Plugin template does not work with TypeError

[cozzyd]

Describe the bug

I try to compile the plugin template, which links properly, but when I try to import, it fails with: TypeError: Could not create type 'MyModule' as base 'crpropa::Module' has not been initialized.

This is with the latest release of

Is the bug related to the physics in CRPropa?

No.

To Reproduce

cd plugin-template
mkdir build
cd build
cmake ../
make
python ../testPlugin.py 

Expected behavior I expect the testPlugin to import without issue.

System (please complete the following information):

• Operating system: Fedora 32
• Laptop or computing cluster? Desktop...
• Python version: 3.8.5
• Swig version: 4.01
• Cmake version: 3.17.4
• GCC version: 10.2.1

Additional context

crpropa otherwise works fine. As far as I can tell, this fails with both the release and master branches.

[TobiasWinchen]

Hi,

I can reproduce the issue. Please try to first import crpropa, and then the plugin, which works for me:

In [1]: import myPlugin
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

[...]
TypeError: Could not create type 'MyModule' as base 'crpropa::Module' has not been initialized.

In [2]: import crpropa

In [3]: import myPlugin

In [4]: 

However, this import should be done ideally automatically, or at least this should be added to the documentiaton.

[cozzyd]

Hi Tobias,

That does not work for me (in fact, testPlugin.py already imports crpropa first).

However, looking at the generated SWIG code for the test plugin, I see:

#define SWIGPYTHON_BUILTIN

I'm not sure exactly what that means, but crpropa was apparently configured (automatically) without ENABLE_SWIG_BUILTIN for me. If I turn on ENABLE_SWIG_BUILTIN, then the plugin works.

[TobiasWinchen]

OK - Not enabling swig builtin is the current default due to a swig bug: https://github.com/CRPropa/CRPropa3/issues/264, which is supposed to be fixed only in 4.0.2. however, we probably still should adapt the plugin.

[cozzyd]

I see, yeah, the plugin "worked" with builtin enabled, but it's broken in current swig. It seems like just taking -builtin out of the CMakeLists.txt (line 35) for the plugin template is sufficient to make it work properly for now. I guess ideally you'd want it to pick up whether or not it should use builitin from the crpropa installation itself. This could probably be done inside findCRPropa.py by adding a crpropa.useSwigBuiltin(), although there are probably simpler ways to do it.

[lukasmerten]

I guess we can close this issue with the adaptions introduced in #466 and because swig 4.0.2 became more or less available wide spread. If the problem persists please reopen the issue.