[TCLCORE] Tk Aqua future on Tiger

[<dg...@ni...>]

I wanted to offer a possible support
path for those with users on Tiger
(Mac OSX 10.4) who wish to use Tcl 8.6,
and need to use Tk Aqua as well.

As recently mentioned here, the plan is
for Tk Aqua version 8.6 to shift to an
implementation on Cocoa, and the new
implementation also adds a requirement of
at least Leopard (Mac OSX 10.5).  Those
still using Tiger would be left with
only Tk 8.5.* to work with.

My sense is that the biggest problem with
this situation for the Tiger users is that
by getting stuck with Tk 8.5.*, the
implication is that they are also stuck
with Tcl 8.5.* and have to give up the
new features arriving in Tcl 8.6.  This
is especially unwelcome for developers who
have been working with Tcl 8.6 features in
alpha/beta state and have come to rely on
them.  My sense (possibly completely wrong)
is that there is much less loss within Tk
itself getting stuck with version 8.5.  Meaning
no disrespect to those who have added features
to Tk 8.6, there's just not a large number
of them, especially when specifically considering
their impact in a Tiger environment (corrections
welcome).

So, from that perspective, the key step to mitigate
the loss to Tiger users is to break the linkage
between Tk 8.5 and Tcl 8.5.  That's what Tk Patch
2794032 does.  Apply it to the core-8-5-branch of
Tk and the resulting sources produce a Tk 8.5 library
that will happily [load] into a Tcl 8.6 interp.

The patch is simple.  All it is doing is removing
some defensive programming which forbade that combination
based on a principle of an abundance of caution that
changes in Tcl 8.6 *might* break Tk 8.5.  We're late
enough in Tcl 8.6 development now to have good
confidence that's not going to happen, so a Tk 8.5
that assumes [load]ing into any Tcl 8.5+ interp will
work makes sense.

With Patch 2794032 applied and a Tk 8.5.8 release
containing it, then a script application that needed
to continue to support Tiger could do so with a

   package require Tk 8.5.0-8.6

when the app detects it is running on Tiger and just

   package require Tk 8.5.0

in other environments.  The special requirement for
Tiger is only necessary as protection against a Tk 8.6
that might somehow get installed on a Tiger system
even though it doesn't work there.  An app willing
to risk an assumption that won't happen could get
by with no changes at all.

Hope that's a useful contribution to the controversy.

DGP