Criteria for picking compilers from fallback list ?

[Christopher Jones]

> On 7 Dec 2016, at 5:32 pm, Joshua Root <jmr at macports.org> wrote:
> 
> On 2016-12-8 04:24 , Chris Jones wrote:
>> Hi,
>> 
>> I'm working on an update to the root6 port, where the minimum compiler
>> requirement has been increased in the latest release, such that I need
>> to update the compiler blacklist/fallback to force a macports compiler
>> to be used on OSX 10.8 and 10.9 (whereas previously the system one was OK).
>> 
>> This is all working OK, but I have noticed one thing I am trying to
>> understand is on 10.8 and 10.9 different fallbacks are being picked.
>> 
>> I have
>> 
>> compiler.blacklist-append *gcc* {clang < 602} macports-clang-3.3
>> macports-clang-3.4 macports-clang-3.5 macports-clang-3.6
>> compiler.fallback-append macports-clang-3.9 macports-clang-3.8
>> macports-clang-3.7
>> 
>> On 10.8 this is causing macports clang 3.9 to be picked, whereas on 10.9
>> clang 3.8 is being used. I am curious as to what the logic is in the
>> blacklist portgroup that is leading to this different decisions to be
>> made ? I thought perhaps it was based on what clang ports where already
>> installed, but even after uninstalling all clang versions, the same
>> decisions are being made. Just curious...
> 
> The initial value of compiler.fallback differs based on cxx_stdlib because clang 3.5+ needs libc++. And yes, this will mean trouble for users on 10.8 who are using the default cxx_stdlib.

Ah, I didn’t consider the cxx_stdlib differences. Still not sure though how that exactly translates into different decisions w.r.t. clang 3.8 versus 3.9 though. Is it just the different list means a different (random) decision is taken ? both are >3.5 so on the same field regarding the stdlib used.

Chris

> 
> - Josh

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