Improvements to PR #246 (hiding the "Upload" tab)

[dairiki]

Lying in bed last night, it came to me that a better way to implement the goals of PR #246 was simply to disable the upload, upload-submit, and add_file views on contexts for which File resources are not sdi-addable. (PR #246 just hides the Upload tab, the views are still accessible, even though invoking these views would not be appropriate.)

This PR adds a new view predicate which checks the context to see whether a specific content type is sdi-addable. This predicate is then used to protect the previously mentioned views. (I'm not sure that the name of the predicate, sdi_addable, is the best choice. Suggestions welcome.)

I've also renamed the new function content_type_addable, introduced in #246, to is_sdi_addable to more closely match the name of the view predicate.

[cguardia]

Hey, thanks for taking the time to improve this code. About the predicate name, how about tab_addable_content? That would be more in line with the current names for other management view predicates.

Other than that nit, this looks good to me.

[dairiki]

I’m not sure about the "tab_" in tab_addable_content. The Add UI element is a dropdown button, not a tab. Maybe sdi_addable_content? Or just addable_content?

While we are working out API naming nits: where should the is_sdi_addable predicate function be located? I have initially put it in substanced.folder.util, but now I'm thinking a better location is one level up in substanced.folder (a la substanced.property.is_propertied, substanced.catalog.is_catalogable, and substanced.workflow.is_workflowed.)

[cguardia]

My thinking was that this is like a specialized case of the tab_condition predicate, but I see your point. My vote at this time would be for addable_content.

I agree that substanced.folder might be a better location for the predicate.

[cguardia]

Thanks!

[dairiki]

No problem. Thank you!