Project A referencing package B via AssetTargetFallback, doesn't use that same AssetTargetFallback to pull B's dependency package C

[AArnott]

@nkolev92 edit:

• Design - AssetTargetFallback is respected with dependency resolution #11460
• Implementation - conditional on design approval - Consider AssetTargetFallback when selecting transitive project/package dependencies  NuGet.Client#4372

---

When I added netcoreapp2.0 as a target for my console application, it failed at runtime because it couldn't find an assembly that was a transitive dependency of one of my package references. When I add the package reference explicitly, it works fine. I inspected the VSMefSample.deps.json file and found that there is no mention of the transitive dependency until I add it as a direct dependency.

It would seem then, that dotnet restore (or equivalent in VS) is not fully restoring transitive dependencies when it tries to see through net45 packages to adapt them to work on netcoreapp2.0.

Repro

git clone https://github.com/AArnott/VSMefSample
cd VSMefSample
git checkout ce6bef7cc49d0c0c15b2da322ef2a78b86e6d178
cd VSMefSample
dotnet restore
dotnet run -f netcoreapp2.0

Expected

dotnet run -f netcoreapp2.0
C:\Users\andarno\source\repos\VSMefSample\VSMefSample\VSMefSample.csproj : warning NU1701: Package 'Microsoft.VisualStudio.Composition 15.3.38' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project.
C:\Users\andarno\source\repos\VSMefSample\VSMefSample\VSMefSample.csproj : warning NU1701: Package 'Microsoft.VisualStudio.Composition 15.3.38' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project.
Tree
   Apple (IsJuicy: True)
   Apple (IsJuicy: False)
   Pear (IsDelicious: True)

Actual

dotnet run -f netcoreapp2.0
C:\Users\andarno\source\repos\VSMefSample\VSMefSample\VSMefSample.csproj : warning NU1701: Package 'Microsoft.VisualStudio.Composition 15.3.38' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project.
C:\Users\andarno\source\repos\VSMefSample\VSMefSample\VSMefSample.csproj : warning NU1701: Package 'Microsoft.VisualStudio.Composition 15.3.38' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project.

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.VisualStudio.Validation, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
   at VSMefSample.Program.Main(String[] args)

Version info

dotnet --info
.NET Command Line Tools (2.0.2-vspre-006949)

Product Information:
 Version:            2.0.2-vspre-006949
 Commit SHA-1 hash:  23fc6ec23d

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.15063
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.0.2-vspre-006949\

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0
  Build    : e8b8861ac7faf042c87a5c2f9f2d04c98b69f28d

[rrelyea]

Assigned to @mishra14 in backlog as P1. Seems like ATF should work identically to non-ATF restores.
cc @emgarten

[mishra14]

@AArnott are you still facing this issue with latest VS preview build?

[AArnott]

@mishra14 Yes, it still repros with the latest int.preview build:

dotnet --info
.NET Command Line Tools (15.5.0-preview-007044)

Product Information:
 Version:            15.5.0-preview-007044
 Commit SHA-1 hash:  278cbf6c44

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.16299
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\15.5.0-preview-007044\

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.3
  Build    : a9190d4a75f4a982ae4b4fa8d1a24526566c69df

[rrelyea]

retitled: Project A referencing package B via AssetTargetFallback, doesn't use that same AssetTargetFallback to pull B's dependency package C

@AArnott likely had a scenario where A called an API in B and B called an API in C so he ran into a runtime issue.
When I tried creating the same situation...and had A call B and C, it was a compile time error.

[rrelyea]

@nkolev92 - please address...this is likely more important with netcoreapp3 increased usage.
if you can balance to a new member of team, that is fine also.

[rrelyea]

workaround is to manually reference C as a top level package reference, I believe.

[clairernovotny]

Bump?

[KirillOsenkov]

This is a major adoption blocker for .NET and causing unnecessary friction in the ecosystem. Would be nice to prioritize this please.

@clairernovotny do you know anyone on the NuGet team who could perhaps champion this? ;)

[nkolev92]

Design out at #11460.

Once that's been reviewed and approved, NuGet/NuGet.Client#4372 is merge quality already.

[nkolev92]

This should land in 6.2/6.0.200/17.2.

Not inserted yet, but should be in preview 1 of 17.2