bug#16762: Installed packages are not considered part of the archive contents

[Dmitry Gutov <dgutov@yandex.ru>]

On 22.03.2014 04:46, Stefan Monnier wrote:

> Yes, but as long as we don't know why this was done, it's too risky to
> change it.  If/when we figure out what that was about and come up with
> a way to fix the problem, we can judge whether that's appropriate for
> 24.4.

 From what I can see, except `package-install', all places where 
`package-archive-contents' is used, either append its contents to 
`package-alist' elements, or use a predicate calling `package-installed-p'.

The following patch seems to offer the same functionality:


=== modified file 'lisp/emacs-lisp/package.el'
--- lisp/emacs-lisp/package.el	2014-03-22 08:43:30 +0000
+++ lisp/emacs-lisp/package.el	2014-03-23 08:03:37 +0000
@@ -1047,14 +1047,11 @@
           (existing-packages (assq name package-archive-contents))
           (pinned-to-archive (assoc name package-pinned-packages)))
      (cond
-     ;; Skip entirely if pinned to another archive or already installed.
+     ;; Skip entirely if pinned to another archive or built-in.
       ((or (and pinned-to-archive
                 (not (equal (cdr pinned-to-archive) archive)))
            (let ((bi (assq name package--builtin-versions)))
-            (and bi (version-list-= version (cdr bi))))
-          (let ((ins (cdr (assq name package-alist))))
-            (and ins (version-list-= version
-                                     (package-desc-version (car ins))))))
+            (and bi (version-list-= version (cdr bi)))))
        nil)
       ((not existing-packages)
        (push (list name pkg-desc) package-archive-contents))
@@ -1090,8 +1087,11 @@
         (package-refresh-contents))
       (list (intern (completing-read
                      "Install package: "
-                    (mapcar (lambda (elt) (symbol-name (car elt)))
-                            package-archive-contents)
+                    (delq nil
+                          (mapcar (lambda (elt)
+                                    (unless (package-installed-p (car elt))
+                                      (symbol-name (car elt))))
+                                  package-archive-contents))
                      nil t)))))
    (package-download-transaction
     (if (package-desc-p pkg)