Support `allows ref struct` constraint

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -792,7 +792,7 @@ namespace ICSharpCode.Decompiler.Tests
 			configureDecompiler?.Invoke(settings);
 			var decompiled = await Tester.DecompileCSharp(exeFile, settings).ConfigureAwait(false);
 
-			// 3. Compile
+			// 3. Compare
 			CodeAssert.FilesAreEqual(csFile, decompiled, Tester.GetPreprocessorSymbols(cscOptions).Append("EXPECTED_OUTPUT").ToArray());
 			Tester.RepeatOnIOError(() => File.Delete(decompiled));
 		}

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Generics.cs

@@ -293,6 +293,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		}
 #endif
 
+#if NET90
+		public static void AllowsRefStruct<T>() where T : allows ref struct
+		{
+		}
+#endif
+
 		public static void Issue1959(int a, int b, int? c)
 		{
 			// This line requires parentheses around `a < b` to avoid a grammar ambiguity.

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -2465,7 +2465,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		internal Constraint ConvertTypeParameterConstraint(ITypeParameter tp)
 		{
-			if (!tp.HasDefaultConstructorConstraint && !tp.HasReferenceTypeConstraint && !tp.HasValueTypeConstraint && tp.NullabilityConstraint != Nullability.NotNullable && tp.DirectBaseTypes.All(IsObjectOrValueType))
+			if (!tp.HasDefaultConstructorConstraint && !tp.HasReferenceTypeConstraint && !tp.HasValueTypeConstraint && !tp.AllowsRefLikeType && tp.NullabilityConstraint != Nullability.NotNullable && tp.DirectBaseTypes.All(IsObjectOrValueType))
 			{
 				return null;
 			}
@@ -2518,6 +2518,10 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			{
 				c.BaseTypes.Add(new PrimitiveType("new"));
 			}
+			if (tp.AllowsRefLikeType)
+			{
+				c.BaseTypes.Add(new PrimitiveType("allows ref struct"));
+			}
 			return c;
 		}
 

ICSharpCode.Decompiler/Disassembler/ReflectionDisassembler.cs

@@ -28,6 +28,7 @@ using System.Threading;
 using ICSharpCode.Decompiler.DebugInfo;
 using ICSharpCode.Decompiler.IL;
 using ICSharpCode.Decompiler.Metadata;
+using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.Decompiler.Disassembler
 {
@@ -1733,8 +1734,7 @@ namespace ICSharpCode.Decompiler.Disassembler
 					{
 						output.Write("valuetype ");
 					}
-					const GenericParameterAttributes allowByRefLike = (GenericParameterAttributes)0x0020;
-					if ((gp.Attributes & allowByRefLike) == allowByRefLike)
+					if ((gp.Attributes & TypeUtils.AllowByRefLike) == TypeUtils.AllowByRefLike)
 					{
 						output.Write("byreflike ");
 					}

ICSharpCode.Decompiler/TypeSystem/ITypeParameter.cs

@@ -97,6 +97,11 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </summary>
 		bool HasUnmanagedConstraint { get; }
 
+		/// <summary>
+		/// <see langword="true"/> if the <c>allows ref struct</c> constraint is specified for the type parameter.
+		/// </summary>
+		bool AllowsRefLikeType { get; }
+
 		/// <summary>
 		/// Nullability of the reference type constraint. (e.g. "where T : class?").
 		/// 

