), then build Emacs in the usual way. Now look in lisp/loaddefs.el. This file contains a record of every single function and variable defined in every single lisp file which is part of Emacs. It’s used by Emacs so that it doesn’t need to load every single lisp file at startup, because that would be slow. Instead it loads files whenever you call functions in them. There is also a generated file that contains information about functions and variables declared in the C code, though I am drawing a blank on the name. This one is in a different format, because it is only used by the help system; none of these need to trigger autoloads.

That's going to be a very big file. Not what you asked for, but if you're trying to review user-settings to see what there is, you could just "M-x customize RET" and then browse the groups.

Great, I'll try and give that a go.

Yes, I suspect you are right and it will be very big.