Microsoft.Cci.PdbWriter.GetAssemblyReferenceAlias throws Null Reference exception

[WindingWinter]

This happens with VS 2022 ( 17.11.1 version).

I have a solution, that will throw me Null Reference Exception because I'm using Global Usings. Here's the stack trace:

13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error : Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.PdbWriter.GetAssemblyReferenceAlias(IAssemblyReference assembly, HashSet`1 declaredExternAliases)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.PdbWriter.TryEncodeImport(UsedNamespaceOrType import, HashSet`1 declaredExternAliasesOpt, Boolean isProjectLevel)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.PdbWriter.DefineNamespaceScopes(IMethodBody methodBody)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.PdbWriter.SerializeDebugInfo(IMethodBody methodBody, StandaloneSignatureHandle localSignatureHandleOpt, CustomDebugInfoWriter customDebugInfoWriter)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.MetadataWriter.SerializeMethodBodies(BlobBuilder ilBuilder, PdbWriter nativePdbWriterOpt, Blob& mvidStringFixup)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.MetadataWriter.BuildMetadataAndIL(PdbWriter nativePdbWriterOpt, BlobBuilder ilBuilder, PooledBlobBuilder& mappedFieldDataBuilder, PooledBlobBuilder& managedResourceDataBuilder, Blob& mvidFixup, Blob& mvidStringFixup)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.Cci.PeWriter.WritePeToStream(EmitContext context, CommonMessageProvider messageProvider, Func`1 getPeStream, Func`1 getPortablePdbStreamOpt, PdbWriter nativePdbWriterOpt, String pdbPathOpt, Boolean metadataOnly, Boolean isDeterministic, Boolean emitTestCoverageData, Nullable`1 privateKeyOpt, CancellationToken cancellationToken)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.Compilation.SerializePeToStream(CommonPEModuleBuilder moduleBeingBuilt, DiagnosticBag metadataDiagnostics, CommonMessageProvider messageProvider, Func`1 getPeStream, Func`1 getMetadataPeStreamOpt, Func`1 getPortablePdbStreamOpt, PdbWriter nativePdbWriterOpt, String pdbPathOpt, RebuildData rebuildData, Boolean metadataOnly, Boolean includePrivateMembers, Boolean isDeterministic, Boolean emitTestCoverageData, Nullable`1 privateKeyOpt, CancellationToken cancellationToken)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.Compilation.SerializeToPeStream(CommonPEModuleBuilder moduleBeingBuilt, EmitStreamProvider peStreamProvider, EmitStreamProvider metadataPEStreamProvider, EmitStreamProvider pdbStreamProvider, RebuildData rebuildData, Func`2 testSymWriterFactory, DiagnosticBag diagnostics, EmitOptions emitOptions, Nullable`1 privateKeyOpt, CancellationToken cancellationToken)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommonCompiler.CompileAndEmit(TouchedFileLogger touchedFilesLogger, Compilation& compilation, ImmutableArray`1 analyzers, ImmutableArray`1 generators, ImmutableArray`1 additionalTextFiles, AnalyzerConfigSet analyzerConfigSet, ImmutableArray`1 sourceFileAnalyzerConfigOptions, ImmutableArray`1 embeddedTexts, DiagnosticBag diagnostics, ErrorLogger errorLogger, CancellationToken cancellationToken, CancellationTokenSource& analyzerCts, AnalyzerDriver& analyzerDriver, Nullable`1& generatorTimingInfo)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommonCompiler.RunCore(TextWriter consoleOutput, ErrorLogger errorLogger, CancellationToken cancellationToken)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommonCompiler.Run(TextWriter consoleOutput, CancellationToken cancellationToken)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Csc.<>c__DisplayClass1_0.<Run>b__0(TextWriter tw)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommandLine.ConsoleUtil.RunWithUtf8Output[T](Func`2 func)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Csc.Run(String[] args, BuildPaths buildPaths, TextWriter textWriter, IAnalyzerAssemblyLoader analyzerLoader)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommandLine.BuildClient.RunLocalCompilation(String[] arguments, BuildPaths buildPaths, TextWriter textWriter)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommandLine.BuildClient.RunCompilation(IEnumerable`1 originalArguments, BuildPaths buildPaths, TextWriter textWriter, String pipeName)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CommandLine.BuildClient.Run(IEnumerable`1 arguments, RequestLanguage language, CompileFunc compileFunc, CompileOnServerFunc compileOnServerFunc, ICompilerServerLogger logger)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Program.MainCore(String[] args)
13>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets(85,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Program.Main(String[] args)

The workaround that I can have is that I stop using global usings. Eg: I remove the GlobalUsings.cs file that contains the following two lines of code

extern alias Data;
global using Data::XXX.YYY.Data;

And the problem goes away.

