corrected and clarified refcounts in TypeLibWrapper and TypeInfoWrapper constructors

Author: WaynePhillipsEA

Rubberduck.VBEEditor/ComManagement/TypeLibs/TypeInfos.cs

@@ -484,7 +484,7 @@ private void InitCommon()
                 // so we cast to our ITypeInfo_Ptrs interface in order to work with the raw IntPtrs
                 IntPtr typeLibPtr = IntPtr.Zero;
                 ((ITypeInfo_Ptrs)target_ITypeInfo).GetContainingTypeLib(out typeLibPtr, out _containerTypeLibIndex);
-                _containerTypeLib = new TypeLibWrapper(typeLibPtr);  // takes ownership of the COM reference
+                _containerTypeLib = new TypeLibWrapper(typeLibPtr, true);  
             }
             catch (Exception e)
             {
@@ -514,6 +514,10 @@ public TypeInfoWrapper(ComTypes.ITypeInfo rawTypeInfo)
         public TypeInfoWrapper(IntPtr rawObjectPtr, int? parentUserFormUniqueId = null)
         {
             _rawObjectPtr = rawObjectPtr;
+            if (_rawObjectPtr == IntPtr.Zero)
+            {
+                throw new ArgumentException("Unepectedly received a null pointer.");
+            }
 
             // We have to restrict interface requests to VBE hosted ITypeInfos due to a bug in their implementation.
             // See TypeInfoWrapper class XML doc for details.
@@ -546,6 +550,8 @@ public void Dispose()
             _ITypeInfo_Aggregator?.Dispose();
             _IVBEComponent_Aggregator?.Dispose();
             _IVBETypeInfo_Aggregator?.Dispose();
+
+            Marshal.Release(_rawObjectPtr);
         }
 
         private TypeLibTextFields? _cachedTextFields;

Rubberduck.VBEEditor/ComManagement/TypeLibs/TypeLibs.cs

@@ -147,9 +147,9 @@ public TypeLibWrapper GetVBEReferenceTypeLibByIndex(int index)
             IntPtr referenceTypeLibPtr = target_IVBEProject.GetReferenceTypeLib(index);
             if (referenceTypeLibPtr == IntPtr.Zero)
             {
-                throw new ArgumentException("$Reference TypeLib not available - probably a missing reference.");
+                throw new ArgumentException("Reference TypeLib not available - probably a missing reference.");
             }
-            return new TypeLibWrapper(referenceTypeLibPtr);
+            return new TypeLibWrapper(referenceTypeLibPtr, isRefCountedInput: true);
         }
 
         public TypeInfoReference GetVBEReferenceByGuid(Guid referenceGuid)
@@ -202,7 +202,7 @@ public static TypeLibWrapper FromVBProject(IVBProject vbProject)
             {
                 // Now we've got the references object, we can read the internal object structure to grab the ITypeLib
                 var internalReferencesObj = StructHelper.ReadComObjectStructure<VBEReferencesObj>(references.Target);
-                return new TypeLibWrapper(internalReferencesObj.TypeLib);
+                return new TypeLibWrapper(internalReferencesObj.TypeLib, isRefCountedInput: false);
             }
         }
 
@@ -217,14 +217,14 @@ private void InitCommon()
         /// Constructor
         /// </summary>
         /// <param name="rawObjectPtr">The raw unamanaged ITypeLib pointer</param>
-        public TypeLibWrapper(IntPtr rawObjectPtr)
+        public TypeLibWrapper(IntPtr rawObjectPtr, bool isRefCountedInput)
         {
             if (!UnmanagedMemHelper.ValidateComObject(rawObjectPtr))
             {
                 throw new ArgumentException("Expected COM object, but validation failed.");
             };
             target_ITypeLib = (ComTypes.ITypeLib)Marshal.GetObjectForIUnknown(rawObjectPtr);
-            Marshal.Release(rawObjectPtr);         // target_ITypeLib holds a reference to this now
+            if (isRefCountedInput) Marshal.Release(rawObjectPtr);         
             InitCommon();
         }
 
@@ -297,7 +297,7 @@ public bool CompileProject()
 #if DEBUG
                 if (e.HResult != (int)KnownComHResults.E_VBA_COMPILEERROR)
                 {
-                    // this is more for debug purposes, as we can probably just return false in future.
+                    // this is for debug purposes, to see if the compiler ever returns other errors on failure
                     throw new ArgumentException("Unrecognised VBE compiler error: \n" + e.ToString());
                 }
 #endif
@@ -466,14 +466,8 @@ public void Dispose()
         IEnumerator IEnumerable.GetEnumerator() => this;
         public IEnumerator<TypeLibWrapper> GetEnumerator() => this;
 
-        public IntPtr GetCurrentReference()
-        {
-            Marshal.AddRef(_currentTypeLibPtr);
-            return _currentTypeLibPtr;
-        }
-
-        TypeLibWrapper IEnumerator<TypeLibWrapper>.Current => new TypeLibWrapper(GetCurrentReference());
-        object IEnumerator.Current => new TypeLibWrapper(GetCurrentReference());
+        TypeLibWrapper IEnumerator<TypeLibWrapper>.Current => new TypeLibWrapper(_currentTypeLibPtr, isRefCountedInput: false);
+        object IEnumerator.Current => new TypeLibWrapper(_currentTypeLibPtr, isRefCountedInput: false);
 
         public void Reset()  // walk back to the first project in the chain
         {