Performance Regression: Build takes 7s in .net9 and 5min in .net10

[marklam]

https://github.com/marklam/SlowBuildRepro
Build is fine with global.json selecting .net 9, very slow when using .net 10

Known workarounds

Select .net 9 SDK

Related information

• Windows 11
• .net 10
• Visual Studio 18 Insiders

[majocha]

I can confirm this was fast even with rc sdk 10.0.100.

Upgrading to 10.0.101 - build takes forever.

Using the fsc.dll from main, it's fast again:

❯ dotnet build -c Release -p:DotnetFscCompilerPath=D:\source\fsharp\artifacts\bin\fsc\Release\net10.0\fsc.dll -bl --no-incremental
Restore complete (0.4s)
  SlowBuild net9.0 succeeded (8.0s) → SlowBuild\bin\Release\net9.0\SlowBuild.dll

Build succeeded in 8.7s

I think this is already fixed as of latest changes in main.

Removing
<FSharpPreferNetFrameworkTools>False</FSharpPreferNetFrameworkTools>

made it fast for me also when building in the IDE. I guess this option forces VS to use the released SDK 10.0.101 which has the unfortunate bug. and without it, msbuild uses the vsix provided one.

[T-Gro]

FSharpPreferNetFrameworkTools = true (also the default in VS) ===> uses the net472 build of the compiler, shipped with VS and runs on the desktop .NET Framework.

FSharpPreferNetFrameworkTools = false (the default in the SDK) ===> uses the net10 build of the compiler, shipped with .NET SDK

At time likes the one we are at, the exact timing of the two platforms (release cadence SDK vs VS) can be different, even though they are sourced from the same F# code.

[majocha]

FSharpPreferNetFrameworkTools = true (also the default in VS) ===> uses the net472 build of the compiler, shipped with VS and runs on the desktop .NET Framework.

Stupid question but does F# net472 compiler actually ship with VisualFSharp vsix or separately as part of VS?

[T-Gro]

Is what you have after installation at (e.g.): C:\Program Files\Microsoft Visual Studio\18\Insiders\Common7\IDE\CommonExtensions\Microsoft\FSharp\Tools

https://github.com/dotnet/fsharp/blob/main/vsintegration/Vsix/VisualFSharpFull/Source.extension.vsixmanifest

It should all be part of the same .vsix with all other tools

[T-Gro]

But if you install an override via a custom built .vsix, I am afraid it will not replace the built-in ones and F# .props and .targets will still refer the built in one.
For the same reason why it was not used for F5 on VisualFSharpDebug and it needed env var overrides to point to the local one.

[marklam]

Without the <FSharpPreferNetFrameworkTools>False</FSharpPreferNetFrameworkTools> and with a custom vsix, it builds quickly in Visual Studio Insiders.

But it still takes a long time from dotnet build.

Without a custom vsix, in Visual Studio GA it may well take a lifetime.