[MacPorts] #65299: Guide 3.2.1: Say that variant specification on port install does not overrule existing ports

[MacPorts]

#65299: Guide 3.2.1: Say that variant specification on port install does not
overrule existing ports
-------------------------+--------------------
 Reporter:  JDLH         |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  guide        |    Version:  2.7.2
 Keywords:               |       Port:
-------------------------+--------------------
 The [https://guide.macports.org/#using.variants.invoking MacPorts Guide,
 section 3.2.1. Invoking Variants] does not describe well how `port
 install` propagates variant invocations to dependencies. It should explain
 a) how it propagates variant invocations to not-installed dependencies, b)
 how it does not overrule variants on installed dependencies, and c)
 mention of the `--enforce-dependencies` option.

 The Guide presently says, "This [MacPorts not warning about misspelled
 variant names] happens because MacPorts will also use the specified
 variants for any dependencies." That is an oblique reference to `port
 install` propagating variants. The explanation should be clearer, and
 include all three elements above.

 This behaviour is discussed in a [https://lists.macports.org/pipermail
 /macports-users/2022-June/051202.html MacPorts-user list thread "Should I
 expect a +quartz variant to propagate to dependencies, and overrule
 existing variants?"] from June 2022. It may have helpful information for a
 writer.

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Ticket URL: <https://trac.macports.org/ticket/65299>
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