[isabelle-dev] PLATFORMS: Mac OS X

Makarius makarius at sketis.net
Wed Apr 5 16:56:16 CEST 2017

On 05/04/17 12:48, Salomon Sickert wrote:
> Looking through the list of supported platforms I was wondering, how the
> deprecation cycle works.
> Wouldn’t it be a good idea to drop support for a platform if the vendor
> stops supporting it?

The aim is to make Isabelle "just work" on almost all platforms that
users happen to have around -- within reason. Empirically this means
that we need to go back in time by at least 5-7 years. Apart from that
there are platform-dependent side-conditions, when it becomes
unreasonable to support certain old systems.

Windows XP dropped out of the line recently, because Cygwin stopped
supporting it and moved the baseline up to Windows Vista or 7. Otherwise
I would have left XP in our porfolio: it is still the most popular
Windows version of all times, and I occasionally meet people who admit
they still have active XP installations.

For Linux there are hardly any practical constraints: it is easy to keep
virtual machines with very old Ubuntu versions around. That version is
relevant for the baseline of libc/libc++ that is compiled into our
Isabelle components. Moving ahead too quickly has no particular purpose,
but it cuts off some long-term Linux installations (e.g. on servers).

Mac OS / Mac OS X / OSX / macOS is most difficult to support, because it
changes a lot and real Apple hardware is required to run it. Moreover,
Apple systematically phases out old hardware when new OS versions are
released. (These policies partially explain why Apple has become a black
hole that sucks up more and more wealth of the planet.)

> In this case I recommend to bump the baseline for Ubuntu up to 14.04 LTS
> (or even 16.04 LTS).

How did you get to that conclusion? Ubuntu LTS support lasts 5 years.
Empiricially, I've seen the last 3 LTS versions being installed by
Isabelle users. Consequently, we have only recently dropped 10.04 LTS
and are now at 12.04 LTS for some years to come.

> And secondly dropping support for OS X Mavericks, since that is also
> unsupported by Apple right now.

Dropping Mavericks now would mean to reinstall macbroy2, which is our
main witness for non-trivial Apple hardware. Such a change comes with
the risk that the system stops working afterwards: the old saying "never
change a running system" has some truth in it.

The recent update of macbroy30 to Sierra has again demonstrated how
fragile long-running Apple hardware actually is.


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