AST: Introduce and adopt Decl::isExposedToClients().

This method is a more ergonomic utility wrapping DeclExportabilityVisitor.

Author: tshortli

include/swift/AST/Decl.h

@@ -957,6 +957,10 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
   unsigned getAttachedMacroDiscriminator(DeclBaseName macroName, MacroRole role,
                                          const CustomAttr *attr) const;
 
+  /// Determines if this declaration is exposed to clients of the module it is
+  /// defined in. For example, `public` declarations are exposed to clients.
+  bool isExposedToClients() const;
+
   /// Returns the innermost enclosing decl with an availability annotation.
   const Decl *getInnermostDeclWithAvailability() const;
 

lib/AST/Decl.cpp

@@ -23,6 +23,7 @@
 #include "swift/AST/AccessScope.h"
 #include "swift/AST/Attr.h"
 #include "swift/AST/CaptureInfo.h"
+#include "swift/AST/DeclExportabilityVisitor.h"
 #include "swift/AST/DiagnosticEngine.h"
 #include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/ExistentialLayout.h"
@@ -492,6 +493,10 @@ unsigned Decl::getAttachedMacroDiscriminator(DeclBaseName macroName,
       macroName);
 }
 
+bool Decl::isExposedToClients() const {
+  return DeclExportabilityVisitor().visit(this);
+}
+
 const Decl *Decl::getInnermostDeclWithAvailability() const {
   if (getAttrs().hasAttribute<AvailableAttr>())
     return this;

lib/Serialization/Serialization.cpp

@@ -16,7 +16,6 @@
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/ASTVisitor.h"
 #include "swift/AST/AutoDiff.h"
-#include "swift/AST/DeclExportabilityVisitor.h"
 #include "swift/AST/DiagnosticsCommon.h"
 #include "swift/AST/Expr.h"
 #include "swift/AST/FileSystem.h"
@@ -3306,7 +3305,7 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
   /// it, but at the same time keep the safety checks precise to avoid
   /// XRef errors and such.
   static bool isDeserializationSafe(const Decl *decl) {
-    return DeclExportabilityVisitor().visit(decl);
+    return decl->isExposedToClients();
   }
 
 private: