fix loading of custom style.kv

[Gobbel2000]

Adding a custom resource directory using kivy.resources.resource_add_path(path) did not load the customized style.kv in the program directory because the added resource path was overwritten by the following line in kivy/lang/builder.py: Builder.load_file(join(kivy_data_dir, 'style.kv'), rulesonly=True) Here, style.kv is hardcoded to the directory of the default style.kv, bypassing the logic of kivy.resources.resource_find(filename).

This question suggests to load the custom style.kv directly using kivy.lang.Builder.load_file() as a workaround. This works, but also means both, the custom and default style.kv are parsed. This can create re-decleration warnings (e.g. [WARNING] [Factory ] Ignored class "FileIconEntry" re-declaration.) and potentially break popups (kivy.uix.popup.PopupException: Popup can have only one widget as content).

In kivy/resources.py a default resource_paths list is created. Instead of adding the kivy_data_dir, including style.kv, the kivy module root directory is added twice. I changed that so that in case there is no custom style.kv given the default one is found by kivy.resources.resource_find(filename).

I tested this with no custom style.kv, with the custom one in the program directory, and with a custom style.kv in an outside directory, added via kivy.resources.resource_add_path(path). Everything seems to work as expected. Only thing to note is that in the last case the call to resource_add_path() must happen before importing kivy.app which already wants to read style.kv.

[welcome[bot]]

Thanks for opening your first pull request here! 💖 Please check out our contributing guidelines.

[matham]

A better way, without these changes, is before you load your custom style.kv unload the builtin style.kv.

I don't think this PR is a good idea, because with the change when kivy tries to load style.kv, it could load any style.kv file including one not intended by the user (e.g. if they have a different style.kv that is not meant to replace the builtin one but just happens to have the same name).

We have talked about splitting kivy's style.kv into smaller files that can be somehow optional or overwritten, but no one has actually implemented that. That would be a long term solution for the problem though.

[Gobbel2000]

I see, style.kv is probably a popular filename to use. For now, removing the note to style.kv in the resources documentation might be a good measure.