Add a “clean GameData” button to the toolbar

[JonnyOThan]

One of the biggest stumbling blocks for people using CKAN is that it can’t detect when a mod has been manually deleted*. That’s a hard problem to solve, but a really common cause of this issue is when someone deletes everything from their GameData folder without uninstalling things from CKAN.

It might reduce issues if we add a button in CKAN that will uninstall all mods and then delete all non-stock files from GameData (possibly excluding zip files). After a confirmation dialog of course.

Also probably needs a better name considering ksp2, or the name could be different depending on the game.

Maybe a toolbar button isn’t the right place, but putting it in a menu somewhere would be far less discoverable and this option is only helpful as long as users know about it.

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* This can cause errors later because CKAN will not reinstall those mods if a new mod is installed which depends on them. In my experience this is one of the biggest factors that give people the impression that CKAN messed up their install

[JonnyOThan]

example of the kind of problem that this could avoid: https://www.reddit.com/r/KerbalSpaceProgram/comments/1akzguu/endless_list_of_issues_reported_by_b9_part_switch/

(Note I think manual deletion was NOT actually the cause of this one, but it could have been)

[HebaruSan]

Maybe the Umanaged Files list from #3833 could be updated to also show missing files (and be renamed to suit).

This isn't quite a duplicate of #2090, but we can probably close both together once some work is done on this.

[HebaruSan]

I don't think a manual action would solve anything here. A user that knows enough to go run this tool could just not mess up their GameData in the first place. To make a dent in this kind of user error, we would need something that runs automatically to catch such problems proactively.

Maybe we could do a quick scan for each installed mod, and if any of its files are missing, enable the "upgrade" checkbox to perform a reinstall (much like we already do for installed mods whose metadata has changed as of #3828). That way if someone manually clears their GameData and then runs CKAN and clicks "Update all", it would reinstall everything they just deleted to get back to a valid state.