[NFC] Attach SynthesizedFile to any FileUnit

Gives us a place to stuff synthesized declarations for, among other things, imported Clang decls.

include/swift/AST/FileUnit.h

@@ -17,7 +17,11 @@
 #include "swift/AST/RawComment.h"
 #include "swift/Basic/BasicSourceInfo.h"
 
+#include "llvm/ADT/PointerIntPair.h"
+
 namespace swift {
+class SynthesizedFileUnit;
+
 /// A container for module-scope declarations that itself provides a scope; the
 /// smallest unit of code organization.
 ///
@@ -33,19 +37,25 @@ class FileUnit : public DeclContext, public ASTAllocated<FileUnit> {
   friend class DirectOperatorLookupRequest;
   friend class DirectPrecedenceGroupLookupRequest;
 
-  // FIXME: Stick this in a PointerIntPair.
-  const FileUnitKind Kind;
+  // The pointer is FileUnit insted of SynthesizedFileUnit to break circularity.
+  llvm::PointerIntPair<FileUnit *, 3, FileUnitKind> SynthesizedFileAndKind;
 
 protected:
   FileUnit(FileUnitKind kind, ModuleDecl &M)
-    : DeclContext(DeclContextKind::FileUnit, &M), Kind(kind) {
+    : DeclContext(DeclContextKind::FileUnit, &M),
+      SynthesizedFileAndKind(nullptr, kind) {
   }
 
 public:
   FileUnitKind getKind() const {
-    return Kind;
+    return SynthesizedFileAndKind.getInt();
   }
 
+  /// Returns the synthesized file for this source file, if it exists.
+  SynthesizedFileUnit *getSynthesizedFile() const;
+
+  SynthesizedFileUnit &getOrCreateSynthesizedFile();
+
   /// Look up a (possibly overloaded) value set at top-level scope
   /// (but with the specified access path, which may come from an import decl)
   /// within this file.

include/swift/AST/SourceFile.h

@@ -89,9 +89,6 @@ private:
   /// same module.
   mutable Identifier PrivateDiscriminator;
 
-  /// A synthesized file corresponding to this file, created on-demand.
-  SynthesizedFileUnit *SynthesizedFile = nullptr;
-
   /// The root TypeRefinementContext for this SourceFile.
   ///
   /// This is set during type checking.
@@ -409,11 +406,6 @@ public:
   Optional<ExternalSourceLocs::RawLocs>
   getExternalRawLocsForDecl(const Decl *D) const override;
 
-  /// Returns the synthesized file for this source file, if it exists.
-  SynthesizedFileUnit *getSynthesizedFile() const { return SynthesizedFile; };
-
-  SynthesizedFileUnit &getOrCreateSynthesizedFile();
-
   virtual bool walk(ASTWalker &walker) override;
 
   /// The buffer ID for the file that was imported, or None if there

include/swift/AST/SynthesizedFileUnit.h

@@ -18,14 +18,12 @@
 
 namespace swift {
 
-class SourceFile;
-
 /// A container for synthesized declarations, attached to a `SourceFile`.
 ///
 /// Currently, only module-level synthesized declarations are supported.
 class SynthesizedFileUnit final : public FileUnit {
   /// The parent source file.
-  SourceFile &SF;
+  FileUnit &FU;
 
   /// Synthesized top level declarations.
   TinyPtrVector<Decl *> TopLevelDecls;
@@ -36,11 +34,11 @@ class SynthesizedFileUnit final : public FileUnit {
   mutable Identifier PrivateDiscriminator;
 
 public:
-  SynthesizedFileUnit(SourceFile &SF);
+  SynthesizedFileUnit(FileUnit &FU);
   ~SynthesizedFileUnit() = default;
 
   /// Returns the parent source file.
-  SourceFile &getSourceFile() const { return SF; }
+  FileUnit &getFileUnit() const { return FU; }
 
   /// Add a synthesized top-level declaration.
   void addTopLevelDecl(Decl *D) { TopLevelDecls.push_back(D); }

lib/AST/Module.cpp

@@ -2857,7 +2857,8 @@ ASTScope &SourceFile::getScope() {
 
 Identifier
 SourceFile::getDiscriminatorForPrivateValue(const ValueDecl *D) const {
-  assert(D->getDeclContext()->getModuleScopeContext() == this);
+  assert(D->getDeclContext()->getModuleScopeContext() == this ||
+         D->getDeclContext()->getModuleScopeContext() == getSynthesizedFile());
 
   if (!PrivateDiscriminator.empty())
     return PrivateDiscriminator;
@@ -2896,11 +2897,19 @@ SourceFile::getDiscriminatorForPrivateValue(const ValueDecl *D) const {
   return PrivateDiscriminator;
 }
 
