fix not to set nullability annotation to generic parameters which have no constraints

Author: smdn

src/Smdn.Reflection.ReverseGenerating/Smdn.Reflection.ReverseGenerating/CSharpTypeFormatter.FormatTypeNameWithNullabilityAnnotation.cs

@@ -104,6 +104,10 @@ FormatTypeNameOptions options
         .Append(nullabilityAnnotationForByRefParameter);
     }
 
+    if (targetType.IsGenericParameter && targetType.HasGenericParameterNoConstraints())
+      // generic parameter which has no constraints must not have nullability annotation
+      return builder.Append(GetTypeName(targetType, options));
+
     if (!targetType.IsGenericParameter) {
       if (targetType.IsNested && options.WithDeclaringTypeName)
         builder.Append(FormatTypeNameCore(targetType.GetDeclaringTypeOrThrow(), options)).Append('.');

src/Smdn.Reflection.ReverseGenerating/Smdn.Reflection/TypeGenericParameterExtensions.cs

@@ -77,4 +77,16 @@ genericParameter.DeclaringMethod is not null &&
       continue;
     }
   }
+
+  public static bool HasGenericParameterNoConstraints(this Type genericParameter)
+  {
+    ValidateGenericParameterArgument(genericParameter, nameof(genericParameter));
+
+    var genericParameterConstraintAttrs = genericParameter.GenericParameterAttributes & GenericParameterAttributes.SpecialConstraintMask;
+
+    if (genericParameterConstraintAttrs != GenericParameterAttributes.None)
+      return false;
+
+    return !HasGenericParameterNotNullConstraint(genericParameter);
+  }
 }

tests/Smdn.Reflection.ReverseGenerating/Smdn.Reflection.ReverseGenerating/Generator.MemberDeclaration.Parameters.NullabilityAnnotations.cs

@@ -141,6 +141,38 @@ public void RefType(string p) { }
     [MemberDeclarationTestCase($"public void {nameof(NullableRefType)}(string p) {{}}", MemberEnableNullabilityAnnotations = false)]
     [MemberDeclarationTestCase($"public void {nameof(NullableRefType)}(string? p) {{}}", MemberEnableNullabilityAnnotations = true)]
     public void NullableRefType(string? p) { }
+
+    [MemberDeclarationTestCase($"public void {nameof(GenericType)}<T>(T p) {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(GenericType)}<T>(T p) {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void GenericType<T>(T p) { }
+
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericType)}<T>(T p) {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericType)}<T>(T p) {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void NullableGenericType<T>(T? p) { }
+
+    [MemberDeclarationTestCase($"public void {nameof(GenericNotNullType)}<TNotNull>(TNotNull p) where TNotNull : notnull {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(GenericNotNullType)}<TNotNull>(TNotNull p) where TNotNull : notnull {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void GenericNotNullType<TNotNull>(TNotNull p) where TNotNull : notnull { }
+
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericNotNullType)}<TNotNull>(TNotNull p) where TNotNull : notnull {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericNotNullType)}<TNotNull>(TNotNull? p) where TNotNull : notnull {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void NullableGenericNotNullType<TNotNull>(TNotNull? p) where TNotNull : notnull { }
+
+    [MemberDeclarationTestCase($"public void {nameof(GenericValueType)}<TValue>(TValue p) where TValue : struct {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(GenericValueType)}<TValue>(TValue p) where TValue : struct {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void GenericValueType<TValue>(TValue p) where TValue : struct { }
+
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericValueType)}<TValue>(TValue? p) where TValue : struct {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericValueType)}<TValue>(TValue? p) where TValue : struct {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void NullableGenericValueType<TValue>(TValue? p) where TValue : struct { }
+
+    [MemberDeclarationTestCase($"public void {nameof(GenericRefType)}<TRef>(TRef p) where TRef : class {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(GenericRefType)}<TRef>(TRef p) where TRef : class {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void GenericRefType<TRef>(TRef p) where TRef : class { }
+
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericRefType)}<TRef>(TRef p) where TRef : class {{}}", MemberEnableNullabilityAnnotations = false)]
+    [MemberDeclarationTestCase($"public void {nameof(NullableGenericRefType)}<TRef>(TRef? p) where TRef : class {{}}", MemberEnableNullabilityAnnotations = true)]
+    public void NullableGenericRefType<TRef>(TRef? p) where TRef : class { }
   }
 }
 #endif