Feature request: Simple way to express an order-only dependency.

[jhudsoncedaron]

Previously (net core 2.1), this worked:

  <ItemGroup>
    <ProjectReference Include="..\buildtool\buildtool.csproj" Properties="RuntimeIdentifier=">
      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
    </ProjectReference>
  </ItemGroup>

Now, it doesn't, and even all this doesn't work:

  <ItemGroup>
    <ProjectReference Include="..\buildtool\buildtool.csproj" ExcludeAssets="all" Properties="RuntimeIdentifier=">
      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
      <CopyToOutputDirectory>Never</CopyToOutputDirectory>
      <CopyLocal>false</CopyLocal>
      <SkipGetTargetFrameworkProperties>true</SkipGetTargetFrameworkProperties>
      <ExcludeAssets>all</ExcludeAssets>
    </ProjectReference>
  </ItemGroup>

What's going on is I have a build tool in the solution, and dotnet publish is trying (incorrectly) to ship it. Almost minimized sample attached. If it were any smaller it wouldn't make any sense.
depbuildtool.zip

[teneko]

I can confirm that this behaviour is occuring, I have a synthetic project that only needs to be built but any

<None>
<CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
<!-- or -->
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</None>

is copied to projects with reference to synthetic project

<ProjectReference>
<ReferenceOutputAssembly>false</ReferenceOutputAssembly>
</ProjectReference>

[jhudsoncedaron]

Thanks to a random stackoverflow post, we now know that <Private>false</Private> works, but this isn't very sensible. It tells the compiler the assembly is in the GAC, which it isn't.

[teneko]

You made my day. Here the SO post for reference: https://stackoverflow.com/questions/26242937/what-does-the-private-setting-do-on-a-projectreference-in-a-msbuild-project-file. <Private>false</Private> can be applied to <ProjectReference />.

When you don't need any CopyTo[..]Directory functionality in synthetic project, an another workaround might be:

<Project>

  <Import Sdk="Microsoft.NET.Sdk" Project="Sdk.props" />

  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
    <!-- ... -->
  </PropertyGroup>

  <Import Sdk="Microsoft.NET.Sdk" Project="Sdk.targets" />

  <!--
  Overrides that return empty @(AllItemsFullPathWithTargetPath)
  -->

  <!-- https://github.com/dotnet/msbuild/blob/116af13e6760ebbb8466174201f1ebbc8df11dfa/src/Tasks/Microsoft.Common.CurrentVersion.targets#L4561 -->
  <Target Name="GetCopyToOutputDirectoryItems" />
  <!-- or -->
  <!--  https://github.com/dotnet/msbuild/blob/116af13e6760ebbb8466174201f1ebbc8df11dfa/src/Tasks/Microsoft.Common.CurrentVersion.targets#L4624 -->
  <Target Name="GetCopyToPublishDirectoryItems" />

</Project>

But I am not sure which further implications this workaround may have.

[teneko]

Hi, I want just to state, that <Private>false</Private> may not work when using <MSBuild Projects="$(MSBuildProjectFullPath)" Targets="Publish" Properties="$(_MSBuildProperties)" /> and project $(MSBuildProjectFullPath) have ProjectReferences that have <None><CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory></None>
. I've read the source code around https://github.com/dotnet/sdk/blob/master/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Publish.targets and found the solution. You need to define _GetChildProjectCopyToPublishDirectoryItems=false so a example would be: <MSBuild Projects="$(MSBuildProjectFullPath)" Targets="Publish" Properties="TargetFramework=$(TargetFramework);_GetChildProjectCopyToPublishDirectoryItems=false" />

[benvillalobos]

cc @dsplaisted for the nuget/CLI/SDK sync

[JanKrivanek]

Investigated with @rainersigwald:

tl;dr;: Strictly speaking ReferenceOutputAssembly is behaving as it should (preventing the output assembly to be referenced and pulled to output folder by referencing project). However it might feel unexpected when referencing application (OutputType=exe), as other supplementary files (deps.json, runtimeconfig.json and mainly <app>.exe) are still copied to output folder.

Workaround: Specifying <Private>false</Private> metadata on such ProjectReference will make sure that those additional files (including the exe) are not pulle to output folder of referencing project. Note that it will as well block copying of any other files as for example those defined as <None Include="my-config.cfg" CopyToOutputDirectory="PreserveNewest" />

---

Background: The netcore application produces the .dll assembly, and few supplementary files (e.g. the .exe which is actually a native shim calling into the managed .dll), those supplementary files are added as None item by the sdk _ComputeNETCoreBuildOutputFiles target. This then down the road causes the files to be added to the output folder, as None items are not excluded when the ReferenceOutputAssembly=true, as it (as the names implies) concerns only to output assembly.

Changing the behavior so that even the None items are excluded could break come other scenarios that currently work (keeping to copy items explicitly added by user).

Possible fix: So the possible way of fixing this is to define another metadata (e.g. something like BuildAfter or EnforceBuildPrecedenceOnly), that would only caused the referenced project to build prior the current project, but wouldn't cause any (direct nor transitive) flow of outputs nor items.

Conclusion:
Such a fix is questionable as it needs changes on users side and proper documentation as well - so it's similar to guiding users bit by this to use the Private metadata (despit it has above mentioned limitations - but such a usecase should be very niche).