Bug#542767: apt: autoremove removes needed packages

[peter green <plugwash@p10link.net>]

> I tried to install Internet Explorer to view a web site designed for IE. 
> Downloaded IE8 from microsoft.com, installed wine, installed current 
> wine beta from winehq. Didn't work. Tried viewing the web site with 
> epiphany (already installed) and lynx. Installed and tried konqueror,
> galeon. Removed epiphany, galeon and konquerer in one apt-get call.
>
> Then a lot of packages were marked for autoremoval

This sounds like a case of what I call the "metapackage up/down problem"

The basic scenario goes as follows

* the user (or possiblly some software such as tasksel) installs a metapackage (in this case it appears it was "gnome").
* since the only package the user manually installed was the metapackage everything the metapackage depends on is considered automatically installed
* the user removes one or more packages that the metapackage depends on (in this case the epiphany packages) causing the metapackage to be removed
* with the metapackage gone the other stuff the metapackage pulled in is now considered "automatically installed and no longer required"

The problem with this issue is it's not bug in how the algorithm is implemented, it's working as designed. It's just that the design is producing surprising results (removing one desktop app can result in a metapackage being removed and the whole desktop being marked as "automatically installed an no longer required")

> be:~# apt-get purge epiphany-browser-data epiphany-extensions epiphany-extensions-more epiphany-gecko galeon konqueror                                                                
> Reading package lists... Done                                                     
> Building dependency tree                                                          
> Reading state information... Done  
> The following packages were automatically installed and are no longer required:  
<snip>
> The following extra packages will be installed:                                                   
>  gnome-core gnome-desktop-environment                                                            
> Suggested packages:                                                                               
>  gnome-dbg                                                                                       
> Recommended packages:                                                                             
>  gnome-accessibility                                                                             
> The following packages will be REMOVED:                                                           
>  epiphany-browser* epiphany-browser-data* epiphany-extensions* epiphany-extensions-more*         
>  epiphany-gecko* galeon* gnome* konqueror*                                                       
> The following packages will be upgraded:                                                          
>  gnome-core gnome-desktop-environment                                                            
> 2 upgraded, 0 newly installed, 8 to remove and 435 not upgraded.                                  
> Need to get 0B/31.0kB of archives.                                                                
> After this operation, 23.3MB disk space will be freed.                                            
> Do you want to continue [Y/n]?  
We can clearly see here that your removals triggered the removal of the "gnome" metapackage. This is almost certainly what triggered the large list of "automatically installed and no longer required packages"