PowerShell · iSazonov · Aug 17, 2017 · Aug 11, 2017 · Aug 11, 2017 · Aug 11, 2017
diff --git a/src/System.Management.Automation/engine/COM/ComTypeInfo.cs b/src/System.Management.Automation/engine/COM/ComTypeInfo.cs
@@ -15,6 +15,18 @@ namespace System.Management.Automation
     /// </summary>
     internal class ComTypeInfo
     {
+        /// <summary>
+        /// A member with a DISPID equal to –4 is found on a collection interface.
+        /// This special member, often called '_NewEnum', returns an interface that enables clients to enumerate objects in a collection.
+        /// </summary>
+        internal const int DISPID_NEWENUM = -4;
+
+        /// <summary>
+        /// A member with a DISPID equal to 0 is considered a default member.
+        /// Default members in COM can be transformed to default members in .NET (indexers in C#).
+        /// </summary>
+        internal const int DISPID_DEFAULTMEMBER = 0;
+
         /// <summary>
         ///  Member variables.
         /// </summary>
@@ -44,7 +56,7 @@ internal ComTypeInfo(COM.ITypeInfo info)
         /// <summary>
         ///  Collection of properties in the COM object.
         /// </summary>
-        public Dictionary<String, ComProperty> Properties
+        internal Dictionary<String, ComProperty> Properties
         {
             get
             {
@@ -55,27 +67,31 @@ public Dictionary<String, ComProperty> Properties
         /// <summary>
         ///  Collection of methods in the COM object.
         /// </summary>
-        public Dictionary<String, ComMethod> Methods
+        internal Dictionary<String, ComMethod> Methods
         {
             get
             {
                 return _methods;
             }
         }
 
-
-
         /// <summary>
         ///  Returns the string of the GUID for the type information.
         /// </summary>
-        public string Clsid
+        internal string Clsid
         {
             get
             {
                 return _guid.ToString();
             }
         }
 
+        /// <summary>
+        /// If 'DISPID_NEWENUM' member is present, return the InvokeKind;
+        /// otherwise, return null.
+        /// </summary>
+        internal COM.INVOKEKIND? NewEnumInvokeKind { get; private set; }
+
         /// <summary>
         /// Initializes the typeinfo object
         /// </summary>
@@ -91,6 +107,8 @@ private void Initialize()
                 for (int i = 0; i < typeattr.cFuncs; i++)
                 {
                     COM.FUNCDESC funcdesc = GetFuncDesc(_typeinfo, i);
+                    if (funcdesc.memid == DISPID_NEWENUM) { NewEnumInvokeKind = funcdesc.invkind; }
+
                     if ((funcdesc.wFuncFlags & 0x1) == 0x1)
                     {
                         // http://msdn.microsoft.com/en-us/library/ee488948.aspx

diff --git a/src/System.Management.Automation/engine/COM/ComUtil.cs b/src/System.Management.Automation/engine/COM/ComUtil.cs
@@ -5,6 +5,7 @@
 using System.Runtime.InteropServices;
 using System.Management.Automation.ComInterop;
 using System.Text;
+using System.Collections;
 using System.Collections.ObjectModel;
 using COM = System.Runtime.InteropServices.ComTypes;
 
@@ -355,4 +356,87 @@ internal static ComMethodInformation[] GetMethodInformationArray(COM.ITypeInfo t
             return returnValue;
         }
     }
-}
+
+    /// <summary>
+    /// Defines an enumerator that represent a COM collection object.
+    /// </summary>
+    internal class ComEnumerator : IEnumerator
+    {
+        private COM.IEnumVARIANT _enumVariant;
+        private object[] _element;
+
+        private ComEnumerator(COM.IEnumVARIANT enumVariant)
+        {
+            _enumVariant = enumVariant;
+            _element = new object[1];
+        }
+
+        public object Current
+        {
+            get { return _element[0]; }
+        }
+
+        public bool MoveNext()
+        {
+            _element[0] = null;
+            int result = _enumVariant.Next(1, _element, IntPtr.Zero);
+            return result == 0;
+        }
+
+        public void Reset()
+        {
+            _element[0] = null;
+            _enumVariant.Reset();
+        }
+
+        /// <summary>
+        /// Try to create an enumerator for a COM object.
+        /// </summary>
+        /// <returns>
+        /// A 'ComEnumerator' instance, or null if we cannot create an enumerator for the COM object.
+        /// </returns>
+        internal static ComEnumerator Create(object comObject)
+        {
+            if (comObject == null || !comObject.GetType().IsCOMObject) { return null; }
+
+            // The passed-in COM object could already be a IEnumVARIANT interface.
+            // e.g. user call '_NewEnum()' on a COM collection interface.
+            var enumVariant = comObject as COM.IEnumVARIANT;
+            if (enumVariant != null)
+            {
+                return new ComEnumerator(enumVariant);
+            }
+
+            // The passed-in COM object could be a collection.
+            var enumerable = comObject as IEnumerable;
+            var target = comObject as IDispatch;
+            if (enumerable != null && target != null)
+            {
+                try
+                {
+                    var comTypeInfo = ComTypeInfo.GetDispatchTypeInfo(comObject);
+                    if (comTypeInfo != null && comTypeInfo.NewEnumInvokeKind.HasValue)
+                    {
+                        // The COM object is a collection and also a IDispatch interface, so we try to get a
+                        // IEnumVARIANT interface out of it by invoking its '_NewEnum (DispId: -4)' function.
+                        var result = ComInvoker.Invoke(target, ComTypeInfo.DISPID_NEWENUM,
+                                                        args: Utils.EmptyArray<object>(), byRef: null,
+                                                        invokeKind: comTypeInfo.NewEnumInvokeKind.Value);
+                        enumVariant = result as COM.IEnumVARIANT;
+                        if (enumVariant != null)
+                        {
+                            return new ComEnumerator(enumVariant);
+                        }
+                    }
+                }
+                catch (Exception)
+                {
+                    // Ignore exceptions. In case of exception, no enumerator can be created
+                    // for the passed-in COM object, and we will return null eventually.
+                }
+            }
+
+            return null;
+        }
+    }
+}
diff --git a/src/System.Management.Automation/engine/runtime/Operations/MiscOps.cs b/src/System.Management.Automation/engine/runtime/Operations/MiscOps.cs
@@ -3199,23 +3199,18 @@ internal object GetNonEnumerableObject()
         internal static IEnumerator GetCOMEnumerator(object obj)
         {
             object targetValue = PSObject.Base(obj);
-            try
-            {
-                IEnumerable enumerable = targetValue as IEnumerable;
-                if (enumerable != null)
-                {
-                    var enumerator = enumerable.GetEnumerator();
-                    if (enumerator != null)
-                    {
-                        return enumerator;
-                    }
-                }
-            }
-            catch (Exception)
-            {
-            }
 
