Prevent node types and their CCK data being deleted when disabling module

There's actually a combination of things happening here. When uc_product is disabled, hook_node_info() no longer has a record of that node type. When this happens CCK deletes the fields that were attached to the node type. This was brought up some time back at #196042: Field instances are deleted when node type modules are disabled, should wait until they are uninstalled

So yeah. Big, old problem.

It's actually not any hooks that are doing it. When the module list form is submitted, it calls node_type_rebuild(). This function takes all the node types that are marked "disabled" (which happens because they aren't in hook_node_info() anymore) and calls node_type_delete(). This in turn calls hook_node_type(), which CCK uses to delete all of its data, because it's been told that that node type doesn't exist any more.

Using hook_disable() to relinquish control of the product node types is my plan, but only as a stop-gap measure. I'm also going to try to take them back with hook_enable(), but I can see that being tricky.

Just to make it clear, the nodes aren't gone. It's the CCK data that was added to them. Even if they were just "product" nodes, the same thing would happen. This problem affects all modules that implement hook_node_info(). I imagine this is part of why node type modules have become passé.

All of the functionality of products come from the use of node hooks: hook_view(), hook_insert(), etc. Each node type knows which module's implementations to use when the hooks are called. When a product class is made the node types in essence are told "Stop using node_view(), node_insert(), and node_update(), and start using uc_product_view(), uc_product_insert(), and uc_product_update()." This is how they get the price fields in the edit form and the "Add to Cart" button on their page view.

In hindsight, using hook_nodeapi() may have been a better design choice. But uc_product was my first Drupal module, so I chalk it up to inexperience. Fortunately, it doesn't seem to be something that can't be changed.

Here's the workaround I've come up with so far. It ended up being more complicated than I thought because I kept running into newly exposed bugs and no-longer-valid assumptions in the code. I think I've covered all the usual situations, but I'm sure someone can pop my bubble easily.

There's one case I'm not sure what to do about. The theoretical steps go thusly:

• Create a product class that has the same name as some module's node type.
• Disable Ubercart, changing the node type's module to node.
• Install the other module, which takes over the node type.
• Enable Ubercart again.

At best, there's an extra row in {uc_product_classes} polluting the database. At worst, Drupal doesn't know what to do with that node type any more. Any ideas?

I'd really like to be able to rely on users to know what they're doing and clean up after themselves. I'd also like a billion dollars.

Wow. Somehow I managed to go almost a month without realizing I didn't include the patch. Shame on me.

Anyway, I've tested it and it works, but this is certainly the kind of thing that lots of people need to look at.

Well, it's all a moot point now, since CCK no longer deletes its data when node types disappear: #196042: Field instances are deleted when node type modules are disabled, should wait until they are uninstalled
Since no one gave any input on this, I ended up committing that patch anyway.

I suppose it's unnecessary now, but I'm not sure I will actually roll it back. Maybe only for the 2.x version.