为什么NuGet会下载看似不必要的依赖项？

Question

安装System.Collections.Immutable NuGet时会下载诸如System.Runtime之类的程序集，尽管我已经安装了.NET 4.6.1中的该程序集。

另外，在lib目录下的目录（例如packages\System.Runtime.4.0.0\lib\net45）不包含dll文件，只是称为_._的空文件。

这是为什么？这是必要的吗？我错过了什么？

NuGet日志：

Install-Package System.Collections.Immutable -Version 1.1.37
Attempting to gather dependency information for package 'System.Collections.Immutable.1.1.37' with respect to project 'ConsoleApplication1', targeting '.NETFramework,Version=v4.6.1'
Attempting to resolve dependencies for package 'System.Collections.Immutable.1.1.37' with DependencyBehavior 'Lowest'
Resolving actions to install package 'System.Collections.Immutable.1.1.37'
Resolved actions to install package 'System.Collections.Immutable.1.1.37'
  GET https://www.nuget.org/api/v2/package/System.Collections/4.0.0
Installing System.Collections 4.0.0.
Adding package 'System.Collections.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Collections.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Collections.4.0.0' to 'packages.config'
Successfully installed 'System.Collections 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Diagnostics.Debug/4.0.0
Installing System.Diagnostics.Debug 4.0.0.
Adding package 'System.Diagnostics.Debug.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Diagnostics.Debug.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Diagnostics.Debug.4.0.0' to 'packages.config'
Successfully installed 'System.Diagnostics.Debug 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Globalization/4.0.0
Installing System.Globalization 4.0.0.
Adding package 'System.Globalization.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Globalization.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Globalization.4.0.0' to 'packages.config'
Successfully installed 'System.Globalization 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Linq/4.0.0
Installing System.Linq 4.0.0.
Adding package 'System.Linq.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Linq.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Linq.4.0.0' to 'packages.config'
Successfully installed 'System.Linq 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Resources.ResourceManager/4.0.0
Installing System.Resources.ResourceManager 4.0.0.
Adding package 'System.Resources.ResourceManager.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Resources.ResourceManager.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Resources.ResourceManager.4.0.0' to 'packages.config'
Successfully installed 'System.Resources.ResourceManager 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Runtime/4.0.0
Installing System.Runtime 4.0.0.
Adding package 'System.Runtime.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Runtime.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Runtime.4.0.0' to 'packages.config'
Successfully installed 'System.Runtime 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Runtime.Extensions/4.0.0
Installing System.Runtime.Extensions 4.0.0.
Adding package 'System.Runtime.Extensions.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Runtime.Extensions.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Runtime.Extensions.4.0.0' to 'packages.config'
Successfully installed 'System.Runtime.Extensions 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Threading/4.0.0
Installing System.Threading 4.0.0.
Adding package 'System.Threading.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Threading.4.0.0' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Threading.4.0.0' to 'packages.config'
Successfully installed 'System.Threading 4.0.0' to ConsoleApplication1
  GET https://www.nuget.org/api/v2/package/System.Collections.Immutable/1.1.37
Installing System.Collections.Immutable 1.1.37.
Adding package 'System.Collections.Immutable.1.1.37' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Collections.Immutable.1.1.37' to folder 'd:\workspace\ConsoleApplication1\packages'
Added package 'System.Collections.Immutable.1.1.37' to 'packages.config'
Successfully installed 'System.Collections.Immutable 1.1.37' to ConsoleApplication1

- Kalevi

Answer 1

我认为这是由于dotnet core/cli带来的变化。在donet core中，维护依赖链比以前更加重要，因为你没有完全安装的框架。这就解释了为什么lib\net45文件夹为空，因为它们是安装在计算机上的BCL的一部分，实际上没有任何东西需要包含进去。

- CodingGorilla