debug/assert: add warn_return

debug/assert.hpp

@@ -13,6 +13,8 @@
 //#include "maths.hpp" // XXX: See notes at the end of file for maths.hpp inclusion
 #include "debugger.hpp"
 
+#include <utility>
+
 
 ///////////////////////////////////////////////////////////////////////////////
 // it is fractionally easier to define a constexpr variable which can be used
@@ -389,6 +391,17 @@ void warn (std::string_view);
 void warn (const char *);
 
 
+template <typename ValueT>
+decltype(auto)
+warn_return (
+    char const *message,
+    ValueT &&value
+) {
+    warn (message);
+    return std::forward<ValueT> (value);
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 // XXX: maths needs to be included so that CHECK_EQ/NEQ can call almost_equal,
 // but maths.hpp might be using CHECK_ macros so we must include maths.hpp