This has been bothering me for a while when writing lisp code --
started happening roughly a few months ago.
Yup.
I always hit C-j for newline, and a couple of months ago, this
stopped indenting -- by default C-j runs control j runs the
command electric-indent-just-newline when electric-indent-mode
is on.
The documentation for electric-mode indicates that indentation
will be invoked when you type any of the chars in
electric-indent-chars -- and that variable is set to a list
containing ?\n which is ascii 10; yet, C-j invokes a command
that explicitly only inserts a newline? (feeling very confused)
It is not yet reflected in NEWS or the manuals, but `C-j' and
`RET' have been effectively swapped: `RET' now indents and `C-j'
does not indent.
The new behavior was apparently adopted to make Emacs correspond
better with what newbie users expect, based on their experience
with other editors and IDEs.
You are not alone in "feeling very confused". Hopefully, the
NEWS entry covering this, and perhaps the manuals, will explain
the best and simplest way to restore the previous, longstanding
behavior for those who might prefer it. Otherwise, you can
just retrain your fingers. ;-)