feat: overloads with static_assert added to improve migration

src/core/include/mp-units/framework/quantity.h

@@ -166,6 +166,14 @@ public:
   {
   }
 
+  template<typename Value, Reference R2>
+    requires(!DeltaReference<R2>)
+  constexpr quantity(Value&&, R2)
+  {
+    static_assert(false,
+                  "References using offset units (e.g., temperatures) must be explicitly qualified with `delta`");
+  }
+
   template<detail::QuantityConvertibleTo<quantity> Q>
   // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
   constexpr explicit(!std::convertible_to<typename Q::rep, Rep>) quantity(const Q& q) :
@@ -433,6 +441,11 @@ template<typename Value, DeltaReference R>
   requires RepresentationOf<Value, get_quantity_spec(detail::get_original_reference(R{})).character>
 quantity(Value v, R) -> quantity<detail::get_original_reference(R{}), Value>;
 
+// the below is needed only to fire static_asserts in the constructor
+template<typename Value, Reference R>
+  requires(!DeltaReference<R>) && RepresentationOf<Value, get_quantity_spec(R{}).character>
+quantity(Value v, R) -> quantity<R{}, Value>;
+
 template<QuantityLike Q>
 explicit(
   is_specialization_of<decltype(quantity_like_traits<Q>::to_numerical_value(std::declval<Q>())), convert_explicitly>)

src/core/include/mp-units/framework/reference.h

@@ -219,6 +219,24 @@ operator/(Rep&& lhs, R)
   return quantity_point{std::forward<Rep>(lhs) * delta<inverse(detail::get_original_reference(R{}))>};
 }
 
+template<typename Rep, Reference R>
+  requires(!DeltaReference<R>) && RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R{}).character>
+[[noreturn]] constexpr auto operator*(Rep&&, R)
+{
+  static_assert(
+    false,
+    "References using offset units (e.g., temperatures) must be explicitly qualified with `delta` or `absolute`");
+}
+
+template<typename Rep, Reference R>
+  requires(!DeltaReference<R>) && RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R{}).character>
+[[noreturn]] constexpr auto operator/(Rep&&, R)
+{
+  static_assert(
+    false,
+    "References using offset units (e.g., temperatures) must be explicitly qualified with `delta` or `absolute`");
+}
+
 template<Reference R, typename Rep>
   requires RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R{}).character>
 // NOLINTNEXTLINE(cppcoreguidelines-missing-std-forward)