Please improve plugin dependency handling

[rbri]

While testing the latest RC build (RC3), the djvu plugin was missing from the list of installed plugins. This was simply because i missed the required djvu libs. After installing them the plugins are back.

I like to suggest:

• the list of plugins should contain a list of all detected plugins
• if the installation of a plugin fails, the dialog should list this plugin together with a (hopefully helpful) error message

[Lewis Rosenthal]

I was going to dupe this over to #282, but that ticket itself is now dated (Poppler is not the only plugin with external dependencies). I will dupe that one here, as this is a more general ticket.

Yes, we need to better address these during install, as well (I am working on the WIS for Lucide, now).

I think that in your last bullet point above, you mean "if the loading of a plugin fails," rather than the installation of a plugin.

In #282, I proposed an error dialog such as:

Unable to load PDF Plugin.
Possible reason: Incompatible poppler library.

Please install poppler-0.42.0 to enable PDF rendering.

Would this address your first bullet point, Ronald, or do you see us needing more specific help, e.g.:

Click here to launch ANPM to install <blah>

(I don't think this is a good idea, but I am just mentioning it for purposes of illustration)?

[rbri]

I think that in your last bullet point above, you mean "if the loading of a plugin fails," rather than the installation of a plugin. Correct.

I also think your suggested error message is sufficient. We have a detailed readme with installation instructions.

We have to think about the way we will show the error. From my point of view the check has to be done at application start. Let's assume only the djvu plugin is not available. Does it make sense to show an error dialog if i like to open a pdf file?

I think the error info should be always available from the plugin dialog (as i already mention in the ticket itself). Maybe there is a way to figure out, if a plugin is available for the file type but the loading of the plugin failed. In this case i think we have to present a error dialog.

And an error dialog is also a good idea if there is no plugin available/loadable at all.