fix: Added DispID offset in case of ComVisible false methods (#246)

* fix: Added DispID offset in case of ComVisible false methods or properties

* fix: Convert CRLF to LF

Author: marklechtermann

src/dscom.test/tests/MemIdTest.cs

@@ -460,13 +460,15 @@ public void IDispatchInterfaceWith3MethodsAndOneComVisibleFalse_MemIdAndVTableSi
         using var method1 = testInterface!.GetFuncDescByName("Method1");
         method1.Should().NotBeNull();
         method1!.Value.oVft.Should().Be(0);
+        method1!.Value.memid.Should().Be((int)Constants.BASE_OLEAUT_DISPID);
 
         using var method2 = testInterface!.GetFuncDescByName("Method2");
         method2.Should().BeNull();
 
         using var method3 = testInterface!.GetFuncDescByName("Method3");
         method3.Should().NotBeNull();
         method3!.Value.oVft.Should().Be(0);
+        method3!.Value.memid.Should().Be(((int)Constants.BASE_OLEAUT_DISPID) + 2);
     }
 
     [Fact]
@@ -491,13 +493,15 @@ public void IDispatchInterfaceWith3PropertiesAndOneComVisibleFalse_MemIdAndVTabl
         using var method1 = testInterface!.GetFuncDescByName("Property1");
         method1.Should().NotBeNull();
         method1!.Value.oVft.Should().Be(0);
+        method1!.Value.memid.Should().Be((int)Constants.BASE_OLEAUT_DISPID);
 
         using var method2 = testInterface!.GetFuncDescByName("Property2");
         method2.Should().BeNull();
 
         using var method3 = testInterface!.GetFuncDescByName("Property3", INVOKEKIND.INVOKE_PROPERTYGET);
         method3.Should().NotBeNull();
         method3!.Value.oVft.Should().Be(0);
+        method3!.Value.memid.Should().Be(((int)Constants.BASE_OLEAUT_DISPID) + 4);
     }
 
     [Fact]
@@ -522,13 +526,15 @@ public void DualInterfaceWith3MethodsAndOneComVisibleFalse_MemIdAndVTableSizeAre
         using var method1 = testInterface!.GetFuncDescByName("Method1");
         method1.Should().NotBeNull();
         method1!.Value.oVft.Should().Be(56);
+        method1!.Value.memid.Should().Be((int)Constants.BASE_OLEAUT_DISPID);
 
         using var method2 = testInterface!.GetFuncDescByName("Method2");
         method2.Should().BeNull();
 
         using var method3 = testInterface!.GetFuncDescByName("Method3");
         method3.Should().NotBeNull();
         method3!.Value.oVft.Should().Be(72);
+        method3!.Value.memid.Should().Be(((int)Constants.BASE_OLEAUT_DISPID) + 2);
     }
 
     [Fact]
@@ -553,13 +559,15 @@ public void DualInterfaceWith3PropertiesAndOneComVisibleFalse_MemIdAndVTableSize
         using var method1 = testInterface!.GetFuncDescByName("Property1");
         method1.Should().NotBeNull();
         method1!.Value.oVft.Should().Be(56);
+        method1!.Value.memid.Should().Be((int)Constants.BASE_OLEAUT_DISPID);
 
         using var method2 = testInterface!.GetFuncDescByName("Property2");
         method2.Should().BeNull();
 
         using var method3 = testInterface!.GetFuncDescByName("Property3", INVOKEKIND.INVOKE_PROPERTYGET);
         method3.Should().NotBeNull();
         method3!.Value.oVft.Should().Be(88);
+        method3!.Value.memid.Should().Be(((int)Constants.BASE_OLEAUT_DISPID) + 4);
     }
 
     [Theory]

src/dscom/DispatchIdCreator.cs

@@ -80,7 +80,7 @@ private void AddDispatchId(uint idGenerated, uint? idFromAttribute, MemberInfo m
         }
     }
 
-    private uint GetNextFreeDispId()
+    internal uint GetNextFreeDispId()
     {
         var dispId = _currentDispId;
         _currentDispId++;

src/dscom/writer/InterfaceWriter.cs

@@ -126,13 +126,22 @@ private void CreateMethodWriters()
         var functionIndex = 0;
         foreach (var methodWriter in MethodWriters)
         {
+            // A methodWriter can be null if ComVisible is false
             if (methodWriter is not null)
             {
                 methodWriter.FunctionIndex = functionIndex;
                 methodWriter.VTableOffset = VTableOffsetUserMethodStart + (index * IntPtr.Size);
                 DispatchIdCreator!.RegisterMember(methodWriter);
                 functionIndex += methodWriter.IsValid ? 1 : 0;
             }
+            else
+            {
+                // In case of ComVisible false, we need to increment the the next free DispId
+                // This offset is needed to keep the DispId in sync with the VTable and the behavior of tlbexp.
+                DispatchIdCreator!.GetNextFreeDispId();
+            }
+
+            // Increment the index for the VTableOffset
             index++;
         }
     }