VB.NET anonymous types decompile to invalid C# (VB$AnonymousType_* use sites, hidden definitions)

[siegfriedpammer]

Decompiling VB.NET-compiled assemblies that use anonymous types produces uncompilable C#: anonymous type definitions are hidden from the output, but use sites still reference them by their metadata name.

Reproduction

• NuGet package QuartzNetWebConsole 1.0.2, assembly QuartzNetWebConsole.Views.dll (VB.NET-compiled), current master, default DecompilerSettings.
• Decompile e.g. QuartzNetWebConsole.Views.Views (or any member using VB anonymous types / LINQ Select ... Into).

Observed

Use sites emit the raw generated names, which are not valid C#:

select new VB$AnonymousType_2<TriggerWithState, ITrigger>(tr, tr.Trigger) into $VB$It
select new VB$AnonymousType_3<VB$AnonymousType_2<TriggerWithState, ITrigger>, bool>($VB$It, ...) into $VB$It

At the same time DecompileTypeAsString(new FullTypeName("VB$AnonymousType_02"))` yields an empty string, i.e. the definition is suppressed, so the emitted code has no declaration to fall back on.

Analysis

Two generated-name predicates disagree about VB names:

• SRMExtensions.IsGeneratedName treats names containing $ as generated, and SRMExtensions.IsAnonymousType therefore matches VB$AnonymousType_*. This is what CSharpDecompiler.MemberIsHidden uses (CSharpDecompiler.cs:389), so the definitions are hidden when settings.AnonymousTypes is on.
• NRExtensions.HasGeneratedName(IType) only matches names starting with/containing <, so the type-system-level NRExtensions.IsAnonymousType(IType) returns false for VB$AnonymousType_*. As a result none of the anonymous-type translation paths in CallBuilder/ExpressionBuilder (e.g. CallBuilder.cs:1412/1838) fire for VB assemblies, and no new { ... } is synthesized.

Aligning NRExtensions.IsAnonymousType/HasGeneratedName with the SRM-level predicate should make VB anonymous types round-trip like the C# ones (<>f__AnonymousType*).

Related, likely a separate work item: VB also emits VB$AnonymousDelegate_* types (visible in the first snippet's generic arguments). C# has no equivalent construct, so those would additionally need mapping to Func<...>/Action<...> or a synthesized named delegate to make the output compilable.

This issue was written by an AI agent (Claude) on Siegfried's behalf.