Merge pull request #3708 from WaynePhillipsEA/rewite-comwrapperenumer…

…ation

Rewite of ComWrapperEnumeration, to take control of when IEnumVariant RCW's get released.

Rubberduck.VBEEditor/SafeComWrappers/ComWrapperEnumerator.cs

@@ -1,39 +1,143 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Linq;
+using System.Runtime.InteropServices;
+using ComTypes = System.Runtime.InteropServices.ComTypes;
 
 namespace Rubberduck.VBEditor.SafeComWrappers
 {
+    // The CLR automagically handles COM enumeration by custom marshalling IEnumVARIANT to a managed class (see EnumeratorToEnumVariantMarshaler)
+    // But as we need explicit control over all COM objects in RD, this is unacceptable.  We need to obtain the explicit IEnumVARIANT interface
+    // and ensure this RCW is destroyed in a timely fashion, using Marshal.ReleaseComObject.
+    // The automatic custom marshalling of the enumeration getter method (DISPID_ENUM) prohibits access to the underlying IEnumVARIANT interface.
+    // To work around it, we must call the IDispatch:::Invoke method directly (instead of using CLRs normal late-bound method calling ability).
+
+    [ComImport(), Guid("00020400-0000-0000-C000-000000000046")]
+    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]        
+    interface IDispatch
+    {
+        [PreserveSig] int GetTypeInfoCount([Out] out uint pctinfo);
+        [PreserveSig] int GetTypeInfo([In] uint iTInfo, [In] uint lcid, [Out] out ComTypes.ITypeInfo pTypeInfo);
+        [PreserveSig] int GetIDsOfNames([In] ref Guid riid, [In] string[] rgszNames, [In] uint cNames, [In] uint lcid, [Out] out int[] rgDispId);
+
+        [PreserveSig]
+        int Invoke([In] int dispIdMember,
+            [In] ref Guid riid,
+            [In] uint lcid,
+            [In] uint dwFlags,
+            [In, Out] ref ComTypes.DISPPARAMS pDispParams,
+            [Out] out Object pVarResult,
+            [In, Out] ref ComTypes.EXCEPINFO pExcepInfo,
+            [Out] out uint pArgErr);
+    }
+
+    class IDispatchHelper
+    {
+        public enum StandardDispIds : int
+        {
+            DISPID_ENUM = -4
+        }
+
+        public enum InvokeKind : int
+        {
+            DISPATCH_METHOD = 1,
+            DISPATCH_PROPERTYGET = 2,
+            DISPATCH_PROPERTYPUT = 4,
+            DISPATCH_PROPERTYPUTREF = 8,
+        }
+
+        public static object PropertyGet_NoArgs(IDispatch obj, int memberId)
+        {
+            var pDispParams = new ComTypes.DISPPARAMS();
+            object pVarResult;
+            var pExcepInfo = new ComTypes.EXCEPINFO();
+            uint ErrArg;
+            Guid guid = new Guid();
+
+            int hr = obj.Invoke(memberId, ref guid, 0, (uint)(InvokeKind.DISPATCH_METHOD | InvokeKind.DISPATCH_PROPERTYGET), 
+                                    ref pDispParams, out pVarResult, ref pExcepInfo, out ErrArg);
+
+            if (hr < 0)
+            {
+                // could expand this to better handle DISP_E_EXCEPTION
+                throw Marshal.GetExceptionForHR(hr);
+            }
+
+            return pVarResult;
+        }
+    }
+
+    [ComImport(), Guid("00020404-0000-0000-C000-000000000046")]
+    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    public interface IEnumVARIANT
+    {
+        // rgVar is technically an unmanaged array here, but we only ever call with celt=1, so this is compatible.
+        [PreserveSig] int Next([In] uint celt, [Out] out object rgVar, [Out] out uint pceltFetched);
+
+        [PreserveSig] int Skip([In] uint celt);
+        [PreserveSig] int Reset();
+        [PreserveSig] int Clone([Out] out IEnumVARIANT retval);
+    }
+
     public class ComWrapperEnumerator<TWrapperItem> : IEnumerator<TWrapperItem>
         where TWrapperItem : class
     {
         private readonly Func<object, TWrapperItem> _itemWrapper;
-        private readonly IEnumerator _internal;
+        private readonly IEnumVARIANT _enumeratorRCW;
+        private TWrapperItem _currentItem;
 
