Re: XCode 11.1 + Mac OS X 10.14.6 + pkgsrc 2019Q3

[Greg Troxel <gdt%lexort.com@localhost>]

"J. Lewis Muir" <jlmuir%imca-cat.org@localhost> writes:

> On 10/11, Edgar Fuß wrote:
>> EF> You need to download the SDK for the older macOS version.
>> EF> The downloads are somewhat hidden, but I explained how to find them.
>> 
>> LM> I don't understand how this works.  On macOS Mojave 10.14.5, Xcode 11.1
>> LM> appears to come with one macOS SDK, namely 10.15:
>>
>> Depends on what you mean by "how this works".
>
> I meant how I could select a deployment target of 10.6 and seemingly
> build an app for it just fine in Xcode yet only have the latest 10.15
> SDK.  Is it using weak linking?  Will it not tell me if I use something
> from a newer SDK (i.e., 10.7 to 10.15, in this case)?  If it doesn't
> tell me, then it will just fail at runtime which isn't helpful.  Is that
> why I actually need the SDK that corresponds to the deployment target so
> that I can actually tell when I'm trying to use something not available
> in the deployment target?

I think there is a lot of confusion about these SDKs :-)

My impression, perhaps off, is that there is

  XCode version X which tries to provide support for OS version Y, and
  might default to Y

  with an installed XCode, there are actually multiple sets of
  headers/libs that can target a number of OS versions

It sounds like you have an XCode which supports 10.15, but have it
configured to build programs targetted at 10.6.  Presumably macos has
binary compat so those programs run on newer systems.

Building for 10.15 and running on 10.13 or 10.14 is unsound and my
experience (with different versions, but going backward) is that some
things worked and some things failed.  Basically, the answer is "don't
do that" and ensure that the target OS is <= the OS you want to use it
on.

The question perhaps is really "Should XCode be thought of as containing
a set of SDKs, for different macos versions?"