-            return targetValue as IEnumerator ?? NonEnumerableObjectEnumerator.Create(obj);
+            // We use ComEnumerator to enumerate COM collections because the following code doesn't work in .NET Core
+            //   IEnumerable enumerable = targetValue as IEnumerable;
+            //   if (enumerable != null)
+            //   {
+            //       var enumerator = enumerable.GetEnumerator();
+            //       ...
+            //   }
+            // The call to 'GetEnumerator()' throws exception because COM is not supported in .NET Core.
+            // See https://github.com/dotnet/corefx/issues/19731 for more information.
+            // When COM support is back to .NET Core, we need to change back to the original implementation.
+            return ComEnumerator.Create(targetValue) ?? NonEnumerableObjectEnumerator.Create(obj);
         }
 
         internal static IEnumerator GetGenericEnumerator<T>(IEnumerable<T> enumerable)

diff --git a/test/powershell/engine/COM/COM.Basic.Tests.ps1 b/test/powershell/engine/COM/COM.Basic.Tests.ps1
@@ -0,0 +1,48 @@
+
+try {
+    $defaultParamValues = $PSdefaultParameterValues.Clone()
+    $PSDefaultParameterValues["it:skip"] = ![System.Management.Automation.Platform]::IsWindowsDesktop
+
+    Describe 'Basic COM Tests' -Tags "CI" {
+        BeforeAll {
+            $null = New-Item -Path $TESTDRIVE/file1 -ItemType File
+            $null = New-Item -Path $TESTDRIVE/file2 -ItemType File
+            $null = New-Item -Path $TESTDRIVE/file3 -ItemType File
+        }
+
+        It "Should enumerate files from a folder" {
+            $shell = New-Object -ComObject "Shell.Application"
+            $folder = $shell.Namespace("$TESTDRIVE")
+            $items = $folder.Items()
+
+            ## $items is a collection of all items belong to the folder, and it should be enumerated.
+            $items | Measure-Object | ForEach-Object Count | Should Be $items.Count
+        }
+
+        It "Should enumerate IEnumVariant interface object without exception" {
+            $shell = New-Object -ComObject "Shell.Application"
+            $folder = $shell.Namespace("$TESTDRIVE")
+            $items = $folder.Items()
+
+            ## $enumVariant is an IEnumVariant interface of all items belong to the folder, and it should be enumerated.
+            $enumVariant = $items._NewEnum()
+            $enumVariant | Measure-Object | ForEach-Object Count | Should Be $items.Count
+        }
+
+        It "Should enumerate drives" {
+            $fileSystem = New-Object -ComObject scripting.filesystemobject
+            $drives = $fileSystem.Drives
+
+            ## $drives is a read-only collection of all available drives, and it should be enumerated.
+            $drives | Measure-Object | ForEach-Object Count | Should Be $drives.Count
+            ## $element should be the first drive from the enumeration. It shouldn't be the same as $drives,
+            ## but it should be the same as '$drives.Item($element.DriveLetter)'
+            $element = $drives | Select-Object -First 1
+            [System.Object]::ReferenceEquals($element, $drives) | Should Be $false
+            $element | Should Be $drives.Item($element.DriveLetter)
+        }
+    }
+
+} finally {
+    $global:PSdefaultParameterValues = $defaultParamValues
+}