Update assert in TypeUnification.CanUnify for substitutions from type...

Update assert in TypeUnification.CanUnify for substitutions from type parameter to type parameter (changeset 1354882)

Src/Compilers/CSharp/Portable/Utilities/TypeUnification.cs

@@ -3,8 +3,6 @@
 using System.Diagnostics;
 using System.Linq;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
-using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis.CSharp
 {
@@ -18,11 +16,29 @@ public static bool CanUnify(TypeSymbol t1, TypeSymbol t2)
         {
             MutableTypeMap substitution = null;
             bool result = CanUnifyHelper(t1, t2, ref substitution);
-            Debug.Assert(!result || (substitution == null && t1 == t2) ||
-                substitution.SubstituteType(t1) == substitution.SubstituteType(t2));
+#if DEBUG
+            Debug.Assert(!result ||
+                SubstituteAllTypeParameters(substitution, t1) == SubstituteAllTypeParameters(substitution, t2));
+#endif
             return result;
         }
 
+#if DEBUG
+        private static TypeSymbol SubstituteAllTypeParameters(AbstractTypeMap substitution, TypeSymbol type)
+        {
+            if (substitution != null)
+            {
+                TypeSymbol previous;
+                do
+                {
+                    previous = type;
+                    type = substitution.SubstituteType(type);
+                } while (type != previous);
+            }
+            return type;
+        }
+#endif
+
         /// <summary>
         /// Determine whether there is any substitution of type parameters that will
         /// make two types identical.

Src/Compilers/CSharp/Test/Symbol/Symbols/TypeUnificationTests.cs

 // Copyright (c) Microsoft Open Technologies, Inc.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using Microsoft.CodeAnalysis.CSharp.Symbols;
-using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
-using Microsoft.CodeAnalysis.Text;
+using Roslyn.Test.Utilities;
 using Xunit;
 
 namespace Microsoft.CodeAnalysis.CSharp.UnitTests
@@ -397,6 +396,24 @@ public class M<U>
             AssertCanUnify(type6, type6);
         }
 
+        [WorkItem(1042692)]
+        [Fact]
+        public void SubstituteWithOtherTypeParameter()
+        {
+            var text =
+@"interface IA<T, U>
+{
+}
+interface IB<T, U> : IA<U, object>, IA<T, U>
+{
+}";
+            var comp = CreateCompilationWithMscorlib(text);
+            var type = comp.GetMember<NamedTypeSymbol>("IB");
+            AssertCanUnify(type.Interfaces[0], type.Interfaces[1]);
+            DiagnosticsUtils.VerifyErrorCodes(comp.GetDiagnostics(),
+                new ErrorDescription { Code = (int)ErrorCode.ERR_UnifyingInterfaceInstantiations, Line = 4, Column = 11 });
+        }
+
         private static void AssertCanUnify(TypeSymbol t1, TypeSymbol t2)
         {
             Assert.True(TypeUnification.CanUnify(t1, t2), string.Format("{0} vs {1}", t1, t2));

Src/Compilers/VisualBasic/Portable/Utilities/TypeUnification.vb

 ' Copyright (c) Microsoft Open Technologies, Inc.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 Imports System.Diagnostics
-Imports Microsoft.CodeAnalysis.Text
 Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
-Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic
 
@@ -19,11 +17,26 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
             Dim substitution As TypeSubstitution = Nothing
             Dim result As Boolean = CanUnifyHelper(containingGenericType, t1, t2, substitution)
-            Debug.Assert(Not result OrElse (substitution Is Nothing AndAlso t1 = t2) OrElse
-                         t1.InternalSubstituteTypeParameters(substitution) = t2.InternalSubstituteTypeParameters(substitution))
+#If DEBUG Then
+            Debug.Assert(Not result OrElse
+                SubstituteAllTypeParameters(substitution, t1) = SubstituteAllTypeParameters(substitution, t2))
+#End If
             Return result
         End Function
 
+#If DEBUG Then
+        Private Shared Function SubstituteAllTypeParameters(substitution As TypeSubstitution, type As TypeSymbol) As TypeSymbol
+            If substitution IsNot Nothing Then
+                Dim previous As TypeSymbol
+                Do
+                    previous = type
+                    type = type.InternalSubstituteTypeParameters(substitution)
+                Loop While previous <> type
+            End If
+            Return type
+        End Function
+#End If
+
         ''' <summary>
         ''' Determine whether there is any substitution of type parameters that will
         ''' make two types identical.

Src/Compilers/VisualBasic/Test/Symbol/SymbolsTests/SymbolErrorTests.vb

 ' Copyright (c) Microsoft Open Technologies, Inc.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 Imports System.Collections.Immutable
-Imports System.IO
-Imports System.Threading
 Imports System.Xml.Linq
 Imports Microsoft.CodeAnalysis.Test.Utilities
-Imports Microsoft.CodeAnalysis.Text
 Imports Microsoft.CodeAnalysis.VisualBasic
 Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
-Imports Microsoft.CodeAnalysis.VisualBasic.UnitTests.Symbols
 Imports Roslyn.Test.Utilities
 Imports Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
 
@@ -15897,6 +15893,27 @@ BC32120: Cannot inherit interface 'interfaceA(Of t2)' because it could be identi
             CompilationUtils.AssertTheseDeclarationDiagnostics(compilation1, expectedErrors1)
         End Sub
 
+        <WorkItem(1042692)>
+        <Fact()>
+        Public Sub BC32120ERR_InterfaceUnifiesWithInterface2_SubstituteWithOtherTypeParameter()
+            Dim compilation1 = CompilationUtils.CreateCompilationWithMscorlib(
+    <compilation>
+        <file name="a.vb"><![CDATA[
+Interface IA(Of T, U)
+End Interface
+Interface IB(Of T, U)
+    Inherits IA(Of U, Object), IA(Of T, U)
+End Interface
+        ]]></file>
+    </compilation>)
+            compilation1.AssertTheseDeclarationDiagnostics(
+                <errors><![CDATA[
+BC32120: Cannot inherit interface 'IA(Of T, U)' because it could be identical to interface 'IA(Of U, Object)' for some type arguments.
+    Inherits IA(Of U, Object), IA(Of T, U)
+                               ~~~~~~~~~~~
+     ]]></errors>)
+        End Sub
+
         <Fact(), WorkItem(543726, "DevDiv")>
         Public Sub BC32121ERR_BaseUnifiesWithInterfaces3()
             Dim compilation1 = CompilationUtils.CreateCompilationWithMscorlib(