问题
I have installed some packages by using elpa in my Emacs, but how are they loaded when launching Emacs?
回答1:
package-install is a part of package.el -- which You can see with describe-function. From package.el documentation:
;; At activation time we will set up the load-path and the info path,
;; and we will load the package's autoloads. If a package's
;; dependencies are not available, we will not activate that package.
So in every package there's a file
NAME-autoloads.el
and this file is loaded at start up.
The whole package is contained under the package-user-dir:
(setq package-user-dir "~/.emacs.d/site-lisp/package-install")
(require 'package)
Each package also contains NAME-pkg.el with package version and description. For example here're files related to tabbar package:
package-install # that's my package-user-dir
└── tabbar-2.0.1 # each package dir is in the separate dir
├── tabbar-autoloads.el # this file is loaded at start up
├── tabbar.el # the package itself. In this case it is just a single file
└── tabbar-pkg.el # information about the package for package managment
To quote the manual: 39.1.1 Summary: Sequence of Actions at Startup:
15. If package-enable-at-startup is non-nil, it calls the function package-initialize to activate any optional Emacs Lisp package that has been installed.
package-initialize is then calls package-activate which in turn calls package-activate-1 which ends with loading NAME-autoload.el:
(load (expand-file-name (concat name "-autoloads") pkg-dir) nil t)
来源：https://stackoverflow.com/questions/23306091/how-are-the-packages-installed-with-package-installelpa-in-emacs-loaded