The future of macos vs. macos_arm

[Makarius]

Since macOS 26 is the last version that supports the old Intel platform via 
emulation, we need to reconsider our traditional approach to the macOS 
platform, where the Isabelle distribution (and ".app") was "hybrid" for Intel 
and ARM. Thus the same download worked on both platforms, but on ARM it 
required Rosetta 2, which is going to disappear after macOS 26.

Concerning Intel, I have now invested 360 EUR into a refurbished Mac Mini 2018 
(i3 with 4 cores, 16 GB RAM, 1 TB SSD). The 2018 line is the last one using 
Intel CPUs, it supports macOS 12, 13, 14, 15, but not macOS 26. See also 
https://everymac.com/systems/apple/mac_mini/specs/mac-mini-core-i3-3.6-late-2018-specs.html 
for details.

Thus we can easily continue x86_64-darwin for Isabelle contrib executables, as 
long as we have macOS 12..15 as our active baseline. There are many years 
ahead, until the upper end macOS 15 will have to be discontinued. Only 
afterwards, our support for macOS will be for ARM exclusively. Note that I 
will soon discontinue macOS 12 and move to macOS 13, because it helps to 
provide uniform VSCodium and GHC/stack executables.

Concerning pure arm64-darwin support, there is still a lot of homework to do 
concerning external provers and solvers. When that is done, we can split the 
Isabelle application bundle into x86_64-darwin vs. arm64-darwin. That will 
mark the beginning of the "macos" vs. "macos_arm" era, following the "linux" 
vs. "linux_arm" from some years ago. (It will be many more years, until 
windows_arm might become relevant.)

I would like to see macos_arm already for Isabelle2026 (October 2026), but it 
is probably more realistic for a subsequent Isabelle release in 2027. Note 
that when macOS 27 hits the end-user market, people can no longer run Isabelle 
with all its add-on tools.


	Makarius