Add Package Collections for Content Curation

[Montandalar]

Problem

Users may often want to download a set of related content e.g. different trains for advtrains, different vehicles by APercy, a few different mobs to populate their world with etc. Users also benefit by curators creating good sets of compatible mods.

The existing approach for content curation consists of either creating another "game" that is based on Minetest Game, or a modpack. Both have a large maintenance burden. The game or modpack author has to update every mod individually and restructure modpack directories to avoid nested modpacks. Game authors must also update the mods that are a part of their base game. Even a modpack that just wanted to bundle advtrains with basic_trains would have to restructure those two modpacks to avoid nesting before distributing them on ContentDB. Those mods also don't logically belong in a modpack - people just want to install them together sometimes, for instance "Blockhead's Favourite Trains" is not a good modpack idea, but it is a good collection idea. Also, if there was also a texture pack that the curator wanted users to use, they would have to ask people to separately install that, because it can't go inside the modpack. It would be better to have a way for a user to ask for collections of packages to be installed at once.

ContentDB does have functionality to automatically install dependencies, but this doesn't make it easy to install several content packs for one base mod, just like trains, vehicles or mobs as previously mentioned.

Solutions

The Steam Workshop allows users to create "collections", which identifies multiple Workshop items to all be downloaded (subscribed to) at once. These are popular for distributing mods along with their dependencies, which ContentDB handles another way. But another outcome of this system is that content curators can create a set of curated content to be used together. Also, unsubscribing from a collection removes any of its dependencies that aren't individually subscribed to.

To help content curators create and to help players follow recommendations more easily, ContentDB should allow signed-in users to create Collections. Collections will designate versions of packages to be installed together. There should also be a system to notify Collection maintainers that there are updates to mods in their collection.

When browsing the Collections section, users can see all packages in a collection and their versions, plus the usual images, textual description, ratings, comment threads and versions that are attached to any other package. When installing in-game, the Minetest client should offer to download all of the packages automatically, and warn if there is a version difference on any version of any of the packages installed as compared to the one in the collection. Note how the language is content-type agnostic: Mods, Games and Texture Packs could all be part of collections.

The Steam Workshop mandates updates; often Garry's Mod, for instance, will automatically update all versions of all content as soon as you open the game, or even before it, depending on Steam update settings. ContentDB's collection system should probably not force updates, as many people manually manage their mods in Minetest. However, Collections should be shown in the in-game ContentDB browser as Collections, and users should be able to update their version of the collection.

Users should be able to remove Collections. This will remove any mod that was only installed because of its inclusion in a collection, but leave manually installed packages alone. This will necessitate tracking much like other package managers of what is manually installed and what is only installed as a dependency; ContentDB has a file in each mod directory for purposes like this I think?

Alternatives

Continue to only accept modpacks and games on ContentDB, and push the burden of maintenance and marketing back onto curators/modpack authors, as well as leave the overall discoverability of content on ContentDB at its current, but lower, value.' This would be more viable if the engine were to support nested modpacks.

Additional context

This change would affect both this repository and minetest/minetest.

Collections could include any packages at all from ContentDB. For instance, "Minetest Game Jam 2021" could be a collection as well. Some combinations of packages wouldn't make sense: "Soothing 32" together with "Snake 3D" wouldn't make sense together; but I think it is up to the Collection author to make sure their Collection makes sense. Also, some collections would just be "my stuff" type collections, for instance for a person to be able to install their favourite content on any device with only a few steps. That's okay - the rating system will make better collections show up over those types of collections anyway.