[GSoC] migration

[Joshua Root]

On 2017-7-27 14:57 , Joshua Root wrote:
> The order to follow when uninstalling is the reverse of the order used 
> when installing, i.e. dependents-first rather than dependencies-first. 
> Order does matter because we check whether a port has dependents when 
> uninstalling and raise an error if so. You can set a flag to ignore this 
> check, but warnings will still be printed, so it's better just to do it 
> in the right order.
> 
> Technically the structure of the dependency relationships of a set of 
> ports is a directed acyclic graph, not a tree. A DAG can be 
> topologically sorted, which is a bit like flattening a tree. When you're 
> dealing with a set of ports that don't all necessarily have dependencies 
> in common, only a partial ordering can be established, and that's what 
> you see in the sorting done by portlist_sortdependents in port.tcl (each 
> port comes earlier in the list than all its dependencies) and sort_ports 
> in restore_ports.tcl (each port is later in the list than all its 
> dependencies).

Oh and if you want a visualisation of the structure, have a look at 
port-depgraph. 
<https://github.com/macports/macports-contrib/blob/master/port-depgraph/port-depgraph>

- Josh