Use apphost for core compiler

[jjonescz]

The trick is to set DOTNET_ROOT based on the DOTNET_HOST_PATH which we already have available. Then csc.exe/vbc.exe/VBCSCompiler.exe should behave just like the dotnet exec *.dll equivalent behaved previously. Plus there are benefits - quoting @jaredpar: with this we get named processes back and all the benefits that come with it: better perf bucketing, Watson, kill VBCSCompiler.exe keeps working, etc.

Part of dotnet/msbuild#11142.

[jaredpar]

Why are you going this approach vs. just customizing the environment variables in the process start info? MSBuild is looking hard into single process execution in the future, this would be a code path we'd have to come back and revisit if that happened as they'd ban global env changing.

[jjonescz]

Because the Windows code path uses P/Invoke and customizing the environment variables there seems non-trivial.

[jaredpar]

Let's take a follow up item to fix that post .NET 10 RTM

[jjonescz]

I've investigated more and seems the problem is the "inherit handles" flag which is hardcoded to true in the runtime whereas we need false there otherwise the Csc task just hangs (waiting for the spawned VBCSCompiler process to exit I guess?)

Anyway, opened #80079.

[jaredpar]

Pretty sure @agocke dug into the inherits handle flag at one point. He might have context here.

[jjonescz]

The tests failing in some CI legs reveal possible regressions if we take this change:

1. The single machine Linux leg fails due to missing .NET 9 runtime. I'm not sure why dotnet csc.dll didn't fail and DOTNET_ROOT=... csc fails, perhaps I'm doing something wrong here.

Logs

CoreCompile:
          /mnt/vss/_work/1/s/artifacts/bin/Microsoft.Build.Tasks.CodeAnalysis.UnitTests/Debug/net9.0/bincore/csc /noconfig /unsafe- /checked- /nowarn:1701,1702,1701,1702 /fullpaths /nostdlib+ /errorreport:prompt /define:TRACE;DEBUG;NETSTANDARD;NETSTANDARD2_0;NETSTANDARD1_0_OR_GREATER;NETSTANDARD1_1_OR_GREATER;NETSTANDARD1_2_OR_GREATER;NETSTANDARD1_3_OR_GREATER;NETSTANDARD1_4_OR_GREATER;NETSTANDARD1_5_OR_GREATER;NETSTANDARD1_6_OR_GREATER;NETSTANDARD2_0_OR_GREATER /highentropyva+ /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/Microsoft.Win32.Primitives.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/mscorlib.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/netstandard.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.AppContext.dll 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/reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Resources.Reader.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Resources.ResourceManager.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Resources.Writer.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.CompilerServices.VisualC.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Extensions.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Handles.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.InteropServices.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.InteropServices.RuntimeInformation.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Numerics.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Serialization.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Serialization.Formatters.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Serialization.Json.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Serialization.Primitives.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Runtime.Serialization.Xml.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Claims.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Cryptography.Algorithms.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Cryptography.Csp.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Cryptography.Encoding.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Cryptography.Primitives.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Cryptography.X509Certificates.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.Principal.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Security.SecureString.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.ServiceModel.Web.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Text.Encoding.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Text.Encoding.Extensions.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Text.RegularExpressions.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.Overlapped.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.Tasks.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.Tasks.Parallel.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.Thread.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.ThreadPool.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Threading.Timer.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Transactions.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.ValueTuple.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Web.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Windows.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.Linq.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.ReaderWriter.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.Serialization.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.XDocument.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.XmlDocument.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.XmlSerializer.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.XPath.dll /reference:/home/cloudtest/.nuget/packages/netstandard.library/2.0.3/build/netstandard2.0/ref/System.Xml.XPath.XDocument.dll /debug+ /debug:portable /filealign:512 /optimize- /out:obj/Debug/netstandard2.0/Test.dll /target:library /warnaserror- /utf8output /deterministic+ /langversion:7.3 /analyzerconfig:obj/Debug/netstandard2.0/Test.GeneratedMSBuildEditorConfig.editorconfig File.cs "obj/Debug/netstandard2.0/.NETStandard,Version=v2.0.AssemblyAttributes.cs" obj/Debug/netstandard2.0/Test.AssemblyInfo.cs /warnaserror+:NU1605
          Setting DOTNET_ROOT to '/mnt/vss/_work/1/s/.dotnet'
          Compilation request Test (netstandard2.0), PathToTool=/mnt/vss/_work/1/s/artifacts/bin/Microsoft.Build.Tasks.CodeAnalysis.UnitTests/Debug/net9.0/bincore/csc
          CompilerServer: tool - using command line tool by design '/mnt/vss/_work/1/s/artifacts/bin/Microsoft.Build.Tasks.CodeAnalysis.UnitTests/Debug/net9.0/bincore/csc' - Test (netstandard2.0)
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : You must install or update .NET to run this application. [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :  [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : App: /mnt/vss/_work/1/s/artifacts/bin/Microsoft.Build.Tasks.CodeAnalysis.UnitTests/Debug/net9.0/bincore/csc [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : Architecture: x64 [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : Framework: 'Microsoft.NETCore.App', version '9.0.0' (x64) [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : .NET location: /usr/lib/dotnet [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :  [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : The following frameworks were found: [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :   6.0.36 at [/usr/lib/dotnet/shared/Microsoft.NETCore.App] [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :  [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : Learn about framework resolution: [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : https://aka.ms/dotnet/app-launch-failed [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :  [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : To install missing framework, download: [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>/mnt/vss/_work/1/s/.dotnet/sdk/10.0.100-preview.6.25358.103/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : https://aka.ms/dotnet-core-applaunch?framework=Microsoft.NETCore.App&framework_version=9.0.0&arch=x64&rid=ubuntu.22.04-x64 [/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj]
      1>Done Building Project "/tmp/RoslynTests/aef9b98c-4f0e-4855-a96a-ea07f646f61e/Test.csproj" (Build target(s)) -- FAILED.

