Sink private-file import support down to SerializedASTFile

Implementing it in LoadedFile is nice in theory, but causes a leak in
practice because that type is ASTContext-allocated and usually never
destroyed.

https://bugs.swift.org/browse/SR-11366

Author: jrose-apple

include/swift/AST/Module.h

@@ -1387,28 +1387,14 @@ class LoadedFile : public FileUnit {
     : FileUnit(Kind, M) {
     assert(classof(this) && "invalid kind");
   }
-
-  /// A map from private/fileprivate decls to the file they were defined in.
-  llvm::DenseMap<const ValueDecl *, Identifier> FilenameForPrivateDecls;
-
 public:
-
   /// Returns an arbitrary string representing the storage backing this file.
   ///
   /// This is usually a filesystem path.
   virtual StringRef getFilename() const;
 
-  void addFilenameForPrivateDecl(const ValueDecl *decl, Identifier id) {
-    assert(!FilenameForPrivateDecls.count(decl) ||
-           FilenameForPrivateDecls[decl] == id);
-    FilenameForPrivateDecls[decl] = id;
-  }
-
-  StringRef getFilenameForPrivateDecl(const ValueDecl *decl) {
-    auto it = FilenameForPrivateDecls.find(decl);
-    if (it == FilenameForPrivateDecls.end())
-      return StringRef();
-    return it->second.str();
+  virtual StringRef getFilenameForPrivateDecl(const ValueDecl *decl) const {
+    return StringRef();
   }
 
   /// Look up an operator declaration.

include/swift/Serialization/ModuleFile.h

@@ -396,6 +396,7 @@ class ModuleFile
   std::unique_ptr<SerializedObjCMethodTable> ObjCMethods;
 
   llvm::DenseMap<const ValueDecl *, Identifier> PrivateDiscriminatorsByValue;
+  llvm::DenseMap<const ValueDecl *, StringRef> FilenamesForPrivateValues;
 
   TinyPtrVector<Decl *> ImportDecls;
 

include/swift/Serialization/SerializedModuleLoader.h

@@ -274,6 +274,9 @@ class SerializedASTFile final : public LoadedFile {
                            DeclName name, NLKind lookupKind,
                            SmallVectorImpl<ValueDecl*> &results) const override;
 
+  virtual StringRef
+  getFilenameForPrivateDecl(const ValueDecl *decl) const override;
+
   virtual TypeDecl *lookupLocalType(StringRef MangledName) const override;
 
   virtual OpaqueTypeDecl *

lib/Serialization/Deserialization.cpp

@@ -2254,7 +2254,7 @@ class swift::DeclDeserializer {
 
   Identifier privateDiscriminator;
   unsigned localDiscriminator = 0;
-  Identifier filenameForPrivate;
+  StringRef filenameForPrivate;
 
   void AddAttribute(DeclAttribute *Attr) {
     // Advance the linked list.
@@ -2308,10 +2308,8 @@ class swift::DeclDeserializer {
       if (localDiscriminator != 0)
         value->setLocalDiscriminator(localDiscriminator);
 
-      if (!filenameForPrivate.empty()) {
-        auto *loadedFile = cast<LoadedFile>(MF.getFile());
-        loadedFile->addFilenameForPrivateDecl(value, filenameForPrivate);
-      }
+      if (!filenameForPrivate.empty())
+        MF.FilenamesForPrivateValues[value] = filenameForPrivate;
     }
 
     decl->setValidationToChecked();
@@ -4202,7 +4200,7 @@ llvm::Error DeclDeserializer::deserializeDeclAttributes() {
     } else if (recordID == decls_block::FILENAME_FOR_PRIVATE) {
       IdentifierID filenameID;
       decls_block::FilenameForPrivateLayout::readRecord(scratch, filenameID);
-      filenameForPrivate = MF.getIdentifier(filenameID);
+      filenameForPrivate = MF.getIdentifierText(filenameID);
     } else {
       return llvm::Error::success();
     }

lib/Serialization/SerializedModuleLoader.cpp

@@ -955,6 +955,11 @@ void SerializedASTFile::lookupValue(ModuleDecl::AccessPathTy accessPath,
   File.lookupValue(name, results);
 }
 
+StringRef
+SerializedASTFile::getFilenameForPrivateDecl(const ValueDecl *decl) const {
+  return File.FilenamesForPrivateValues.lookup(decl);
+}
+
 TypeDecl *SerializedASTFile::lookupLocalType(llvm::StringRef MangledName) const{
   return File.lookupLocalType(MangledName);
 }