Update UseExceptionThrowHelpers to only recommend ANE for classes

Author: stephentoub

src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/UseExceptionThrowHelpers.cs

@@ -180,7 +180,8 @@ aooreThrowIfGreaterThan is not null || aooreThrowIfGreaterThanOrEqual is not nul
                     if (SymbolEqualityComparer.Default.Equals(objectCreationOperation.Type, ane))
                     {
                         if (aneThrowIfNull is not null &&
-                            IsParameterNullCheck(condition.Condition, out IParameterReferenceOperation? nullCheckParameter))
+                            IsParameterNullCheck(condition.Condition, out IParameterReferenceOperation? nullCheckParameter) &&
+                            nullCheckParameter.Type.TypeKind == TypeKind.Class)
                         {
                             context.ReportDiagnostic(condition.CreateDiagnostic(
                                 UseArgumentNullExceptionThrowIfNullRule,

src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Runtime/UseExceptionThrowHelpersTests.cs

@@ -177,6 +177,24 @@ string this[string name]
             return name;
         }
     }
+
+    void NullableArg(int? arg)
+    {
+        if (arg is null) throw new ArgumentNullException(nameof(arg));
+    }
+
+    void GenericMethod<T>(T arg)
+    {
+        if (arg is null) throw new ArgumentNullException(nameof(arg));
+    }
+}
+
+class GenericType<T>
+{
+    void M(T arg)
+    {
+        if (arg is null) throw new ArgumentNullException(nameof(arg));
+    }
 }
 ",
                 FixedCode =
@@ -260,6 +278,24 @@ string this[string name]
             return name;
         }
     }
+
+    void NullableArg(int? arg)
+    {
+        if (arg is null) throw new ArgumentNullException(nameof(arg));
+    }
+
+    void GenericMethod<T>(T arg)
+    {
+        if (arg is null) throw new ArgumentNullException(nameof(arg));
+    }
+}
+
+class GenericType<T>
+{
+    void M(T arg)
+    {
+        if (arg is null) throw new ArgumentNullException(nameof(arg));
+    }
 }
 "
             }.RunAsync();