[MacPorts] #56730: port reclaim fails with circular dependencies

[MacPorts]

#56730: port reclaim fails with circular dependencies
---------------------------------+--------------------
 Reporter:  MarcusCalhoun-Lopez  |      Owner:  (none)
     Type:  defect               |     Status:  new
 Priority:  Normal               |  Milestone:
Component:  base                 |    Version:
 Keywords:                       |       Port:
---------------------------------+--------------------
 Recently, `port reclaim` added the ability [https://github.com/macports
 /macports-base/pull/20 to removed unrequested port].\\
 The procedure loops over every port and decides if it **or one of its
 dependents** is requested.\\
 To facilitate this procedure, the ports are put in
 [https://github.com/macports/macports-
 base/blob/a9579836b7b31158c1b3a67c4c5a7d9ffdbf572f/src/macports1.0/reclaim.tcl#L516
 sorted order].\\
 This works fine if [https://github.com/macports/macports-
 base/blob/a9579836b7b31158c1b3a67c4c5a7d9ffdbf572f/src/macports1.0/reclaim.tcl#L399
 the procedure] `sort_portlist_by_dependendents` works as advertised.\\
 If there is a circular dependency, then this is not possible.

 Some circular dependencies are requested by the user.\\
 For example:
 * install `librsvg`
 * install `adwaita-icon-theme` (depends on `librsvg`)
 * install `librsvg +viewer` (depends on `adwaita-icon-theme`)
 This results in `Error: reclaim failed: can't read "isrequested(librsvg)":
 no such element in array`.

 This issue was recently discussed on the
 [https://lists.macports.org/pipermail/macports-users/2018-June/045272.html
 mailing list].

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Ticket URL: <https://trac.macports.org/ticket/56730>
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