[MacPorts] #55471: Use separate portindexes for libc++ on older systems

[MacPorts]

#55471: Use separate portindexes for libc++ on older systems
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  Reporter:  ryandesign   |      Owner:  neverpanic
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:  MacPorts 2.5.0
 Component:  base         |    Version:
Resolution:               |   Keywords:
      Port:               |
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Comment (by raimue):

 As Mojca [https://github.com/macports/macports-
 base/pull/83#issuecomment-383409609 asked] why I did not want to commit
 the changes to `macports.tcl`, let me explain that here.

 In the proposed changes to `macports.tcl`, `${platindex_cxxlib}` will be
 added to the remote PortIndex filename. It will only do this if the value
 of `cxx_stdlib` does not match the default.

 Side note: I do not understand why you would want to hardcode the default
 cxx_stdlib at this place. I would just always add `${platindex_cxxlib}` to
 the remote filename, isn't this much simpler? Wasn't your plan to
 eventually change the default on older systems at some point? Hardcoding
 default values seems to work against that.

 I also have reservations because of users that already have a non-default
 setting for `cxx_stdlib`. With this change, mportsync would expect a
 remote filename that does not yet exist. What are the consequences of
 this? Is the plan to deploy the changes to mprsyncup immediately after the
 2.5.0 release without ever testing the changes against rsync? Will
 mportsync fail gracefully or hard without a remote PortIndex file? Will
 base fall back to generate a PortIndex locally in this case? I see no
 reports of tests or consideration of it in this ticket.

 The changes to `macports.tcl` require the changes to `mprsyncup`, but that
 requires the changes to `portindex`.

 I can only review the change to portindex as ready-to-go. The new
 portindex would already fix the problem that PortIndex was generated with
 the wrong value of cxx_stdlib in mprsyncup for legacy platforms. This
 seemed to be the most important fix of this pull request to go into a
 release. I also thought this is what we discussed to do for MacPorts 2.5.0
 in our online meeting.

-- 
Ticket URL: <https://trac.macports.org/ticket/55471#comment:26>
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