Background

Sometimes a mod needs some functionality to be provided by a third party dependency, and there are several choices available, but they have different APIs, so the dependent mod has to implement support for each one separately.

For example, TextureReplacer, TextureReplacerReplaced, SigmaReplacements-SkyBox, and DiRT can all be used to replace the stock SkyBox with a custom one, but they're all mutually incompatible and so a dependent mod has to implement support for them separately one by one.

The provides property can't handle this (well), since there is no baseline abstract concept that they could sensibly provide. Consider if we had all four of the above mentioned mods provide something like SkyBoxReplacer; then we would not have a solution for a dependent mod that only implemented compatibility with 2 or 3 of them. We would need one provides tag for each possible permutation of supports that a mod could implement, which would be unworkable.

Changes

NOTE: This is a high risk change. Core pieces of RelationshipResolver are modified, which risks breaking common tasks. Please review with care!

Now a new any_of format for relationships is allowed:

    "depends": [
        {
            "any_of": [
                { "name": "SigmaReplacements-Heads" },
                { "name": "TextureReplacerReplaced" }
            ]
        },
        { "name": "ModuleManager" }
    ],

This creates a requirement that can be satisfied by any of the specified modules. If the user installs a module with the above syntax, they are prompted to choose which dependency to use:

$ ~/Downloads/KSP/CKAN/_build/ckan.exe install -c ScottManleyHeadPack-1.0.0.ckan 
Too many mods provide SigmaReplacements-Heads OR TextureReplacerReplaced. Please pick from the following:

1) SigmaReplacements-Heads (Sigma Replacements: Heads)
2) TextureReplacerReplaced (TextureReplacerReplaced)
Enter a number between 1 and 2 (To cancel press "c" or "n".): 
1
About to install...

 * Scott Manley Head Pack 1.0.0 (cached)
 * Sigma Replacements: Heads H_v0.2.4 (cached)

Continue? [Y/n] 


Installing mod "ScottManleyHeadPack 1.0.0"
Installing mod "SigmaReplacements-Heads H_v0.2.4"
Updating registry
Committing filesystem changes
Rescanning GameData
Done!

(It works in GUI too.)

The schema and spec are updated to incorporate this syntax.

RelationshipDescriptor is now an abstract base class (let me know if an interface would be better somehow) with two child classes, ModuleRelationshipDescriptor (formerly known as RelationshipDescriptor) and AnyOfRelationshipDescriptor which models the new syntax and mainly holds a List<RelationshipDescriptor> and multiplexes access to it.

Various tests are updated to instantiate ModuleRelationshipDescriptor now that RelationshipDescriptor is abstract.

A new JsonRelationshipConverter class handles parsing .ckan files, populating lists of RelationshipDescriptor with instances of the appropriate child classes based on the contained properties.

Parts of RelationshipResolver are refactored to handle the new syntax, mainly by calling virtual members of RelationshipDescriptor.

Fixes #2522.

Reverse dependencies fix

Previously if you installed a mod that depended on another mod, but the latest of version of the dependency conflicts with or depends on a different version of the original mod, then you'd get an error.

Now older versions of the dependency will be checked to see whether they're compatible.

Includes tests to make sure this works.

Fixes #1693.

Tests fix

I was still getting the error from #2628, I think because the cache objects in KSPManager weren't being disposed. Now this is added to the affected tests.