Can't serialize a ProjectId with a null DebugName

[KirillOsenkov]

Version Used:
https://dotnet.myget.org/feed/roslyn-for-vs-for-mac/package/nuget/Microsoft.CodeAnalysis.Workspaces.Common/2.7.0-vs-for-mac-62330-03

Steps to Reproduce:

MonoDevelop has a unit-test that crashes because the ProjectId has a null DebugName:
http://source.monodevelop.com/#MonoDevelop.CSharpBinding.Tests/MonoDevelop.CSharpBinding.Refactoring/CSharpFindReferencesProviderTests.cs,ced55906c09ac9c1

Expected Behavior:
Should be able to serialize a null string here:
https://github.com/dotnet/roslyn/blob/master/src/Workspaces/Core/Portable/Workspace/Solution/ProjectId.cs#L90

Actual Behavior:
Crash:

  at <unknown> <0xffffffff>
  at Roslyn.Utilities.ObjectWriter.WriteString (string) [0x00000] in /_/src/Compilers/Core/Portable/Serialization/ObjectWriter.cs:120
  at Microsoft.CodeAnalysis.ProjectId.Roslyn.Utilities.IObjectWritable.WriteTo (Roslyn.Utilities.ObjectWriter) [0x0000c] in /_/src/Workspaces/Core/Portable/Workspace/Solution/ProjectId.cs:90
  at Microsoft.CodeAnalysis.Shared.Extensions.SolutionExtensions.WriteTo (Roslyn.Utilities.IObjectWritable,Roslyn.Utilities.ObjectWriter) [0x00000] in /_/src/Workspaces/Core/Portable/Shared/Extensions/SolutionExtensions.cs:11
  at Microsoft.CodeAnalysis.ProjectInfo/ProjectAttributes.WriteTo (Roslyn.Utilities.ObjectWriter) [0x00000] in /_/src/Workspaces/Core/Portable/Workspace/Solution/ProjectInfo.cs:438
  at Microsoft.CodeAnalysis.Checksum.Create (Microsoft.CodeAnalysis.Serialization.WellKnownSynchronizationKind,Roslyn.Utilities.IObjectWritable) [0x0001d] in /_/src/Workspaces/Core/Portable/Workspace/Solution/Checksum_Factory.cs:55
  at Microsoft.CodeAnalysis.ProjectInfo/ProjectAttributes.Microsoft.CodeAnalysis.IChecksummedObject.get_Checksum () [0x0000e] in /_/src/Workspaces/Core/Portable/Workspace/Solution/ProjectInfo.cs:478
  at Microsoft.CodeAnalysis.Serialization.Serializer.CreateChecksum (object,System.Threading.CancellationToken) [0x00028] in /_/src/Workspaces/Core/Portable/Execution/Serializer.cs:61
  at Microsoft.CodeAnalysis.ProjectState/<ComputeChecksumsAsync>d__111.MoveNext () [0x000c0] in /_/src/Workspaces/Core/Portable/Workspace/Solution/ProjectState_Checksum.cs:41
  at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<Microsoft.CodeAnalysis.Serialization.ProjectStateChecksums>.Start<Microsoft.CodeAnalysis.ProjectState/<ComputeChecksumsAsync>d__111> (Microsoft.CodeAnalysis.ProjectState/<ComputeChecksumsAsync>d__111&) [0x0002c] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:471
  at Microsoft.CodeAnalysis.ProjectState.ComputeChecksumsAsync (System.Threading.CancellationToken) [0x0002f] in <04e532e269994a46ad655a7ff113b901>:0
  at Roslyn.Utilities.AsyncLazy`1<T_REF>.StartAsynchronousComputation (Roslyn.Utilities.AsyncLazy`1/AsynchronousComputationToStart<T_REF>,Roslyn.Utilities.AsyncLazy`1/Request<T_REF>,System.Threading.CancellationToken) [0x00013] in /_/src/Workspaces/Core/Portable/Utilities/AsyncLazy`1.cs:388
  at Roslyn.Utilities.AsyncLazy`1<T_REF>.GetValueAsync (System.Threading.CancellationToken) [0x00085] in /_/src/Workspaces/Core/Portable/Utilities/AsyncLazy`1.cs:344
  at Microsoft.CodeAnalysis.ProjectState.GetStateChecksumsAsync (System.Threading.CancellationToken) [0x00000] in /_/src/Workspaces/Core/Portable/Workspace/Solution/ProjectState_Checksum.cs:21
  at Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetChecksumAsync>d__55.MoveNext () [0x00011] in /_/src/Workspaces/Core/Portable/FindSymbols/SyntaxTree/SyntaxTreeIndex_Persistence.cs:83
  at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<Microsoft.CodeAnalysis.Checksum>.Start<Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetChecksumAsync>d__55> (Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetChecksumAsync>d__55&) [0x0002c] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:471
  at Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex.GetChecksumAsync (Microsoft.CodeAnalysis.Document,System.Threading.CancellationToken) [0x0002f] in <04e532e269994a46ad655a7ff113b901>:0
  at Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetIndexWorkerAsync>d__10.MoveNext () [0x0001d] in /_/src/Workspaces/Core/Portable/FindSymbols/SyntaxTree/SyntaxTreeIndex.cs:75
  at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex>.Start<Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetIndexWorkerAsync>d__10> (Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetIndexWorkerAsync>d__10&) [0x0002c] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:471
  at Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex.GetIndexWorkerAsync (Microsoft.CodeAnalysis.Document,System.Threading.CancellationToken) [0x0002f] in <04e532e269994a46ad655a7ff113b901>:0
  at Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetIndexAsync>d__9.MoveNext () [0x00035] in /_/src/Workspaces/Core/Portable/FindSymbols/SyntaxTree/SyntaxTreeIndex.cs:61
  at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex>.Start<Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetIndexAsync>d__9> (Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex/<GetIndexAsync>d__9&) [0x0002c] in /Users/builder/data/lanes/5533/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:471
  at Microsoft.CodeAnalysis.FindSymbols.SyntaxTreeIndex.GetIndexAsync (Microsoft.CodeAnalysis.Document,System.Threading.CancellationToken) [0x0002f] in <04e532e269994a46ad655a7ff113b901>:0```

