[ILVerify] Instantiate generic constraints on initialization (#4758)

* Implemented InstantiatedGenericParameter in order to be able to correctly cast constraints with generic parameter instantiations.

* Added test case for casting constrained generic with generic parameter inside constraint.

* Changed InstantiatedGenericParameter to be able to handle complex generic constraints.

* Added GetInstantiatedGenericParameter to TypeSystemContext.

* Changed generic type / method instantation to be created by InstantiatedGenericParameter.

4 files changed, 133 insertions, 8 deletions

diff --git a/src/ILVerify/src/ILImporter.Verify.cs b/src/ILVerify/src/ILImporter.Verify.cs
index 41ce6434a..3ebc18f9b 100644
--- a/src/ILVerify/src/ILImporter.Verify.cs
+++ b/src/ILVerify/src/ILImporter.Verify.cs
@@ -40,7 +40,6 @@ namespace Internal.IL
         readonly MethodDesc _method;
         readonly MethodSignature _methodSignature;
         readonly TypeSystemContext _typeSystemContext;
-        readonly InstantiationContext _instantiationContext;
 
         readonly TypeDesc _thisType;
 
@@ -154,16 +153,21 @@ namespace Internal.IL
             var instantiatedMethod = method;
             if (instantiatedType.HasInstantiation)
             {
-                instantiatedType = _typeSystemContext.GetInstantiatedType((MetadataType)instantiatedType, instantiatedType.Instantiation);
+                Instantiation genericTypeInstantiation = InstantiatedGenericParameter.CreateGenericTypeInstantiaton(instantiatedType.Instantiation);
+                instantiatedType = _typeSystemContext.GetInstantiatedType((MetadataType)instantiatedType, genericTypeInstantiation);
                 instantiatedMethod = _typeSystemContext.GetMethodForInstantiatedType(instantiatedMethod.GetTypicalMethodDefinition(), (InstantiatedType)instantiatedType);
             }
 
             if (instantiatedMethod.HasInstantiation)
-                instantiatedMethod = _typeSystemContext.GetInstantiatedMethod(instantiatedMethod, instantiatedMethod.Instantiation);
+            {
+                Instantiation genericMethodInstantiation = InstantiatedGenericParameter.CreateGenericMethodInstantiation(
+                    instantiatedType.Instantiation, instantiatedMethod.Instantiation);
+                instantiatedMethod = _typeSystemContext.GetInstantiatedMethod(instantiatedMethod, genericMethodInstantiation);
+            }
             _method = instantiatedMethod;
+
             _methodSignature = _method.Signature;
             _methodIL = method == instantiatedMethod ? methodIL : new InstantiatedMethodIL(instantiatedMethod, methodIL);
-            _instantiationContext = new InstantiationContext(instantiatedType.Instantiation, instantiatedMethod.Instantiation);
 
             // Determine this type
             if (!_method.Signature.IsStatic)
@@ -1293,9 +1297,9 @@ again:
             }
 
             // Check any constraints on the callee's class and type parameters
-            if (!method.OwningType.CheckConstraints(_instantiationContext))
+            if (!method.OwningType.CheckConstraints())
                 VerificationError(VerifierError.UnsatisfiedMethodParentInst, method.OwningType);
-            else if (!method.CheckConstraints(_instantiationContext))
+            else if (!method.CheckConstraints())
                 VerificationError(VerifierError.UnsatisfiedMethodInst, method);
 
             Check(_method.OwningType.CanAccess(method, instance), VerifierError.MethodAccess);
@@ -1404,9 +1408,9 @@ again:
             }
 
             // Check any constraints on the callee's class and type parameters
-            if (!method.OwningType.CheckConstraints(_instantiationContext))
+            if (!method.OwningType.CheckConstraints())
                 VerificationError(VerifierError.UnsatisfiedMethodParentInst, method.OwningType);
-            else if (!method.CheckConstraints(_instantiationContext))
+            else if (!method.CheckConstraints())
                 VerificationError(VerifierError.UnsatisfiedMethodInst, method);
 
