Fix a native integer decoding bug

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/NativeIntegerTypeDecoder.cs

@@ -62,6 +62,7 @@ private TypeSymbol TransformType(TypeSymbol type)
                     return TransformPointerType((PointerTypeSymbol)type);
                 case TypeKind.TypeParameter:
                 case TypeKind.Dynamic:
+                    IgnoreIndex();
                     return type;
                 case TypeKind.Class:
                 case TypeKind.Struct:
@@ -84,6 +85,8 @@ private NamedTypeSymbol TransformNamedType(NamedTypeSymbol type)
                 return _transformFlags[index] ? TransformTypeDefinition(type) : type;
             }
 
+            Debug.Assert(!_transformFlags[index]);
+
             var allTypeArguments = ArrayBuilder<TypeWithAnnotations>.GetInstance();
             type.GetAllTypeArgumentsNoUseSiteDiagnostics(allTypeArguments);
 
@@ -106,13 +109,13 @@ private NamedTypeSymbol TransformNamedType(NamedTypeSymbol type)
 
         private ArrayTypeSymbol TransformArrayType(ArrayTypeSymbol type)
         {
-            Increment();
+            IgnoreIndex();
             return type.WithElementType(TransformTypeWithAnnotations(type.ElementTypeWithAnnotations));
         }
 
         private PointerTypeSymbol TransformPointerType(PointerTypeSymbol type)
         {
-            Increment();
+            IgnoreIndex();
             return type.WithPointedAtType(TransformTypeWithAnnotations(type.PointedAtTypeWithAnnotations));
         }
 
@@ -125,6 +128,12 @@ private int Increment()
             throw new ArgumentException();
         }
 
+        private void IgnoreIndex()
+        {
+            var index = Increment();
+            Debug.Assert(!_transformFlags[index]);
+        }
+
         private static NamedTypeSymbol TransformTypeDefinition(NamedTypeSymbol type)
         {
             switch (type.SpecialType)

src/Compilers/CSharp/Test/Emit/Attributes/AttributeTests_NativeInteger.cs

@@ -916,6 +916,33 @@ public void AttributeFieldExists()
             });
         }
 
+        [Theory]
+        [InlineData("C<dynamic, nint, System.IntPtr>", "C<dynamic, System.IntPtr, System.IntPtr>", "False, False, True, False")]
+        [InlineData("C<dynamic, nuint, System.UIntPtr>", "C<dynamic, System.UIntPtr, System.UIntPtr>", "False, False, True, False")]
+        [InlineData("C<T, nint, System.IntPtr>", "C<T, System.IntPtr, System.IntPtr>", "False, False, True, False")]
+        [InlineData("C<T, nuint, System.UIntPtr>", "C<T, System.UIntPtr, System.UIntPtr>", "False, False, True, False")]
+        public void NestedNativeIntegerWithPrecedingType(string sourceType, string metadataType, string expectedAttribute)
+        {
+            var comp = CompileAndVerify($@"
+class C<T, U, V>
+{{
+    public {sourceType} F;
+}}
+", options: TestOptions.ReleaseDll, parseOptions: TestOptions.RegularPreview, symbolValidator: symbolValidator);
+
+            void symbolValidator(ModuleSymbol module)
+            {
+                var expectedAttributes = $@"
+C<T, U, V>
+    [NativeInteger({{ {expectedAttribute} }})] {metadataType} F";
+
+                AssertNativeIntegerAttributes(module, expectedAttributes);
+                var c = module.GlobalNamespace.GetTypeMember("C");
+                var field = c.GetField("F");
+                Assert.Equal(sourceType, field.Type.ToTestDisplayString());
+            }
+        }
+
         private static TypeDefinition GetTypeDefinitionByName(MetadataReader reader, string name)
         {
             return reader.GetTypeDefinition(reader.TypeDefinitions.Single(h => reader.StringComparer.Equals(reader.GetTypeDefinition(h).Name, name)));