[KirillOsenkov]

Note: this is unconfirmed. We suspect that this could be a Mono runtime issue. It is unclear whether it's an actual issue in Roslyn too and they overlap or if Roslyn is not at fault. I will update this issue when we know more.

Mono runtime fix:
mono/mono@ddeba6e

Native stack:

Native stacktrace:

    0   libmonosgen-2.0.dylib               0x00000001032bc201 mono_handle_native_crash + 257
    1   libmonosgen-2.0.dylib               0x0000000103325586 altstack_handle_and_restore + 70
    2   libmonosgen-2.0.dylib               0x000000010327ad27 mono_local_cprop + 423
    3   libmonosgen-2.0.dylib               0x0000000103207a78 mini_method_compile + 4456
    4   libmonosgen-2.0.dylib               0x000000010320acd6 mono_jit_compile_method_inner + 790
    5   libmonosgen-2.0.dylib               0x000000010320e223 mono_jit_compile_method_with_opt + 1363
    6   libmonosgen-2.0.dylib               0x00000001032be6c1 common_call_trampoline + 1217
    7   libmonosgen-2.0.dylib               0x00000001032be1bc mono_magic_trampoline + 60```

[KirillOsenkov]

We have now confirmed that this was a Mono runtime issue, fixed with mono/mono@ddeba6e.

Roslyn behaves as designed. Closing.

/cc @jasonmalinowski

[KirillOsenkov]

You need Mono >= 5.8.0.130 to avoid hitting this issue.