What does package-initialize do with package archives?

Question

I'm reading through the definition of package-initialize to try and understand what goes on under the hood, and part of what it does is to read the package archive files. I see it comparing version numbers, but I don't fully understand what it's doing at a high level.

I'm looking at this method:

(defun package-read-archive-contents (archive)
  "Re-read archive contents for ARCHIVE.
If successful, set the variable `package-archive-contents'.
If the archive version is too new, signal an error."
  ;; Version 1 of 'archive-contents' is identical to our internal
  ;; representation.
  (let* ((contents-file (format "archives/%s/archive-contents" archive))
     (contents (package--read-archive-file contents-file)))
    (when contents
      (dolist (package contents)
    (package--add-to-archive-contents package archive)))))

I think it's being used to make sure that the packages we're loading also have their descriptors added to the package archives (e.g. .emacs.d/elpa/melpa-stable/archive-contents if they're not already in there. But I'm not clear on what these archive-contents files are used for, since running a command like package-list-packages communicates with the remote package archive.

I apologize if this question is a bit muddled, but I'm trying to push through the awkward early stage of learning emacs.

I should also probably mention that the reason I started investigating the internals of package-initialize was to figure out if there's some kind of lazy-loading that I could be doing, rather than loading everything as soon as emacs starts up.

Answer 1

package-initialize is supposed to find all the installed packages and activate them (depending on the optional argument) by executing their <pkg>-autoloads.el files. Part of the complexity comes from the fact that it tries to make sure that it only activates a single version (the latest) of a given package (in case several versions of a package are installed).