How to prevent the same file to be added in the playlist multiple times?

[johnmapeson]

And the second question:

If I click test1 or test2 in the sidebar multiple times, it will be added to the playlist again and again. How to prevent this?

[kode54]

Unless you're proposing that clicking the sidebar always replaces the entire playlist, I'd have to run a duplicate track check on the playlist every time it's clicked on. And which duplicates should be removed? What if a user wants duplicates?