Allow cold values in static methods using parametricity

Closes #14460

Allow cold arguments to be passed if the parameter is `!Matchable` and the method is global static.

Author: Xavientois

compiler/src/dotty/tools/dotc/transform/init/Semantic.scala

@@ -1120,7 +1120,14 @@ object Semantic {
 
       case Call(ref, argss) =>
         // check args
-        val (errors, args) = evalArgs(argss.flatten, thisV, klass)
+        val (argErrors, args) = evalArgs(argss.flatten, thisV, klass)
+        // Allow cold args for static methods with non-matchable params
+        val methodType = ref.symbol.info.stripPoly
+        val allMatchable = methodType.paramInfoss.flatten.forall { (info) => info <:< defn.MatchableType }
+        val isStatic = ref.symbol.isStatic
+        val errors = if isStatic && allMatchable then
+          argErrors.filterNot(e => e.isInstanceOf[UnsafePromotion])
+        else argErrors
 
         ref match
         case Select(supert: Super, _) =>

tests/init/pos/inner-enum.scala

@@ -0,0 +1,4 @@
+class Outer:
+    enum MyEnum {
+        case Case
+    }