Fix invalid cast of type parameter (#2643)

Author: sbomer

src/ILLink.RoslynAnalyzer/RequiresAnalyzerBase.cs

@@ -172,10 +172,10 @@ public override void Initialize (AnalysisContext context)
 					for (int i = 0; i < typeParams.Length; i++) {
 						var typeParam = typeParams[i];
 						var typeArg = typeArgs[i];
-						if (!typeParam.HasConstructorConstraint)
+						if (!typeParam.HasConstructorConstraint ||
+							typeArg is not INamedTypeSymbol { InstanceConstructors: { } typeArgCtors })
 							continue;
 
-						var typeArgCtors = ((INamedTypeSymbol) typeArg).InstanceConstructors;
 						foreach (var instanceCtor in typeArgCtors) {
 							if (instanceCtor.Arity > 0)
 								continue;

test/Mono.Linker.Tests.Cases/RequiresCapability/RequiresCapability.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
@@ -748,9 +748,13 @@ public static void GenericTypeWithStaticMethodViaLdftn ()
 				var _ = new Action (GenericWithStaticMethod<TestType>.GenericTypeWithStaticMethodWhichRequires);
 			}
 
+			static T MakeNew<T> () where T : new() => new T ();
+			static T MakeNew2<T> () where T : new() => MakeNew<T> ();
+
 			public static void Test ()
 			{
 				GenericTypeWithStaticMethodViaLdftn ();
+				MakeNew2<TestType> ();
 			}
 		}