C# 14 Preview 3 massive errors for nested functional extensions

[tomschrot]

C# 14 Preview 3 massive errors for nested functional extensions:
(Linux Mint 22.1, VS Code 1.99.2)

Playing around with extensions, I get tons of errors for:

Program:

var sb =
        new StringBuilder("Info: ")
            .Snip    ( 1 )
            .Inspect ( c => Console.Write(c) );

Extension:
it compiles but will crash removing the foreach - comments below?!

namespace Extensions;

#nullable enable

public static class Test
{
    extension (StringBuilder sb)
    {
        //-------------------------------------------------------------------------

        public StringBuilder Snip (int n = 1)
        {
            var pos = sb.Length - int.Abs (n);

            if ( pos > 0 )
                sb.Remove (pos, n);

            return sb;
        }
        //-------------------------------------------------------------------------

        public StringBuilder Call (Action onCall)
        {
            onCall?.Invoke();
            return sb;
        }
        //-------------------------------------------------------------------------

        public StringBuilder Inspect (Action<char> onChar)
            =>
                sb.Call ( () =>
                {
                    // foreach (char c in sb.ToString())
                    //     onChar(c);
                });

        //-------------------------------------------------------------------------
    }
}
#nullable restore

    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error : Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.Cci.MetadataWriter.CheckNameLength(String name, INamedEntity errorEntity)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.Cci.MetadataWriter.PopulateFieldTableRows()
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.Cci.MetadataWriter.PopulateTypeSystemTables(Int32[] methodBodyOffsets, PooledBlobBuilder& mappedFieldDataWriter, PooledBlobBuilder& resourceWriter, BlobBuilder dynamicAnalysisData, Blob& mvidFixup)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.Cci.MetadataWriter.BuildMetadataAndIL(PdbWriter nativePdbWriterOpt, BlobBuilder ilBuilder, PooledBlobBuilder& mappedFieldDataBuilder, PooledBlobBuilder& managedResourceDataBuilder, Blob& mvidFixup, Blob& mvidStringFixup)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): 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)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): 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)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): 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)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): 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)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CommonCompiler.RunCore(TextWriter consoleOutput, ErrorLogger errorLogger, CancellationToken cancellationToken)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CommonCompiler.Run(TextWriter consoleOutput, CancellationToken cancellationToken)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Csc.Run(String[] args, BuildPaths buildPaths, TextWriter textWriter, IAnalyzerAssemblyLoader analyzerLoader)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CommandLine.BuildClient.RunCompilation(IEnumerable`1 originalArguments, BuildPaths buildPaths, TextWriter textWriter, String pipeName)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CommandLine.BuildClient.Run(IEnumerable`1 arguments, RequestLanguage language, CompileFunc compileFunc, CompileOnServerFunc compileOnServerFunc, ICompilerServerLogger logger)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Program.MainCore(String[] args)
    /home/user/.dotnet/sdk/10.0.100-preview.3.25201.16/Roslyn/Microsoft.CSharp.Core.targets(84,5): error :    at Microsoft.CodeAnalysis.CSharp.CommandLine.Program.Main(String[] args)

Erstellen von fehlerhaft mit 16 Fehler(n) in 6,9s

[bernd5]

A debug assert is triggered here:

roslyn/src/Compilers/CSharp/Portable/Lowering/ClosureConversion/LambdaCapturedVariable.cs

Line 112 in e3f3ac9

Debug.Assert(variable.Name != null);

Why are the ForEachArrayIndex und ForEachArray symbols considered as captured - in my eyes these should be simple locals - no fields...

The issue occurs only with the new extensions.

This code fails:

using System;
using System.Text;

var sb = new StringBuilder("Info: ");
Test.Inspect(sb);

public static class Test
{
    extension(StringBuilder)
    {
        public static StringBuilder Inspect(StringBuilder sb)
        {
            var s = () =>
            {
                foreach (char c in sb.ToString())
                {
                    Console.Write(c);
                }
            };
            s();
            return sb;
        }
    }    
}

And this works:

using System;
using System.Text;

var sb = new StringBuilder("Info: ");
Test.Inspect(sb);

public static class Test
{
    public static StringBuilder Inspect(StringBuilder sb)
    {
        var s = () =>
        {
            foreach (char c in sb.ToString())
            {
                Console.Write(c);
            }
        };
        s();
        return sb;
    }
}

[tomschrot]

It also works with the old extension syntax...

[bernd5]

The root of the issue is here:

roslyn/src/Compilers/CSharp/Portable/Lowering/ClosureConversion/ClosureConversion.Analysis.Tree.cs

Line 633 in 959bcb7

if (symbol.ContainingSymbol != _currentFunction.OriginalMethodSymbol)

There we compare a SourceExtensionImplementationMethodSymbol with a SourceOrdinaryMethodSymbolSimple.

I assume we should have at this point only SourceExtensionImplementationMethodSymbol's - right? Or we should handle this case explicitly...