2. If the executables are copied without chmod +x, they will fail to start. That was happening in our CI as well until I changed the rehydration utility (see changes in src/Tools/PrepareTests/MinimizeUtil.cs).
3. When the Csc task is built on Linux and executed on macOS, previously that worked fine, now it fails with "Exec format error". I guess that's because the macOS runs on ARM so needs a different apphost which makes sense, but someone could be relying on this behavior (like our CI currently is!)

@jaredpar are those breaks acceptable?

[jaredpar]

I'm fine with both (2) and (3). The rational is that this is how the .NET SDK generally works today for any other component hence we're just falling in line with that behavior.

The single machine Linux leg fails due to missing .NET 9 runtime. I'm not sure why dotnet csc.dll didn't fail and DOTNET_ROOT=... csc fails, perhaps I'm doing something wrong here.

That is odd. Not sure why an apphost would bake in a stronger .NET runtime requirement than the dotnet exec approach. @jkoritzinsky, @agocke any thoughts on why this would happen?

[agocke]

Best guess is something in the runtimeconfig.json changed (or the file appeared for the first time). Can you see what it says inside? If you want to run on net8+ it should be net8 with roll forward major.

[jjonescz]

The file is the same before and after.

{
  "runtimeOptions": {
    "tfm": "net9.0",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "9.0.0"
    },
    "rollForward": "Major",
    "configProperties": {
      "System.GC.Server": true,
      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
    }
  }
}

[jjonescz]

Just realized only csc/vbc fails, VBCSCompiler seems to work fine, so I guess there is really something different in the way we launch them, will investigate more...

[agocke]

Maybe enum values are parsed case-insensitive, but I notice on https://learn.microsoft.com/en-us/dotnet/core/tools/global-json#rollforward that the casing is lower case, i.e. rollForward": "major". Might be worth changing that just in case this is working by accident.

[jjonescz]

I think I'm just setting DOTNET_ROOT incorrectly when invoking csc/vbc, will fix.

Regarding casing, I believe the runtimeconfig.json file is generated by the build...

[agocke]

You're right, it's flowed in through MSBuild using different casing: https://learn.microsoft.com/en-us/dotnet/core/project-sdk/msbuild-props#rollforward

This must be case-insensitive and undocumented.

[agocke]

Also, just saw this part:

When the Csc task is built on Linux and executed on macOS, previously that worked fine, now it fails with "Exec format error". I guess that's because the macOS runs on ARM so needs a different apphost which makes sense, but someone could be relying on this behavior (like our CI currently is!)

Right, the apphost is a native binary so it needs to match the platform you're building for. Meaning you'll need a different package for each target platform.

[jaredpar]

@RikkiGibson, @JoeRobich PTAL

[JoeRobich]

Can you document this?