Build fails with error CS8751: Internal error in the C# compiler

[alevincenzi]

Hello.
Building the solution from a clean project, after a checkout of the master branch, fails with these three errors in the test project:

1>------ Build started: Project: Moq, Configuration: Debug Any CPU ------
2>------ Build started: Project: Moq.Tests.FSharpTypes, Configuration: Debug Any CPU ------
2>Moq.Tests.FSharpTypes -> C:\DEV\moq4\tests\Moq.Tests.FSharpTypes\bin\Debug\net472\Moq.Tests.FSharpTypes.dll
2>Moq.Tests.FSharpTypes -> C:\DEV\moq4\tests\Moq.Tests.FSharpTypes\bin\Debug\netcoreapp2.2\Moq.Tests.FSharpTypes.dll
1>Moq -> C:\DEV\moq4\src\Moq\bin\Debug\net45\Moq.dll
1>Moq -> C:\DEV\moq4\src\Moq\bin\Debug\netstandard2.0\Moq.dll
3>------ Build started: Project: Moq.Tests, Configuration: Debug Any CPU ------
4>------ Build started: Project: Moq.Tests.VisualBasic, Configuration: Debug Any CPU ------
4>Moq.Tests.VisualBasic -> C:\DEV\moq4\tests\Moq.Tests.VisualBasic\bin\Debug\net472\Moq.Tests.VisualBasic.dll
3>C:\DEV\moq4\tests\Moq.Tests\ComCompatibilityFixture.cs(86,57,86,73): error CS8751: Internal error in the C# compiler.
3>C:\DEV\moq4\tests\Moq.Tests\ComCompatibilityFixture.cs(93,57,93,73): error CS8751: Internal error in the C# compiler.
3>C:\DEV\moq4\tests\Moq.Tests\ComCompatibilityFixture.cs(101,57,101,73): error CS8751: Internal error in the C# compiler.
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(31,16,31,29): warning CS0183: The given expression is always of the provided ('int?') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(39,16,39,31): warning CS0183: The given expression is always of the provided ('object') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(47,17,47,30): warning CS0184: The given expression is never of the provided ('long') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(55,17,55,29): warning CS0184: The given expression is never of the provided ('int') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(63,17,63,30): warning CS0184: The given expression is never of the provided ('uint') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(79,17,79,32): warning CS0184: The given expression is never of the provided ('int?[]') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(95,17,95,34): warning CS0184: The given expression is never of the provided ('object[]') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(103,17,103,32): warning CS0184: The given expression is never of the provided ('uint[]') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(119,16,119,36): warning CS0183: The given expression is always of the provided ('IComparable') type
3>C:\DEV\moq4\tests\Moq.Tests\Regressions\IssueReportsFixture.cs(2997,33,2997,34): warning CS0067: The event 'IssueReportsFixture.Issue893.A.E' is never used
3>Done building project "Moq.Tests.csproj" -- FAILED.
4>Moq.Tests.VisualBasic -> C:\DEV\moq4\tests\Moq.Tests.VisualBasic\bin\Debug\netcoreapp2.2\Moq.Tests.VisualBasic.dll
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(31,16,31,29): warning CS0183: The given expression is always of the provided ('int?') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(39,16,39,31): warning CS0183: The given expression is always of the provided ('object') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(47,17,47,30): warning CS0184: The given expression is never of the provided ('long') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(55,17,55,29): warning CS0184: The given expression is never of the provided ('int') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(63,17,63,30): warning CS0184: The given expression is never of the provided ('uint') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(79,17,79,32): warning CS0184: The given expression is never of the provided ('int?[]') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(95,17,95,34): warning CS0184: The given expression is never of the provided ('object[]') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(103,17,103,32): warning CS0184: The given expression is never of the provided ('uint[]') type
3>C:\DEV\moq4\tests\Moq.Tests\Matchers\IsAssignableFromVsIsOperatorFixture.cs(119,16,119,36): warning CS0183: The given expression is always of the provided ('IComparable') type
3>C:\DEV\moq4\tests\Moq.Tests\Regressions\IssueReportsFixture.cs(2997,33,2997,34): warning CS0067: The event 'IssueReportsFixture.Issue893.A.E' is never used
3>Moq.Tests -> C:\DEV\moq4\tests\Moq.Tests\bin\Debug\netcoreapp2.2\Moq.Tests.dll
3>Done building project "Moq.Tests.csproj".
========== Build: 3 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

In detail, the compiler errors show up in the usage of the interface IHasIndexer in these three lines:

var indexer = typeof(IHasIndexer).GetProperty(nameof(IHasIndexer.Item));

The interface resolves to: Moq.Tests.ComTypes.IHasIndexer but it gives the internal compiler error.

I run the build from:

Microsoft Visual Studio Community 2019
Version 16.5.3
VisualStudio.16.Release/16.5.3+30002.166
Microsoft .NET Framework
Version 4.8.03752

Installed Version: Community

Azure App Service Tools v3.0.0   16.5.236.49856
C# Tools   3.5.0-beta4-20153-05+20b9af913f1b8ce0a62f72bea9e75e4aa3cf6b0e
Common Azure Tools   1.10
IntelliCode Extension   1.0
Microsoft JVM Debugger   1.0
Microsoft MI-Based Debugger   1.0
NuGet Package Manager   5.5.0
ProjectServicesPackage Extension   1.0
Visual Basic Tools   3.5.0-beta4-20153-05+20b9af913f1b8ce0a62f72bea9e75e4aa3cf6b0e
Visual F# Tools 10.8.0.0 for F# 4.7   16.5.0-beta.20181.6+85af456066acd4e76d2bc7821b44a325e46f2fca
Microsoft Visual F# Tools 10.8.0.0 for F# 4.7
Visual Studio Code Debug Adapter Host Package   1.0

The dotnet --info from a console on my system (Windows 10) gives

.NET Core SDK (reflecting any global.json):
 Version:   3.1.201
 Commit:    b1768b4ae7

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18363
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.201\

Host (useful for support):
  Version: 3.1.3
  Commit:  4a9f85e9f8

.NET Core SDKs installed:
  2.1.805 [C:\Program Files\dotnet\sdk]
  3.1.201 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[stakx]

Hi @alevincenzi, thanks for reporting. I noticed the same thing just yesterday and reported this to the C# compiler team at dotnet/roslyn#43318... let's see what they say.

[alevincenzi]

Nice, @stakx . Thank you for the quick reply.
Any workaround to have my local copy build?

[stakx]

Any workaround to have my local copy build?

1. Comment out / remove the tests where the errors occur.
2. Unload / remove the whole test project.
3. Use Visual Studio 2017.

[alevincenzi]

Ok, sure, I meant except removing the tests.
Fine for me. Thanks.

[stakx]

@alevincenzi, I removed the problematic nameof instances. If you pull the latest commit on master, you should be able to compile now.