             Check(_method.OwningType.CanAccess(method, instance), VerifierError.MethodAccess);
diff --git a/src/ILVerify/src/ILVerify.csproj b/src/ILVerify/src/ILVerify.csproj
index 615183886..73c0208a6 100644
--- a/src/ILVerify/src/ILVerify.csproj
+++ b/src/ILVerify/src/ILVerify.csproj
@@ -17,6 +17,7 @@
     <Compile Include="SimpleTypeSystemContext.cs" />
     <Compile Include="VerifierError.cs" />
     <Compile Include="TypeSystemHelpers.cs" />
+    <Compile Include="InstantiatedGenericParameter.cs" />
     <Compile Include="AccessVerificationHelpers.cs" />
   </ItemGroup>
 
diff --git a/src/ILVerify/src/InstantiatedGenericParameter.cs b/src/ILVerify/src/InstantiatedGenericParameter.cs
new file mode 100644
index 000000000..a767de4fe
--- /dev/null
+++ b/src/ILVerify/src/InstantiatedGenericParameter.cs
@@ -0,0 +1,96 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace Internal.TypeSystem
+{
+    internal sealed partial class InstantiatedGenericParameter : GenericParameterDesc
+    {
+        private readonly GenericParameterDesc _genericParam;
+        private Instantiation _typeInstantiation;
+        private Instantiation _methodInstantiation;
+
+        public GenericParameterDesc GenericParameter
+        {
+            get
+            {
+                return _genericParam;
+            }
+        }
+
+        internal static Instantiation CreateGenericTypeInstantiaton(Instantiation instantiation)
+        {
+            if (instantiation.Length == 0)
+                return instantiation;
+
+            var genericInstantiation = CreateGenericInstantiation(instantiation);
+
+            foreach (var parameter in genericInstantiation)
+                ((InstantiatedGenericParameter)parameter)._typeInstantiation = genericInstantiation;
+
+            return genericInstantiation;
+        }
+
+        internal static Instantiation CreateGenericMethodInstantiation(Instantiation typeInstantiation, Instantiation methodInstantiation)
+        {
+            if (methodInstantiation.Length == 0)
+                return methodInstantiation;
+
+            var genericInstantiation = CreateGenericInstantiation(methodInstantiation);
+
+            foreach (var parameter in genericInstantiation)
+            {
+                var par = (InstantiatedGenericParameter)parameter;
+                par._typeInstantiation = typeInstantiation;
+                par._methodInstantiation = genericInstantiation;
+            }
+
+            return genericInstantiation;
+        }
+
+        private static Instantiation CreateGenericInstantiation(Instantiation fromInstantiation)
+        {
+            var parameters = new TypeDesc[fromInstantiation.Length];
+            for (int i = 0; i < fromInstantiation.Length; ++i)
+                parameters[i] = new InstantiatedGenericParameter((GenericParameterDesc)fromInstantiation[i]);
+
+            return new Instantiation(parameters);
+        }
+
+        private InstantiatedGenericParameter(GenericParameterDesc genericParam)
+        {
+            Debug.Assert(!(genericParam is InstantiatedGenericParameter));
+            _genericParam = genericParam;
+        }
+
+        public override GenericParameterKind Kind => _genericParam.Kind;
+
+        public override int Index => _genericParam.Index;
+
+        public override TypeSystemContext Context => _genericParam.Context;
+
+        public override GenericVariance Variance => _genericParam.Variance;
+
+        public override GenericConstraints Constraints => _genericParam.Constraints;
+
+        public override IEnumerable<TypeDesc> TypeConstraints
+        {
+            get
+            {
+                foreach (var constraint in _genericParam.TypeConstraints)
+                {
+                    yield return constraint.InstantiateSignature(_typeInstantiation, _methodInstantiation);
+                }
+            }
+        }
+
+        public override string ToString()
+        {
+            return _genericParam.ToString();
+        }
+    }
+}
diff --git a/src/ILVerify/tests/ILTests/CastingTests.il b/src/ILVerify/tests/ILTests/CastingTests.il
index 8387ea85f..4be6b764e 100644
--- a/src/ILVerify/tests/ILTests/CastingTests.il
+++ b/src/ILVerify/tests/ILTests/CastingTests.il
@@ -104,6 +104,30 @@
         stloc.0
         ret
     }
+
+    .method static public hidebysig void Assign.ConstrainedGenericToComparable_Valid<(class [System.Runtime]System.IComparable`1<!!T>) T>(!!T t)
+    {
+        .locals init (
+            class [System.Runtime]System.IComparable`1<!!T> c
+        )
+
+        ldarg.0
+        box     !!T
+        stloc.0
+        ret
+    }
+
+    .method static public hidebysig void Assign.ComplexConstrainedGenericToComparable_Valid<(!!S) T, (class [System.Runtime]System.IComparable`1<!!T>) S>(!!T t)
+    {
+        .locals init (
+            class [System.Runtime]System.IComparable`1<!!T> c
+        )
+
+        ldarg.0
+        box     !!T
+        stloc.0
+        ret
+    }
 }
 
 .class public sequential ansi sealed beforefieldinit GenericOtherFieldsType`1<T>