If you select an entry in the saved sessions list box, but without
double-clicking to actually load it, and then you hit OK, the config-
box code will automatically load it. That just saves one click in a
common situation.
But in order to load that session, the config-box system first has to
ask the list-box control _which_ session is selected. On Windows, this
causes an assertion failure if the user has switched away from the
Session panel to some other panel of the config box, because when the
list box isn't on screen, its Windows control object is actually
destroyed.
I think a sensible answer is that we shouldn't be doing that implicit
load behaviour in any case if the list box isn't _visible_: silently
loading and launching a session someone selected a lot of UI actions
ago wasn't really the point. So now I make that behaviour only happen
when the list box (i.e. the Session panel) _is_ visible. That should
prevent the assertion failure on Windows, but the UI effect is cross-
platform, applying even on GTK where the control objects for invisible
panels persist and so the assertion failure didn't happen. I think
it's a reasonable UI change to make globally.
In order to implement it, I've had to invent a new query function so
that config.c can tell whether a given control is visible. In order to
do that on GTK, I had to give each control a pointer to the 'selparam'
structure describing its config-box pane, so that query function could
check it against the current one - and in order to do _that_, I had to
first arrange that those 'selparam' structures have stable addresses
from the moment they're first created, which meant adding a layer of
indirection so that the array of them in the top-level dlgparam
structure is now an array of _pointers_ rather than of actual structs.
(That way, realloc half way through config box creation can't
invalidate the important pointer values.)
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