[MacPorts] #60565: Make setting known_fail yes prevent installation of deps

[MacPorts]

#60565: Make setting known_fail yes prevent installation of deps
-------------------------+--------------------
 Reporter:  ryandesign   |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:  2.6.2
 Keywords:               |       Port:
-------------------------+--------------------
 Some ports do this (this is from gcc49):

 {{{
 if {${os.platform} eq "darwin" && ([vercmp $xcodeversion 9.0] > 0)} {
     known_fail      yes
     depends_lib
     depends_run
     archive_sites
     pre-fetch {
         ui_error "building ${name} is not supported with Xcode 9 or
 greater"
         return -code error {unsupported platform}
     }
 }
 }}}

 In other words in addition to setting `known_fail yes` and printing an
 error message, it clears the dependencies. I guess the intention of this
 is to avoid the annoying situation where a user asks to install a port,
 spends a lot of time installing its dependencies, and only then discovers
 that the port they wanted won't work on their system anyway. Maybe
 MacPorts base could arrange for the dependencies to be cleared
 automatically when `known_fail yes` is used.

 The disadvantage of this is that when a user runs `port info` or `port
 deps` they won't see the dependencies that would be required if the port
 worked, which is valuable and relevant information. The dependencies would
 also be absent from the portindex for that OS version, which could be bad
 since the MacPorts web app gets its information from the portindex for one
 particular OS version. Maybe there is a way for MacPorts base to keep the
 dependencies visible in `port info` and `port deps` and the portindex but
 to skip trying to install them.

 A [ticket:60564 separate ticket] tracks clearing `archive_sites`.

-- 
Ticket URL: <https://trac.macports.org/ticket/60565>
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