* lisp/emacs-lisp/package.el (package-compute-transaction): Topological sort.

Add optional `seen' argument to detect and break infinite loops.

Fixes: debbugs:16994

lisp/ChangeLog

+2014-05-06  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* emacs-lisp/package.el (package-compute-transaction): Topological sort.
+	Add optional `seen' argument to detect and break infinite loops.
+
 2014-05-06  Eli Zaretskii  <eliz@gnu.org>
 	* emacs-lisp/find-gc.el (find-gc-unsafe, find-unsafe-funcs)
@@ -6,11 +11,11 @@
 2014-05-06  Michael Albinus  <michael.albinus@gmx.de>
-	* net/tramp-sh.el (tramp-remote-process-environment): Remove
-	HISTFILE and HISTSIZE; it's too late to set them here.  Add
-	:version entry.
-	(tramp-open-shell): Do not let-bind `tramp-end-of-output'.  Add
-	"HISTSIZE=/dev/null" to the shell's env arguments.  Do not send
+	* net/tramp-sh.el (tramp-remote-process-environment):
+	Remove HISTFILE and HISTSIZE; it's too late to set them here.
+	Add :version entry.
+	(tramp-open-shell): Do not let-bind `tramp-end-of-output'.
+	Add "HISTSIZE=/dev/null" to the shell's env arguments.  Do not send
 	extra "PSx=..." commands.
 	(tramp-maybe-open-connection): Setenv HISTFILE to /dev/null.
 	(Bug#17295)
@@ -126,8 +131,8 @@
 	(todo-edit-done-item--param-key-alist): New defconsts.
 	(todo-edit-item--prompt): New variable.
 	(todo-edit-item--next-key): New function.
-	(todo-key-bindings-t): Bind "e" to todo-edit-item.  Remove
-	bindings of deleted commands.
+	(todo-key-bindings-t): Bind "e" to todo-edit-item.
+	Remove bindings of deleted commands.
 2014-05-02  Leo Liu  <sdl.web@gmail.com>

lisp/emacs-lisp/package.el

@@ -868,7 +868,7 @@ MIN-VERSION should be a version list."
    ;; Also check built-in packages.
    (package-built-in-p package min-version)))
 
-(defun package-compute-transaction (packages requirements)
+(defun package-compute-transaction (packages requirements &optional seen)
   "Return a list of packages to be installed, including PACKAGES.
 PACKAGES should be a list of `package-desc'.
 
@@ -880,7 +880,9 @@ version of that package.
 This function recursively computes the requirements of the
 packages in REQUIREMENTS, and returns a list of all the packages
 that must be installed.  Packages that are already installed are
-not included in this list."
+not included in this list.
+
+SEEN is used internally to detect infinite recursion."
   ;; FIXME: We really should use backtracking to explore the whole
   ;; search space (e.g. if foo require bar-1.3, and bar-1.4 requires toto-1.1
   ;; whereas bar-1.3 requires toto-1.0 and the user has put a hold on toto-1.0:
@@ -893,15 +895,22 @@ not included in this list."
       (dolist (pkg packages)
         (if (eq next-pkg (package-desc-name pkg))
             (setq already pkg)))
-      (cond
-       (already
+      (when already
         (if (version-list-<= next-version (package-desc-version already))
-            ;; Move to front, so it gets installed early enough (bug#14082).
-            (setq packages (cons already (delq already packages)))
+            ;; `next-pkg' is already in `packages', but its position there
+            ;; means it might be installed too late: remove it from there, so
+            ;; we re-add it (along with its dependencies) at an earlier place
+            ;; below (bug#16994).
+            (if (memq already seen)     ;Avoid inf-loop on dependency cycles.
+                (message "Dependency cycle going through %S"
+                         (package-desc-full-name already))
+              (setq packages (delq already packages))
+              (setq already nil))
           (error "Need package `%s-%s', but only %s is being installed"
                  next-pkg (package-version-join next-version)
                  (package-version-join (package-desc-version already)))))
-
+      (cond
+       (already nil)
        ((package-installed-p next-pkg next-version) nil)
 
        (t
@@ -933,12 +942,13 @@ but version %s required"
                (t (setq found pkg-desc)))))
 	  (unless found
             (if problem
-                (error problem)
+                (error "%s" problem)
               (error "Package `%s-%s' is unavailable"
                      next-pkg (package-version-join next-version))))
 	  (setq packages
 		(package-compute-transaction (cons found packages)
-					     (package-desc-reqs found))))))))
+					     (package-desc-reqs found)
+                                             (cons found seen))))))))
   packages)
 
 (defun package-read-from-string (str)