[Tile-dev] Tile compatibility policy and the core merge

[Joe E. <jen...@fl...>]

When making incompatible changes to the Tile public API,
I've been trying to follow a policy where the old and new
syntaxes are both supported for at least one release cycle,
then removing the old syntax at a later time.  This is to
avoid the need for "flag day" conversions, where users have
to upgrade all the programs that use Tile as soon as they
upgrade Tile itself.

As it stands right now in Tk CVS HEAD, switching from
Tk<=8.5a5+tile to Tk>=8.5a6 will require a flag day conversion.
So the top priority for Tile 0.8.0 is to act as a transitional
release: it should support the Tile 0.7.X interface as well
as the ttk::* interface provided by the core.  That way
users who wish to do so can upgrade in two easier stages
instead of one hard one.

To make this work, the core API will need a couple changes
as well.

First: the treeview widget needs to come back.  People are
actually using this widget, and the only alternative I can think
of is for them to switch to TkTreeCtrl.  Although TkTreeCtrl can
certainly do all the things that ttk::treeview can (and much,
much more!), it's not that easy to use; and since "ease of use"
is the primary, overriding design goal of the ttk::treeview
widget, I don't think this will be work upgrade strategy.

(Jeff was talking about dropping ttk::dialog, too.  That would
be OK, since the implementation is all in Tcl and can be
distributed separately, but ttk::treeview can't be.)

Next: Ttk_Init() in the core needs to [package provide $something].
Right now, if you load the tile package into an 8.5a6 core,
all heck breaks loose, and I don't know how to fix this yet.
So existing code that says [package require tile] is going
to suffer catastrophic failure unless 8.5a6+ can make this
into a no-op, either by declaring "tile 0.8.0" already
provided or by registering a do-nothing "ifneeded" script.

The stubs mechanism (needed for third-party themes like TileQT)
also uses the package database, which is another reason for
the core to [package provide $something].  I can find a workaround
for this if necessary, though.

And on the subject of third-party themes: Tk 8.5 is definitely
going to require a flag day conversion for them.  This isn't
as big a deal -- there aren't as many themes as there are
applications using Tile, the changes required are minor and
mostly mechanical, and a flag day for themes was on the
Tile 0.8.X roadmap anyway.

It doesn't look like I'll be able to get the theme overhaul
done in time for the December core release, so third party
theme developers should expect two flag days.  Sorry about
that; the release schedules just aren't lined up right.


--Joe English

  jen...@fl...