PREFIXDIR/share/emacs/28.2/site-lisp/subdirs.el (or something like
d:/Progs/emacs-28.2/share/emacs/28.2/site-lisp/subdirs.el on MS-Windows):
(if (fboundp 'normal-top-level-add-subdirs-to-load-path)
However, according to Summary: Sequence of Actions at Startup:
When Emacs is started up, it performs the following operations:
- It adds subdirectories to
load-path, by running the file named
subdirs.elin each directory in the list. Normally, this file adds the directory’s subdirectories to the list, and those are scanned in their turn. The files
subdirs.elare normally generated automatically when Emacs is installed.
it seems that whether
normal-top-level-add-subdirs-to-load-path is defined is an established fact that doesn't require runtime detection -- whether this function is defined when Emacs loads
site-lisp/subdirs.el is predictable.
normal-top-level-add-subdirs-to-load-path is somehow undefined, all subdirectories in
site-lisp make no sense, same as
I wonder why we need to use a runtime test here.