[10.0.1xx-rc2] AspNetCore Build Failure due to Analyzer Compiler Version Mismatch

[ellahathaway]

Link to failing build

AspNetCore is failing to build in the public and internal 10.0 RC2 branches due to a compiler version mismatch. The error encountered is:

CSC : error CS9057: Analyzer assembly '/__w/1/s/src/aspnetcore/artifacts/bin/Microsoft.AspNetCore.Http.RequestDelegateGenerator/Release/netstandard2.0/Microsoft.AspNetCore.Http.RequestDelegateGenerator.dll' cannot be used because it references version '5.1.0.0' of the compiler, which is newer than the currently running version '5.0.0.0'. [/__w/1/s/src/aspnetcore/src/Identity/Core/src/Microsoft.AspNetCore.Identity.csproj]

[mthalman]

I don't know if the warning is the cause of the failure. I see this error as well:

CSC : error CS9057: Analyzer assembly '/__w/1/s/src/aspnetcore/artifacts/bin/Microsoft.AspNetCore.Http.RequestDelegateGenerator/Release/netstandard2.0/Microsoft.AspNetCore.Http.RequestDelegateGenerator.dll' cannot be used because it references version '5.1.0.0' of the compiler, which is newer than the currently running version '5.0.0.0'. [/__w/1/s/src/aspnetcore/src/Identity/Core/src/Microsoft.AspNetCore.Identity.csproj]

[MichaelSimons]

The aspnetcore.log indicates the following error:

CSC : error CS9057: Analyzer assembly '/__w/1/s/src/aspnetcore/artifacts/bin/Microsoft.AspNetCore.Http.RequestDelegateGenerator/Release/netstandard2.0/Microsoft.AspNetCore.Http.RequestDelegateGenerator.dll' cannot be used because it references version '5.1.0.0' of the compiler, which is newer than the currently running version '5.0.0.0'. [/__w/1/s/src/aspnetcore/src/Identity/Core/src/Microsoft.AspNetCore.Identity.csproj]
    0 Warning(s)
    1 Error(s)

That smells like a bootstrapping issue - we do not allow re-bootstrapping once we are in RC mode. @wtgodbe

[ellahathaway]

Thanks! I've updated the issue title and body to reflect the actual error.

[wtgodbe]

This is due to an incorrect flow from Roslyn main, bumping the version there to 5.1. dotnet/dotnet#2598 should fix

[ellahathaway]

Confirmed that dotnet/dotnet#2598 fixed this issue: https://dev.azure.com/dnceng/internal/_build/results?buildId=2801001&view=results.