ENH: add refCast variant with an index to convey the context

- can be helpful, for example, when the refCast has been used on a
  boundary patch. Knowing which patch index triggered the problem
  helps with isolating the issue.

src/OpenFOAM/db/typeInfo/typeInfo.H

@@ -145,6 +145,30 @@ inline To& refCast(From& r)
 }
 
 
+//- Reference type cast template function.
+//  As per dynamicCast, but handles type names for the error messages
+//  via the virtual type() method.
+//  Can use index to convey the context.
+template<class To, class From>
+inline To& refCast(From& r, const label index)
+{
+    try
+    {
+        return dynamic_cast<To&>(r);
+    }
+    catch (const std::bad_cast&)
+    {
+        FatalErrorInFunction
+            << "Attempt to cast type " << r.type()
+            << " to type " << To::typeName
+            << " at index " << index
+            << abort(FatalError);
+
+        return dynamic_cast<To&>(r);
+    }
+}
+
+
 //- Reference type cast template function.
 //  As per dynamicCast, but handles type names for the error messages
 //  via the virtual type() method.

src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/wallFunctions/nutWallFunctions/nutWallFunction/nutWallFunctionFvPatchScalarField.C

@@ -188,7 +188,8 @@ Foam::nutWallFunctionFvPatchScalarField::nutw
     return
         refCast<const nutWallFunctionFvPatchScalarField>
         (
-            turbModel.nut()().boundaryField()[patchi]
+            turbModel.nut()().boundaryField()[patchi],
+            patchi
         );
 }