dotnet-clean and project.assets.json in 2.0

[sstevenkang]

I would like to know why "dotnet clean" depends on project.assets.json file. This new behavior in 2.0 is something we can work around, but I would like to understand why this change in behavior was introduced and what is the project structure expectation of dotnet cli.

Is multiple .csproj files in a single directory not supported/encouraged?

Steps to reproduce

In our project, we have this folder structure for historical reasons:

/obj
/bin
/src
Project.Net35.csproj
Project.Net45.csproj

Pre 2.0, we used to do following commands in sequence:

# build net35
dotnet clean Project.Net35.csproj
dotnet restore Project.Net35.csproj
dotnet build Project.Net35.csproj

# build net45
dotnet clean Project.Net45.csproj
dotnet restore Project.Net45.csproj
dotnet build Project.Net45.csproj

Both .csproj are in the new vs2017 csproj format that starts with <Project Sdk="Microsoft.NET.Sdk">

Expected behavior

The above folder structure worked pre-2.0 because "dotnet clean" command did not take a dependency/make a reference to project.assets.json file and succeeded.

Actual behavior

With 2.0, we see the following error message during dotnet clean:

C:\Program Files\dotnet\sdk\2.0.0\Sdks\Microsoft.NET.Sdk\build\Microsoft.PackageDependencyResolution.targets(165,5): error : Assets file 'd:\workspace\Project\obj\project.assets.json' doesn't have a target for '.NETFramework,Version=v4.5'. Ensure that restore has run and that
you have included 'net45' in the TargetFrameworks for your project. [d:\workspace\Project\Project.Net45.csproj] [
d:\workspace\build.proj]

I think we can workaround this by specifying different obj directory per project or doing dotnet restore -f before dotnet clean. Ideally, we would build for both frameworks in a single .csproj, but it's not something we can invest time in currently.

Environment data

dotnet --info output:

.NET Command Line Tools (2.0.0)

Product Information:
 Version:            2.0.0
 Commit SHA-1 hash:  cdcd1928c9

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.0.0\

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0
  Build    : e8b8861ac7faf042c87a5c2f9f2d04c98b69f28d

[mishra14]

@sstevenkang you are facing this problem because you have 2 different csproj files in the same folder. You can workaround this by adding a --Force to the restore calls which will result in rewriting of the assets file each time.

Related issue: NuGet/Home#6114