But the problem is that when I try to create a scale down project, I can't reproduce the error. I thought it's a simple case of using extern alias with global using, but I was wrong.

I am pretty sure that this is a bug from Rosyln compiler. Any idea how to reproduce an actionable bug report?

[jjonescz]

Instead of creating a minimal example, you could create a complog and send it to us for investigation. Note that it will contain all inputs, but you can send it privately via VS feedback (just link the ticket here then).

[WindingWinter]

@jjonescz . here's the VS feedback link

[AlekseyTs]

https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2225493

[AlekseyTs]

        [WorkItem("https://github.com/dotnet/roslyn/issues/74872")]
        [Fact]
        public void ExternAliases6()
        {
            string sourceA =
@"
namespace N
{
    public class A { }
}
";
            var comp = CreateCompilation(sourceA, assemblyName: "A1");
            var refA = comp.EmitToImageReference(aliases: ImmutableArray.Create("A2"));

            string sourceB =
@"
class B
{
    static void F(A x) { }
}
";
            string sourceC =
@"
extern alias A2;
global using A2::N;
";
            comp = CreateCompilation([sourceB, sourceC], references: new[] { refA }, options: TestOptions.DebugDll);
            comp.VerifyDiagnostics();
            comp.VerifyPdb(
@"
<symbols>
  <files>
    <file id=""1"" name="""" language=""C#"" />
  </files>
  <methods>
    <method containingType=""B"" name=""F"" parameterNames=""x"">
      <customDebugInfo>
        <using>
          <namespace usingCount=""1"" />
        </using>
      </customDebugInfo>
      <sequencePoints>
        <entry offset=""0x0"" startLine=""4"" startColumn=""24"" endLine=""4"" endColumn=""25"" document=""1"" />
        <entry offset=""0x1"" startLine=""4"" startColumn=""26"" endLine=""4"" endColumn=""27"" document=""1"" />
      </sequencePoints>
      <scope startOffset=""0x0"" endOffset=""0x2"">
        <namespace qualifier=""A2"" name=""N"" />
        <externinfo alias=""A2"" assembly=""A1, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"" />
      </scope>
    </method>
  </methods>
</symbols>
");
        }

        [WorkItem("https://github.com/dotnet/roslyn/issues/74872")]
        [Fact]
        public void ExternAliases7()
        {
            string sourceA =
@"
namespace N
{
    public class A { }
}
";
            var comp = CreateCompilation(sourceA, assemblyName: "A1");
            var refA = comp.EmitToImageReference(aliases: ImmutableArray.Create("A2"));

            string sourceB =
@"
class B
{
    static void F(N2.A x) { }
}
";
            string sourceC =
@"
extern alias A2;
global using N2 = A2::N;
";
            comp = CreateCompilation([sourceB, sourceC], references: new[] { refA }, options: TestOptions.DebugDll);
            comp.VerifyDiagnostics();
            comp.VerifyPdb(
@"
<symbols>
  <files>
    <file id=""1"" name="""" language=""C#"" />
  </files>
  <methods>
    <method containingType=""B"" name=""F"" parameterNames=""x"">
      <customDebugInfo>
        <using>
          <namespace usingCount=""1"" />
        </using>
      </customDebugInfo>
      <sequencePoints>
        <entry offset=""0x0"" startLine=""4"" startColumn=""27"" endLine=""4"" endColumn=""28"" document=""1"" />
        <entry offset=""0x1"" startLine=""4"" startColumn=""29"" endLine=""4"" endColumn=""30"" document=""1"" />
      </sequencePoints>
      <scope startOffset=""0x0"" endOffset=""0x2"">
        <alias name=""N2"" qualifier=""A2"" target=""N"" kind=""namespace"" />
        <externinfo alias=""A2"" assembly=""A1, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"" />
      </scope>
    </method>
  </methods>
</symbols>
");
        }

[AlekseyTs]

@tmat Could you please advise what import information should be emitted for the scenarios above? Note that PdbValidation.VerifyPdb helper doesn't like references to undefined aliases: "PDB0007: token 0x35000002: An extern alias was not defined for assembly reference 23000002". At the same time it feels like defining an alias used by a global using would be incorrect because it is not in "scope" within sourceB.

[tmat]

Interesting corner case. I need to dig deeper into the code that reports the error.