resharper-unity: Rider does not install plugin into Unity Project, no `sln` file generated.

Hello,

I’m trying to use Rider 2018.1.2 with Unity 2018.1.4f1 on macOS 10.13.5, and it looks like Rider is not properly installing the Unity plugin into the Unity project.

This is a clean installation of both applications on this machine. I’ve already used Unity with MonoDevelop on macOS on another machine, and I already use several IntelliJ-derived IDEs on this machine where I’m experiencing the issue.

I’ve installed Unity without Visual Studio for Mac, because I figured that I wouldn’t need it since I’m going to use Rider instead. A possibly related side effect is that creating a new project in Unity (or opening a stock project, e.g. the standard assets project that comes bundled with the installation), will not create a .sln file. I’m not sure if this is normal.

Without the .sln file I can’t have Rider open the Unity project as recommended in the docs (one, two), so I resorted to open the entire Unity project directory using:

Rider Splash Screen > Open Solution or Project

With that, Rider opens and indexes the project and it generates a new .sln file, but it doesn’t look like the integration is set up:

1. there is no Unity icon in the lower-right corner in the Rider status bar;
2. there are no special Unity buttons in the toolbar;
3. the other editor integrations don’t seem to be there;
4. Rider is not auto-configured as the external editor;
5. There is nothing in the Assets/Plugins/ directory of the project.

Interestingly, the Unity Explorer project view is available:

Any idea of what’s happening? If it’s just a matter of installing Unity with Visual Studio for Mac, possibly it would be better to say so in the docs.

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Possibly related to this: https://github.com/JetBrains/resharper-unity/issues/387