Add Decl::isPrivateToEnclosingFile

Author: David Ungar

include/swift/AST/Decl.h

@@ -920,6 +920,9 @@ class alignas(1 << DeclAlignInBits) Decl {
   /// If this returns true, the decl can be safely casted to ValueDecl.
   bool isPotentiallyOverridable() const;
 
+  /// Returns true if this Decl cannot be seen by any other source file
+  bool isPrivateToEnclosingFile() const;
+
   /// If an alternative module name is specified for this decl, e.g. using
   /// @_originalDefinedIn attribute, this function returns this module name.
   StringRef getAlternateModuleName() const;

lib/AST/Decl.cpp

@@ -8068,3 +8068,26 @@ void swift::simple_display(llvm::raw_ostream &out, AnyFunctionRef fn) {
   else
     out << "closure";
 }
+
+bool Decl::isPrivateToEnclosingFile() const {
+  if (auto *VD = dyn_cast<ValueDecl>(this))
+    return VD->getFormalAccess() <= AccessLevel::FilePrivate;
+  switch (getKind()) {
+  case DeclKind::Import:
+  case DeclKind::PatternBinding:
+  case DeclKind::EnumCase:
+  case DeclKind::TopLevelCode:
+  case DeclKind::IfConfig:
+  case DeclKind::PoundDiagnostic:
+    return true;
+
+  case DeclKind::Extension:
+  case DeclKind::InfixOperator:
+  case DeclKind::PrefixOperator:
+  case DeclKind::PostfixOperator:
+    return false;
+
+  default:
+    llvm_unreachable("everything else is a ValueDecl");
+  }
+}