[NF] Relax variability error in functions

The binding expression of a parameter in a function is now allowed to be
a discrete expression (since we do not distinguish between inputs and
other bindings). This now gives a warning instead of an error (because
the Modelica specification does not seem to allow this, but other tools
and libraries use this pattern for no obvious reason).

Belonging to [master]:
  - OpenModelica/OMCompiler#2321

Compiler/NFFrontEnd/NFTyping.mo

@@ -621,11 +621,16 @@ algorithm
           comp_var := Component.variability(c);
 
           if Binding.variability(binding) > comp_var then
-            Error.addSourceMessage(Error.HIGHER_VARIABILITY_BINDING,
-              {name, Prefixes.variabilityString(Component.variability(c)),
-               "'" + Binding.toString(c.binding) + "'", Prefixes.variabilityString(Binding.variability(binding))},
-              Binding.getInfo(binding));
-            fail();
+            if comp_var == Variability.PARAMETER and intBitAnd(origin, ExpOrigin.FUNCTION) > 0 then
+              Error.addSourceMessage(Error.FUNCTION_HIGHER_VARIABILITY_BINDING, {name, Prefixes.variabilityString(Component.variability(c)),
+                 "'" + Binding.toString(c.binding) + "'", Prefixes.variabilityString(Binding.variability(binding))}, Binding.getInfo(binding));
+            else
+              Error.addSourceMessage(Error.HIGHER_VARIABILITY_BINDING,
+                {name, Prefixes.variabilityString(Component.variability(c)),
+                 "'" + Binding.toString(c.binding) + "'", Prefixes.variabilityString(Binding.variability(binding))},
+                Binding.getInfo(binding));
+              fail();
+            end if;
           end if;
 
           // Evaluate the binding if the component is a constant.

Compiler/Util/Error.mo

@@ -963,6 +963,8 @@ public constant Message NON_STATE_STATESELECT_ALWAYS = MESSAGE(591, SYMBOLIC(),
   Util.gettext("Variable %s has attribute stateSelect=StateSelect.always, but was selected as a continuous variable."));
 public constant Message STATE_STATESELECT_NEVER = MESSAGE(592, SYMBOLIC(), WARNING(),
   Util.gettext("Variable %s has attribute stateSelect=StateSelect.never, but was selected as a state"));
+public constant Message FUNCTION_HIGHER_VARIABILITY_BINDING = MESSAGE(593, TRANSLATION(), WARNING(),
+  Util.gettext("Component ‘%s’ of variability %s has binding %s of higher variability %s."));
 
 public constant Message MATCH_SHADOWING = MESSAGE(5001, TRANSLATION(), ERROR(),
   Util.gettext("Local variable '%s' shadows another variable."));