-        public ComWrapperEnumerator(IEnumerable source, Func<object, TWrapperItem> itemWrapper)
+        public ComWrapperEnumerator(object source, Func<object, TWrapperItem> itemWrapper)
         {
             _itemWrapper = itemWrapper;
-            _internal = source?.GetEnumerator() ?? Enumerable.Empty<TWrapperItem>().GetEnumerator();
+
+            if (source != null)
+            {
+                _enumeratorRCW = (IEnumVARIANT)IDispatchHelper.PropertyGet_NoArgs((IDispatch)source, (int)IDispatchHelper.StandardDispIds.DISPID_ENUM);
+                ((IEnumerator)this).Reset();  // precaution 
+            }
         }
 
         public void Dispose()
         {
-            // nothing to dispose here
+            if (!IsWrappingNullReference) Marshal.ReleaseComObject(_enumeratorRCW);
         }
 
-        public bool MoveNext()
+        void IEnumerator.Reset()
         {
-            return _internal.MoveNext();
+            if (!IsWrappingNullReference)
+            {
+                int hr = _enumeratorRCW.Reset();      
+                if (hr < 0)
+                {
+                    throw Marshal.GetExceptionForHR(hr);
+                }
+            }
         }
+
+        public bool IsWrappingNullReference => _enumeratorRCW == null;
+
+        public TWrapperItem Current => _currentItem; 
+        object IEnumerator.Current => _currentItem;
 
-        public void Reset()
+        bool IEnumerator.MoveNext()
         {
-            _internal.Reset();
-        }
+            if (IsWrappingNullReference) return false;
+
+            _currentItem = null;
 
-        public TWrapperItem Current => _itemWrapper.Invoke(_internal.Current);
+            object currentItemRCW;
+            uint celtFetched;
+            int hr = _enumeratorRCW.Next(1, out currentItemRCW, out celtFetched);
+            // hr == S_FALSE (1) or S_OK (0), or <0 means error
 
-        object IEnumerator.Current => Current;
+            _currentItem = _itemWrapper.Invoke(currentItemRCW);     // creates a null wrapped reference even on end/error, just as a precaution
+
+            if (hr < 0)
+            {
+                throw Marshal.GetExceptionForHR(hr);
+            }
+
+            return (celtFetched == 1);      // celtFetched will be 0 when we reach the end of the collection
+        }
     }
 }

Rubberduck.VBEEditor/SafeComWrappers/Office.Core/CommandBarControls.cs

@@ -31,9 +31,7 @@ public ICommandBarControl Add(ControlType type, int before)
 
         IEnumerator<ICommandBarControl> IEnumerable<ICommandBarControl>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<ICommandBarControl>(null, o => new CommandBarControl(null))
-                : new ComWrapperEnumerator<ICommandBarControl>(Target,
+            return new ComWrapperEnumerator<ICommandBarControl>(Target,
                     comObject => new CommandBarControl((Microsoft.Office.Core.CommandBarControl) comObject));
         }
 

Rubberduck.VBEEditor/SafeComWrappers/Office.Core/CommandBars.cs

@@ -57,9 +57,7 @@ public ICommandBarControl FindControl(ControlType type, int id)
 
         IEnumerator<ICommandBar> IEnumerable<ICommandBar>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<ICommandBar>(null, o => new CommandBar(null))
-                : new ComWrapperEnumerator<ICommandBar>(Target,
+            return new ComWrapperEnumerator<ICommandBar>(Target,
                     comObject => new CommandBar((Microsoft.Office.Core.CommandBar) comObject));
         }
 

Rubberduck.VBEEditor/SafeComWrappers/VB6/VBComponents.cs

@@ -69,9 +69,7 @@ public IVBComponent AddMTDesigner(int index = 0)
 
         IEnumerator<IVBComponent> IEnumerable<IVBComponent>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IVBComponent>(null, o => new VBComponent(null))
-                : new ComWrapperEnumerator<IVBComponent>(Target, comObject => new VBComponent((VB.VBComponent)comObject));
+            return new ComWrapperEnumerator<IVBComponent>(Target, comObject => new VBComponent((VB.VBComponent)comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VB6/VBProjects.cs

@@ -54,9 +54,7 @@ public IVBProject Open(string path)
 
         IEnumerator<IVBProject> IEnumerable<IVBProject>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IVBProject>(null, o => new VBProject(null))
-                : new ComWrapperEnumerator<IVBProject>(Target, comObject => new VBProject((VB.VBProject)comObject));
+            return new ComWrapperEnumerator<IVBProject>(Target, comObject => new VBProject((VB.VBProject)comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/AddIns.cs

@@ -48,9 +48,7 @@ IEnumerator IEnumerable.GetEnumerator()
 
