Version Used:
.NET 10 SDK (10.0.100)
Compiler version: '5.0.0-2.25523.111 (b0f34d51)'. Language version: 14.0
Steps to Reproduce:
Create a class library project and a console app referencing it:
> mkdir repro && cd repro
> mkdir ReproLib && pushd ReproLib && dotnet new classlib && popd
> mkdir TestConsumer && pushd TestConsumer && dotnet new console && dotnet add reference ../ReproLib && popd
Ref. https://learn.microsoft.com/dotnet/csharp/language-reference/proposals/csharp-14.0/extensions#nullability-and-attributes edit ReproLib/Class1.cs and replace its content with:
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
[assembly: InternalsVisibleTo("TestConsumer")]
namespace ReproLib;
internal static class Extensions {
extension([NotNullWhen(false)] string? text) {
internal bool IsEmpty => string.IsNullOrEmpty(text);
internal bool IsWhitespace => string.IsNullOrWhiteSpace(text);
}
}This defines a couple of internal extension properties, but note also makes internals visible to the TestConsumer assembly.
Edit TestConsumer/Program.cs and replace its content with:
using System.Diagnostics;
using ReproLib;
static class Program {
static void Main() {
Debug.Assert((null as string).IsEmpty);
Debug.Assert("".IsEmpty);
Debug.Assert("\t".IsEmpty is false);
Debug.Assert((null as string).IsWhitespace);
Debug.Assert("".IsWhitespace);
Debug.Assert("\t".IsWhitespace);
}
}Build the TestConsumer project:
> cd TestConsumer && dotnet build
Expected Behavior:
The compilation to succeed since internal types and members were explicitly exposed to TestConsumer.
Actual Behavior:
Every use of internal extension properties defined in ReproLib is flagged with error CS0570 in TestConsumer:
Restore complete (0.2s)
ReproLib net10.0 succeeded (0.9s) → ~/repro/ReproLib/bin/Debug/net10.0/ReproLib.dll
TestConsumer net10.0 failed with 8 error(s) (0.1s)
~/repro/TestConsumer/Program.cs(9,39): error CS0570: 'Extensions.extension(string?).IsEmpty.get' is not supported by the language
~/repro/TestConsumer/Program.cs(10,25): error CS0570: 'Extensions.extension(string?).IsEmpty.get' is not supported by the language
~/repro/TestConsumer/Program.cs(11,27): error CS0570: 'Extensions.extension(string?).IsEmpty.get' is not supported by the language
~/repro/TestConsumer/Program.cs(13,39): error CS0570: 'Extensions.extension(string?).IsWhitespace.get' is not supported by the language
~/repro/TestConsumer/Program.cs(14,25): error CS0570: 'Extensions.extension(string?).IsWhitespace.get' is not supported by the language
~/repro/TestConsumer/Program.cs(15,27): error CS0570: 'Extensions.extension(string?).IsWhitespace.get' is not supported by the language
~/repro/TestConsumer/Program.cs(16,27): error CS0570: 'Extensions.extension(string?).IsWhitespace.get' is not supported by the language
This is unexpected; using classic extension methods here would compile without issue.
Is this a bug or a missing feature, or is C# 14 designed not to allow internal extension properties to be used from other assemblies despite InternalsVisibleTo?
Version Used:
.NET 10 SDK (10.0.100)
Compiler version: '5.0.0-2.25523.111 (b0f34d51)'. Language version: 14.0
Steps to Reproduce:
Create a class library project and a console app referencing it:
Ref. https://learn.microsoft.com/dotnet/csharp/language-reference/proposals/csharp-14.0/extensions#nullability-and-attributes edit
ReproLib/Class1.csand replace its content with:This defines a couple of
internalextension properties, but note also makes internals visible to theTestConsumerassembly.Edit
TestConsumer/Program.csand replace its content with:Build the
TestConsumerproject:Expected Behavior:
The compilation to succeed since internal types and members were explicitly exposed to
TestConsumer.Actual Behavior:
Every use of internal extension properties defined in
ReproLibis flagged with error CS0570 inTestConsumer:This is unexpected; using classic extension methods here would compile without issue.
Is this a bug or a missing feature, or is C# 14 designed not to allow internal extension properties to be used from other assemblies despite
InternalsVisibleTo?