Merge pull request #62251 from nkcsgexi/allowable-serialization

serialization: encode allowable client names in binary module format

include/swift/AST/Module.h

@@ -418,7 +418,19 @@ public:
     return UserModuleVersion;
   }
 
+  void addAllowableClientName(Identifier name) {
+    allowableClientNames.push_back(name);
+  }
+  ArrayRef<Identifier> getAllowableClientNames() const {
+    return allowableClientNames;
+  }
+  bool allowImportedBy(ModuleDecl *importer) const;
 private:
+
+  /// An array of module names that are allowed to import this one.
+  /// Any module can import this one if empty.
+  std::vector<Identifier> allowableClientNames;
+
   /// A cache of this module's underlying module and required bystander if it's
   /// an underscored cross-import overlay.
   Optional<std::pair<ModuleDecl *, Identifier>> declaringModuleAndBystander;