[Interest] [Development] Qt 6.5 Is Irrelevant for More than 95% of Mac Desktops

[Thiago Macieira]

On Friday, 16 December 2022 18:15:11 -03 Alexander Dyagilev wrote:
> But why did you do this? Does the supporting of 10.15 really increase
> the development cost for Qt Company?

I can't speak for the Qt Company costs, particularly for the fact that this is 
one of their LTS releases.

But in general, it does increase the costs overall. There are new APIs that we 
can use if we don't have to keep 10.15 compat, there's one fewer platform to 
test on (usually with a virtual machine) before release, and so on. The 
benefits may not be realised now, but they will come in the future.

For me specifically, what matters is that 11.0 dropped support for Intel Macs 
that don't have AVX2 support, meaning that I can now assume that all machines 
running Qt 6.5 natively have it. We had further changes based on this 
assumption ready to go for 6.5, but they got removed at the last minute due to 
unexpected side-effects and the feature freeze being too close.

On Friday, 16 December 2022 19:44:16 -03 Michael Jackson wrote:
> I agree here. Is Qt 6.5 now using an API or a compiler feature that macOS
> 10.15 does not support? 

As of *today*, no. This may change tomorrow, as developers continue to do 
their work. That means that, as of *today*, Qt 6.5 *could* be compiled to run 
on 10.15, by just lowering the default minimum version somewhere in a config 
file. But we are not promising that this will remain true and especially we are 
not testing that it works.

We had to make a call and following Apple's own support lifetime makes sense. 
If you want to stay on an OS that is not receiving important fixes, then you 
can also stay on a Qt that is not receiving fixes. Though unlike Apple, you can 
backport fixes to 6.4 yourself or remove the new requirements from 6.5 yourself 
(or contract someone to do it for you).

Moreover, there's a time delay. This affects Qt 6.5, which will be released in 
March 2023, which means it probably affects applications released in May 2023 
and later.

>  Is there a security library that Qt 6 depends on (OpenSSL is my guess) that
>  10.15 isn't now updating? Is Qt 6 using the new APIs from that version of
>  OpenSSL (or what ever library broke)? Is there a graphics API that Qt 6
>  now depends on that is macOS 11.0 and greater? Maybe that is the reason?

Any of the above or others may become another reason. The point is that we 
need to officially drop the platform first, before we can depend on and require 
some of those APIs. It's not the other way around.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Cloud Software Architect - Intel DCAI Cloud Engineering