Rescanning the local S2 media provider merges playlists

[daladim]

🌎 Environment

S2 built from sources (current main branch)

💬 Description

Rescanning the local S2 media provider merges playlists instead of replacing them

🦶 Reproduction Steps

1. Have a stuff.m3u on the disk, with this content

   A/a.mp3
   B/b.mp3
   C/c.mp3
   

2. Add a S2 Media Provider
3. It successfully imports a playlist named stuff, with these 3 items
4. On the disk, modify stuff.m3uso that it now contains

   A/a.mp3
   D/d.mp3
   C/c.mp3
   

5. In S2, click Rescan

Expected result (I think): The stuff playlist now contains the items as they are on the disk, because we've just scanned the disk

Actual result: The stuff playlist contains a merged version of the previous content and the one from the disk:

• A
• B
• C
• D

[daladim]

Expected result is not very clear actually. @timusus , what is the "rescan" philosophy after all? The code has a great support for "updating" scanned playlists instead of bluntly replacing them (see e.g. MediaImporter.PlaylistUpdateData). Is this on purpose?

The described behaviour looks like a bug to me, but maybe there are other workflows where this is actually expected? 🤔

Edit: totally removing the S2 Media Provider before adding it again "correctly" imports the stuff playlist with its content from disk. Am I supposed to use this workflow instead? In this case, should we rephrase the "rescan" button (or description) to explain the difference between removing/adding the provider again?

[timusus]

There is a deliberate effort to ensure that playlists don't get overwritten during a scan.

I haven't thought about this for some time.. The worry is that you might import a playlist - so it's no longer based on its 'm3u' source, but is now just a 'local' S2 playlist. Then, if you make changes to it, you might not want those changes overwritten when you rescan your library.

One possible solution would be to provide this option as a checkbox.. some sort of UI to indicate whether you want to 'merge' or 'replace'..