API-using application is spawned instead of `dotnet` when using CodeTaskFactory

[Leon99]

I'm trying to open csproj files via Microsoft.CodeAnalysis.MSBuild.MSBuildWorkspace.OpenProjectAsync from my console app. One of the projects, a rather big one, hangs the execution and spawns another instance of the app.

Tried both v4.6.0 from nuget.org and built myself from https://github.com/dotnet/roslyn/releases/tag/Visual-Studio-2022-Version-17.6.4, same behavior.

Tried to debug but quickly got lost... My best guess is that MSBuild is trying to create additional processes (for compilation?) to parallelize since it's a large project, but instead instantiates my app.
Any suggestions much appreciated.

[Leon99]

Here's a screenshot from Task Manager that shows the command line:

[Leon99]

Same behavior with 4.6.0 from nuget.org

[jasonmalinowski]

Under the covers OpenProjectAsync triggers a build of your project via MSBuild, but in a way that is supposed to prevent the compiler actually running. Did you customize your build in some way so the build of a project also runs it?

[Leon99]

Thanks for the idea, @jasonmalinowski!
I localized the issue to this fragment in the csproj:

 <UsingTask TaskName="WaitForFiles" TaskFactory="RoslynCodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
    <ParameterGroup>
      <Files ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="true" />
    </ParameterGroup>
    <Task>
      <Using Namespace="System.IO" />
      <Using Namespace="System.Linq" />
      <Code Type="Fragment" Language="cs"><![CDATA[
			Files.AsParallel().ForAll(
                file =>
                {
                    var fileName = file.ItemSpec.ToString();
                    var startTime = DateTime.UtcNow;
                    while (true)
                    {
                        try
                        {
                            using (var fs = new FileStream(fileName, FileMode.Open, FileAccess.ReadWrite, FileShare.Read))
                            {
                                if (fs.Length > 0)
                                {
                                    Log.LogMessage(MessageImportance.High, $"File {fileName} is available!");
                                    return;
                                }
                            }
                        }
                        catch
                        {
                            // ignore
                        }
            
                        if ((DateTime.UtcNow - startTime).TotalSeconds > 10)
                        {
                            Log.LogWarning($"File {fileName} is still locked by another process... Stop waiting and give up.");
                            return;
                        }

                        Log.LogWarning($"File {fileName} is still locked by another process...");
                        System.Threading.Thread.Sleep(1000);
                    }
                });
      ]]></Code>
    </Task>
  </UsingTask>
  <Target Name="WaitForAllFilesBeforeCompile" BeforeTargets="CoreCompile">
    <Message Importance="High" Text="$(MSBuildProjectName): WaitForAllFilesBeforeCompile" />
    <WaitForFiles Files="@(Compile)" />
    <Message Importance="High" Text="$(MSBuildProjectName): /WaitForAllFilesBeforeCompile" />
  </Target>

[jasonmalinowski]

Ah, the use of RoslynCodeTaskFactory might be the problem here. Can you share the full command line of one of the processes that was being launched? You can of course redact user names, company/product names, but in this case it's important to see the source files being compiled and what the switches are being passed.

[Leon99]

1st process:

Worker.dll "C:\Program Files\dotnet\sdk\7.0.304\Roslyn\bincore\csc.dll" /noconfig "/reference:C:\Program Files\dotnet\sdk\7.0.304\ref\Microsoft.Build.Framework.dll" "/reference:C:\Program Files\dotnet\sdk\7.0.304\ref\Microsoft.Build.Utilities.Core.dll" "/reference:C:\Program Files\dotnet\sdk\7.0.304\ref\mscorlib.dll" "/reference:C:\Program Files\dotnet\sdk\7.0.304\ref\netstandard.dll" /deterministic+ /nologo /optimize- /target:Library /out:C:\Users\leonv\AppData\Local\Temp\MSBuildTempleonv\tmp96be05b9ef394598bc9b849aa6d5512d.dll C:\Users\leonv\AppData\Local\Temp\MSBuildTempleonv\tmp0381fc715c144e29a4435dbc6ecdcd39.tmp /nostdlib+

2nd and following:

Worker.dll "C:\Program Files\dotnet\sdk\6.0.315\Roslyn\bincore\csc.dll" /noconfig "/reference:C:\Program Files\dotnet\sdk\6.0.315\ref\Microsoft.Build.Framework.dll" "/reference:C:\Program Files\dotnet\sdk\6.0.315\ref\Microsoft.Build.Utilities.Core.dll" "/reference:C:\Program Files\dotnet\sdk\6.0.315\ref\mscorlib.dll" "/reference:C:\Program Files\dotnet\sdk\6.0.315\ref\netstandard.dll" /deterministic+ /nologo /optimize- /target:Library /out:C:\Users\leonv\AppData\Local\Temp\MSBuildTempleonv\tmpa1950816718744f5892bf6b98744c38f.dll C:\Users\leonv\AppData\Local\Temp\MSBuildTempleonv\tmp0f3b558462e844dea3bd6774fb234fea.tmp /nostdlib+

[rainersigwald]

@Leon99 can you tell us more about your application--are you building it self-contained or single-file? are you running it with application.exe or dotnet application.dll?

If you're using application.exe can you please try running application.dll? I suspect that would work around the issue.

Background: RoslynCodetaskFactory invokes dotnet csc.dll to build the temporary task assembly. But what dotnet should it run? We try to run "the same one we're running in" . . . but it looks like we might be getting that wrong in your case and running yourapplication.exe instead of dotnet.exe.