ICSharpCode.Decompiler/TypeSystem/Implementation/AbstractTypeParameter.cs

@@ -175,6 +175,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		public abstract bool HasReferenceTypeConstraint { get; }
 		public abstract bool HasValueTypeConstraint { get; }
 		public abstract bool HasUnmanagedConstraint { get; }
+		public abstract bool AllowsRefLikeType { get; }
 		public abstract Nullability NullabilityConstraint { get; }
 
 		public TypeKind Kind {

ICSharpCode.Decompiler/TypeSystem/Implementation/DefaultTypeParameter.cs

@@ -71,6 +71,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		public override bool HasReferenceTypeConstraint => hasReferenceTypeConstraint;
 		public override bool HasDefaultConstructorConstraint => hasDefaultConstructorConstraint;
 		public override bool HasUnmanagedConstraint => false;
+		public override bool AllowsRefLikeType => false;
 		public override Nullability NullabilityConstraint => nullabilityConstraint;
 
 		public override IReadOnlyList<TypeConstraint> TypeConstraints { get; }

ICSharpCode.Decompiler/TypeSystem/Implementation/DummyTypeParameter.cs

@@ -179,6 +179,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		bool ITypeParameter.HasReferenceTypeConstraint => false;
 		bool ITypeParameter.HasValueTypeConstraint => false;
 		bool ITypeParameter.HasUnmanagedConstraint => false;
+		bool ITypeParameter.AllowsRefLikeType => false;
 		Nullability ITypeParameter.NullabilityConstraint => Nullability.Oblivious;
 
 		IReadOnlyList<TypeConstraint> ITypeParameter.TypeConstraints => EmptyList<TypeConstraint>.Instance;

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataTypeParameter.cs

@@ -119,6 +119,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		public override bool HasDefaultConstructorConstraint => (attr & GenericParameterAttributes.DefaultConstructorConstraint) != 0;
 		public override bool HasReferenceTypeConstraint => (attr & GenericParameterAttributes.ReferenceTypeConstraint) != 0;
 		public override bool HasValueTypeConstraint => (attr & GenericParameterAttributes.NotNullableValueTypeConstraint) != 0;
+		public override bool AllowsRefLikeType => (attr & TypeUtils.AllowByRefLike) != 0;
 
 		public override bool HasUnmanagedConstraint {
 			get {

ICSharpCode.Decompiler/TypeSystem/Implementation/NullabilityAnnotatedType.cs

@@ -115,6 +115,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		bool ITypeParameter.HasReferenceTypeConstraint => baseType.HasReferenceTypeConstraint;
 		bool ITypeParameter.HasValueTypeConstraint => baseType.HasValueTypeConstraint;
 		bool ITypeParameter.HasUnmanagedConstraint => baseType.HasUnmanagedConstraint;
+		bool ITypeParameter.AllowsRefLikeType => baseType.AllowsRefLikeType;
 		Nullability ITypeParameter.NullabilityConstraint => baseType.NullabilityConstraint;
 		IReadOnlyList<TypeConstraint> ITypeParameter.TypeConstraints => baseType.TypeConstraints;
 		SymbolKind ISymbol.SymbolKind => SymbolKind.TypeParameter;

ICSharpCode.Decompiler/TypeSystem/Implementation/SpecializedMethod.cs

@@ -278,6 +278,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			public override bool HasReferenceTypeConstraint => baseTp.HasReferenceTypeConstraint;
 			public override bool HasDefaultConstructorConstraint => baseTp.HasDefaultConstructorConstraint;
 			public override bool HasUnmanagedConstraint => baseTp.HasUnmanagedConstraint;
+			public override bool AllowsRefLikeType => baseTp.AllowsRefLikeType;
 
 			public override Nullability NullabilityConstraint => baseTp.NullabilityConstraint;
 

ICSharpCode.Decompiler/TypeSystem/TypeUtils.cs

@@ -16,6 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Reflection;
+
 using ICSharpCode.Decompiler.IL;
 using ICSharpCode.Decompiler.TypeSystem.Implementation;
 
@@ -25,6 +27,8 @@ namespace ICSharpCode.Decompiler.TypeSystem
 	{
 		public const int NativeIntSize = 6; // between 4 (Int32) and 8 (Int64)
 
+		public const GenericParameterAttributes AllowByRefLike = (GenericParameterAttributes)0x0020;
+
 		/// <summary>
 		/// Gets the size (in bytes) of the input type.
 		/// Returns <c>NativeIntSize</c> for pointer-sized types.