[MacPorts] #62711: Base: port rdeps --full, infinite loop on circular dependency

[MacPorts]

#62711: Base: port rdeps --full, infinite loop on circular dependency
--------------------------+--------------------
 Reporter:  Dave-Allured  |      Owner:  (none)
     Type:  defect        |     Status:  new
 Priority:  Normal        |  Milestone:
Component:  base          |    Version:  2.6.4
 Keywords:                |       Port:
--------------------------+--------------------
 This was first reported in port bug #62277 for **py-attrs** circular
 dependency.  This is the bug report for `rdeps` in the base, not the port.

 `port rdeps --full py-attrs` prints endlessly in infinite loop. \\
 `port rdeps py-attrs` prints normally and shows 37 dependencies.

 * Base version 2.6.4
 * py-attrs @20.3.0_0
 * py-hypothesis @6.8.4_0
 * Mac OS 10.14.5

 * py-attrs --> py-hypothesis --> py-attrs
 * py-attrs is a **normal library dependency** of py-hypothesis.
 * py-hypothesis is a **test dependency** of py-attrs.

 Requested base behavior:
 * Print warning message when circular dependency is first encountered.
 * Do not recurse into circular dependency.

-- 
Ticket URL: <https://trac.macports.org/ticket/62711>
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