[Gtk2hs-devel] Error when adding nodes to a tree store in response to testExpandRow

[Donald A. <don...@gm...>]

I've written a personal finance manager, having become dissatisfied
with Gnucash after many years of use. My own system, Newcash, is
written in C/GTK3/Sqlite3 (I will be making it available via github
when the documentation is ready). In recent months, I've become
interested in Haskell (I've written a lot of Lisp and Scheme code over
the years) and I re-wrote the Newcash report generator (originally
written in Python to process Gnucash's xml file and thus was pretty
ugly and needed re-writing) in Haskell. Enthusiastic about the
language and pleased with the performance of the report generator, I
decided to experiment with re-writing Newcash itself in Haskell, for
all the reasons that Haskell is to be preferred to C.


But I've run into a show-stopper. Here's the situation: the Newcash
initial window displays the tree of accounts. Not wanting to endure
long startup times (a big issue with Gnucash), I initially want to
populate the tree model with the root, its children, and its
grandchildren. The root gets expanded, so the children are visible,
but the grandchildren are present, so the children are expandable. A
callback is set up to handle the TreeView's testExpandRow signal,
indicating that the user has requested expansion of one of the nodes.
I do this initial setup of the accounts window prior to calling
mainGUI the first time. This all works fine.


The trouble starts if I try to expand one of the root's children by
clicking it. The root's grandchildren are already present, but
callback attached to the testExpandRow needs to add the grandchildren
of the clicked node, so that if it has children, it will appear
expandable. The callback receives both an iter and a path to the
clicked node. It uses the path in a loop that adds the grandchildren
of the clicked node to the TreeStore. This succeeds, but when the
callback returns, I get an error message:


** (Newcash:920): CRITICAL **: gtk2hs_store_iter_has_child: assertion
'iter->stamp == store->stamp' failed

and the display fails to refresh, with the clicked node expanded. If I
click the same node again, it expands correctly (the grandchildren are
already present, courtesy of the response to the previous click).

I'm guessing that the iter being passed to the callback (which I don't
use; as mentioned before, the insertion of the grandchildren is done
using the path derived from the path of the clicked node, using
treeStoreInsert) has a time-stamp as of the time the first
testExpandRow signal was issued. In response to that signal, I add
some nodes to the store. I'm guessing that doing so updates the
time-stamp on the store and that the two time-stamps are compared upon
return from signal processing, and they are no longer equal. The
second click does nothing to the store (my callback is smart enough to
know that a node has already been processed and doesn't add its
grandchildren twice), so the second time the node is clicked, the
time-stamp comparison works.