Swift: replace friend in TrapLabel with unsafeCreateFromExplicitId

Author: redsun82

swift/extractor/trap/TrapArena.h

@@ -16,7 +16,7 @@ class TrapArena {
  public:
   template <typename Tag>
   TrapLabel<Tag> allocateLabel() {
-    return {id_++};
+    return TrapLabel<Tag>::unsafeCreateFromExplicitId(id_++);
   }
 };
 

swift/extractor/trap/TrapLabel.h

@@ -34,16 +34,14 @@ class TrapLabel : public UntypedTrapLabel {
 
   using UntypedTrapLabel::UntypedTrapLabel;
 
-  // we want one authority tasked with creating labels to avoid conflicts, having access to the
-  // private constructor
-  // this is the TrapArena class for the moment
-  friend class TrapArena;
-
  public:
   using Tag = TagParam;
 
   TrapLabel() = default;
 
+  // The caller is responsible for ensuring ID uniqueness.
+  static TrapLabel unsafeCreateFromExplicitId(uint64_t id) { return {id}; }
+
   template <typename OtherTag>
   TrapLabel(const TrapLabel<OtherTag>& other) : UntypedTrapLabel(other) {
     // we temporarily need to bypass the label type system for unknown AST nodes and types