         IEnumerator<IAddIn> IEnumerable<IAddIn>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IAddIn>(null, o => new AddIn(null))
-                : new ComWrapperEnumerator<IAddIn>(Target, comObject => new AddIn((VB.AddIn) comObject));
+            return new ComWrapperEnumerator<IAddIn>(Target, comObject => new AddIn((VB.AddIn) comObject));
         }
     }
 }

Rubberduck.VBEEditor/SafeComWrappers/VBA/CodePanes.cs

@@ -28,9 +28,7 @@ public ICodePane Current
 
         IEnumerator<ICodePane> IEnumerable<ICodePane>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<ICodePane>(null, o => new CodePane(null))
-                : new ComWrapperEnumerator<ICodePane>(Target, comObject => new CodePane((VB.CodePane) comObject));
+            return new ComWrapperEnumerator<ICodePane>(Target, comObject => new CodePane((VB.CodePane) comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/Controls.cs

@@ -20,9 +20,7 @@ public Controls(VB.Forms.Controls target, bool rewrapping = false)
         IEnumerator<IControl> IEnumerable<IControl>.GetEnumerator()
         {
             // soft-casting because ImageClass doesn't implement IControl
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IControl>(null, o => new Control(null))
-                : new ComWrapperEnumerator<IControl>(Target, comObject => new Control(comObject as VB.Forms.Control));
+            return new ComWrapperEnumerator<IControl>(Target, comObject => new Control(comObject as VB.Forms.Control));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/LinkedWindows.cs

@@ -47,9 +47,7 @@ IEnumerator IEnumerable.GetEnumerator()
 
         IEnumerator<IWindow> IEnumerable<IWindow>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IWindow>(null, o => new Window(null))
-                : new ComWrapperEnumerator<IWindow>(Target, comObject => new Window((VB.Window) comObject));
+            return new ComWrapperEnumerator<IWindow>(Target, comObject => new Window((VB.Window) comObject));
         }
 
         public override bool Equals(ISafeComWrapper<VB.LinkedWindows> other)

Rubberduck.VBEEditor/SafeComWrappers/VBA/Properties.cs

@@ -24,9 +24,7 @@ public Properties(VB.Properties target, bool rewrapping = false)
 
         IEnumerator<IProperty> IEnumerable<IProperty>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IProperty>(null, o => new Property(null))
-                : new ComWrapperEnumerator<IProperty>(Target, comObject => new Property((VB.Property) comObject));
+            return new ComWrapperEnumerator<IProperty>(Target, comObject => new Property((VB.Property) comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/References.cs

@@ -96,9 +96,7 @@ public void Remove(IReference reference)
 
         IEnumerator<IReference> IEnumerable<IReference>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IReference>(null, o => new Reference(null))
-                : new ComWrapperEnumerator<IReference>(Target, comObject => new Reference((VB.Reference) comObject));
+            return new ComWrapperEnumerator<IReference>(Target, comObject => new Reference((VB.Reference) comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/VBComponents.cs

@@ -72,9 +72,7 @@ public IVBComponent AddMTDesigner(int index = 0)
 
         IEnumerator<IVBComponent> IEnumerable<IVBComponent>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IVBComponent>(null, o => new VBComponent(null))
-                : new ComWrapperEnumerator<IVBComponent>(Target, comObject => new VBComponent((VB.VBComponent) comObject));
+            return new ComWrapperEnumerator<IVBComponent>(Target, comObject => new VBComponent((VB.VBComponent) comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/VBProjects.cs

@@ -60,9 +60,7 @@ public IVBProject Open(string path)
 
         IEnumerator<IVBProject> IEnumerable<IVBProject>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IVBProject>(null, o => new VBProject(null))
-                : new ComWrapperEnumerator<IVBProject>(Target, comObject => new VBProject((VB.VBProject) comObject));
+            return new ComWrapperEnumerator<IVBProject>(Target, comObject => new VBProject((VB.VBProject) comObject));
         }
 
         IEnumerator IEnumerable.GetEnumerator()

Rubberduck.VBEEditor/SafeComWrappers/VBA/Windows.cs

@@ -53,9 +53,7 @@ IEnumerator IEnumerable.GetEnumerator()
 
         IEnumerator<IWindow> IEnumerable<IWindow>.GetEnumerator()
         {
-            return IsWrappingNullReference
-                ? new ComWrapperEnumerator<IWindow>(null, o => new Window(null))
-                : new ComWrapperEnumerator<IWindow>(Target, comObject => new Window((VB.Window) comObject));
+            return new ComWrapperEnumerator<IWindow>(Target, comObject => new Window((VB.Window) comObject));
         }
 
         public override bool Equals(ISafeComWrapper<VB.Windows> other)