net40 application with Microsoft.Bcl.Async cannot resolve dependencies

Steps to reproduce

Create a net40 application that references Microsoft.Bcl.Async and uses await: project.csproj:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net40</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Bcl.Async" Version="1.0.168" />
  </ItemGroup>

</Project>

Program.cs:

using System.Threading.Tasks;

class Program
{
    static void Main() => F().Wait();
    static async Task F() => await TaskEx.Delay(100);
}

Start with dotnet run

Expected behavior

Program should start.

Actual behavior

Creates errors

C:\Program Files\dotnet\sdk\1.0.0\Microsoft.Common.CurrentVersion.targets(1964,5): warning MSB3268:
The primary reference "C:\Users\Schoenke\.nuget\packages\microsoft.bcl.async\1.0.168\lib\net40\Micro
soft.Threading.Tasks.dll" could not be resolved because it has an indirect dependency on the framewo
rk assembly "System.Threading.Tasks, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50
a3a" which could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0".
To resolve this problem, either remove the reference "C:\Users\Schoenke\.nuget\packages\microsoft.bc
l.async\1.0.168\lib\net40\Microsoft.Threading.Tasks.dll" or retarget your application to a framework
 version which contains "System.Threading.Tasks, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b
03f5f7f11d50a3a". [C:\Users\Schoenke\Documents\Visual Studio 2017\Projects\NetCoreBCLTest\NetCoreBCL
Test\NetCoreBCLTest.csproj]
C:\Program Files\dotnet\sdk\1.0.0\Microsoft.Common.CurrentVersion.targets(1964,5): warning MSB3268:
The primary reference "C:\Users\Schoenke\.nuget\packages\microsoft.bcl.async\1.0.168\lib\net40\Micro
soft.Threading.Tasks.Extensions.dll" could not be resolved because it has an indirect dependency on
the framework assembly "System.Threading.Tasks, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b0
3f5f7f11d50a3a" which could not be resolved in the currently targeted framework. ".NETFramework,Vers
ion=v4.0". To resolve this problem, either remove the reference "C:\Users\Schoenke\.nuget\packages\m
icrosoft.bcl.async\1.0.168\lib\net40\Microsoft.Threading.Tasks.Extensions.dll" or retarget your appl
ication to a framework version which contains "System.Threading.Tasks, Version=1.5.11.0, Culture=neu
tral, PublicKeyToken=b03f5f7f11d50a3a". [C:\Users\Schoenke\Documents\Visual Studio 2017\Projects\Net
CoreBCLTest\NetCoreBCLTest\NetCoreBCLTest.csproj]
C:\Program Files\dotnet\sdk\1.0.0\Microsoft.Common.CurrentVersion.targets(1964,5): warning MSB3268:
The primary reference "C:\Users\Schoenke\.nuget\packages\microsoft.bcl.async\1.0.168\lib\net40\Micro
soft.Threading.Tasks.dll" could not be resolved because it has an indirect dependency on the framewo
rk assembly "System.Runtime, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" whi
ch could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0". To resol
ve this problem, either remove the reference "C:\Users\Schoenke\.nuget\packages\microsoft.bcl.async\
1.0.168\lib\net40\Microsoft.Threading.Tasks.dll" or retarget your application to a framework version
 which contains "System.Runtime, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
. [C:\Users\Schoenke\Documents\Visual Studio 2017\Projects\NetCoreBCLTest\NetCoreBCLTest\NetCoreBCLT
est.csproj]
C:\Program Files\dotnet\sdk\1.0.0\Microsoft.Common.CurrentVersion.targets(1964,5): warning MSB3268:
The primary reference "C:\Users\Schoenke\.nuget\packages\microsoft.bcl.async\1.0.168\lib\net40\Micro
soft.Threading.Tasks.Extensions.dll" could not be resolved because it has an indirect dependency on
the framework assembly "System.Runtime, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f11
d50a3a" which could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0
". To resolve this problem, either remove the reference "C:\Users\Schoenke\.nuget\packages\microsoft
.bcl.async\1.0.168\lib\net40\Microsoft.Threading.Tasks.Extensions.dll" or retarget your application
to a framework version which contains "System.Runtime, Version=1.5.11.0, Culture=neutral, PublicKeyT
oken=b03f5f7f11d50a3a". [C:\Users\Schoenke\Documents\Visual Studio 2017\Projects\NetCoreBCLTest\NetC
oreBCLTest\NetCoreBCLTest.csproj]
Program.cs(9,40): error CS0103: The name 'TaskEx' does not exist in the current context [C:\Users\Sc
hoenke\Documents\Visual Studio 2017\Projects\NetCoreBCLTest\NetCoreBCLTest\NetCoreBCLTest.csproj]

The build failed. Please fix the build errors and run again.

Environment data

dotnet --info output:

.NET Command Line Tools (1.0.0)

Product Information:
 Version:            1.0.0
 Commit SHA-1 hash:  e53429feb4

Runtime Environment:
 OS Name:     Windows
 OS Version:  6.1.7601
 OS Platform: Windows
 RID:         win7-x86
 Base Path:   C:\Program Files\dotnet\sdk\1.0.0

Side Note: Similar behaviour with Microsoft.Net.Http which fails to resolve System.Net.Http.

[pizixie]

@rguryanov your example maybe work when OutputType is Exe,but Library did not

this problem had be solved in this by @ericstj

just to add

<AppConfig Condition="'$(TargetFramework)' == 'net40'">app.net40.config</AppConfig>
<AutoUnifyAssemblyReferences Condition="'$(TargetFramework)' == 'net40'">false</AutoUnifyAssemblyReferences>

app.net40.config like below:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-2.2.29.0" newVersion="2.2.29.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-2.6.10.0" newVersion="2.6.10.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Threading.Tasks" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-2.6.10.0" newVersion="2.6.10.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
</configuration>

[rguryanov]

One workaround for that problem. Add import to Microsoft.Bcl.Build.targets in .csproj: <Import Project="..\Microsoft.Bcl.Build.targets" Condition="Exists('..\Microsoft.Bcl.Build.targets')" /> File Microsoft.Bcl.Build.targets can be found in packages\Microsoft.Bcl.Build.1.0.14\tools\Microsoft.Bcl.Build.targets when you install Microsoft.Bcl.Async nuget in classic windows desktop app.

And add App.config to project (in vs add-> new item-> application configuration file):

<?xml version="1.0" encoding="utf-8"?>
<configuration>
	<runtime>
		<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
			<dependentAssembly>
				<assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
				<bindingRedirect oldVersion="0.0.0.0-2.6.8.0" newVersion="2.6.8.0" />
			</dependentAssembly>
			<dependentAssembly>
				<assemblyIdentity name="System.Threading.Tasks" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
				<bindingRedirect oldVersion="0.0.0.0-2.6.8.0" newVersion="2.6.8.0" />
			</dependentAssembly>
		</assemblyBinding>
	</runtime>
</configuration>

When you target multiple frameworks do remember to change condition for import and App.config. For example to something as

<Import Project="..\Microsoft.Bcl.Build.targets" Condition="Exists('..\Microsoft.Bcl.Build.targets') AND '$(TargetFramework)' == 'net40'" />
<ItemGroup Condition="'$(TargetFramework)' != 'net40'">
	<None Remove="app.config" />
</ItemGroup>