How to reproduce:
1. Create a new Unity project.
2. Create a new empty C# script and open it.
3. Click the "Play" button in Visual Studio to debug.

Expected result: The debug succeeds without any errors.
Actual result: The debug fails with many errors. Errors say they could not find files in "Packages" subfolders in the project. Opening "Packages" through Finder shows there are no subfolders in the mentioned folder.

Reproducible with - 2018.1.0b3, 2018.1.0b11, 2018.2.0a5
Not reproducible with - 5.6.2p1, 5.6.5p3, 2017.1.0f1, 2017.1.3p2, 2017.2.0b1, 2017.2p1, 2017.3.2f1, 2018.1.0a4, 2018.1.0b2
Could not test with:
- 5.6.0a1, 5.6.2f1, 2017.1.0a1, 2017.1.0b10, 2017.2.0a1, 2017.2.0a4 (could not find "Create->C# Script" in the context menu. Creating scripts by adding it as a new component to a prefab did not help either - scripts were not shown in the Project window or in the inspector window as a component (though it was created in the folder)).
- 2018.1.0a1, 2018.1.0a3 (Visual Studio showed error "Predefined type 'System.Void' is not defined or imported (CS0518)" on default 'Start' and 'Update' methods).

Note:
For 2018.1.0b3-2018.1.0b8 there is no "Packages" folder in the project folder, but error messages still mention it.
For 2018.1.0b9-2018.1.0b11, 2018.2.0a1-2018.2.0a5 the "Packages" folder is in the project folder, but it only contains the "manifest.json" file.

Verified with: version 2018.1.0b12 and version 2018.2.0a6