-SynthesizedFileUnit &SourceFile::getOrCreateSynthesizedFile() {
-  if (SynthesizedFile)
-    return *SynthesizedFile;
+SynthesizedFileUnit *FileUnit::getSynthesizedFile() const {
+  return cast_or_null<SynthesizedFileUnit>(SynthesizedFileAndKind.getPointer());
+}
+
+SynthesizedFileUnit &FileUnit::getOrCreateSynthesizedFile() {
+  auto SynthesizedFile = getSynthesizedFile();
+  if (!SynthesizedFile) {
+    if (auto thisSynth = dyn_cast<SynthesizedFileUnit>(this))
+      return *thisSynth;
     SynthesizedFile = new (getASTContext()) SynthesizedFileUnit(*this);
+    SynthesizedFileAndKind.setPointer(SynthesizedFile);
     getParentModule()->addFile(*SynthesizedFile);
+  }
   return *SynthesizedFile;
 }
 
@@ -2950,9 +2959,9 @@ SourceFile::lookupOpaqueResultType(StringRef MangledName) {
 // SynthesizedFileUnit Implementation
 //===----------------------------------------------------------------------===//
 
-SynthesizedFileUnit::SynthesizedFileUnit(SourceFile &SF)
-    : FileUnit(FileUnitKind::Synthesized, *SF.getParentModule()), SF(SF) {
-  SF.getASTContext().addDestructorCleanup(*this);
+SynthesizedFileUnit::SynthesizedFileUnit(FileUnit &FU)
+    : FileUnit(FileUnitKind::Synthesized, *FU.getParentModule()), FU(FU) {
+  FU.getASTContext().addDestructorCleanup(*this);
 }
 
 Identifier
@@ -2963,23 +2972,15 @@ SynthesizedFileUnit::getDiscriminatorForPrivateValue(const ValueDecl *D) const {
   if (!PrivateDiscriminator.empty())
     return PrivateDiscriminator;
 
-  StringRef sourceFileName = getSourceFile().getFilename();
-  if (sourceFileName.empty()) {
-    assert(1 == count_if(getParentModule()->getFiles(),
-                         [](const FileUnit *FU) -> bool {
-                           return isa<SourceFile>(FU) &&
-                                  cast<SourceFile>(FU)->getFilename().empty();
-                         }) &&
-           "Cannot promise uniqueness if multiple source files are nameless");
-  }
+  // Start with the discriminator that the file we belong to would use.
+  auto ownerDiscriminator = getFileUnit().getDiscriminatorForPrivateValue(D);
 
-  // Use a discriminator invariant across Swift version: a hash of the module
-  // name, the parent source file name, and a special string.
-  llvm::MD5 hash;
-  hash.update(getParentModule()->getName().str());
-  hash.update(llvm::sys::path::filename(sourceFileName));
+  // Hash that with a special string to produce a different value that preserves
+  // the entropy of the original.
   // TODO: Use a more robust discriminator for synthesized files. Pick something
   // that cannot conflict with `SourceFile` discriminators.
+  llvm::MD5 hash;
+  hash.update(ownerDiscriminator.str());
   hash.update("SYNTHESIZED FILE");
   llvm::MD5::MD5Result result;
   hash.final(result);

lib/IRGen/IRGenRequests.cpp

@@ -68,10 +68,9 @@ TinyPtrVector<FileUnit *> IRGenDescriptor::getFilesToEmit() const {
   TinyPtrVector<FileUnit *> files;
   files.push_back(primary);
 
-  if (auto *SF = dyn_cast<SourceFile>(primary)) {
-    if (auto *synthesizedFile = SF->getSynthesizedFile())
+  if (auto *synthesizedFile = primary->getSynthesizedFile())
     files.push_back(synthesizedFile);
-  }
+
   return files;
 }
 

lib/Sema/TypeCheckConcurrency.cpp

@@ -3946,8 +3946,8 @@ NormalProtocolConformance *GetImplicitSendableRequest::evaluate(
       nominal->addExtension(extension);
 
       // Make it accessible to getTopLevelDecls()
-      if (auto sf = dyn_cast<SourceFile>(nominal->getModuleScopeContext()))
-        sf->getOrCreateSynthesizedFile().addTopLevelDecl(extension);
+      if (auto file = dyn_cast<FileUnit>(nominal->getModuleScopeContext()))
+        file->getOrCreateSynthesizedFile().addTopLevelDecl(extension);
 
       conformanceDC = extension;
     }

lib/TBDGen/TBDGen.cpp

@@ -1203,10 +1203,8 @@ void TBDGenVisitor::visit(const TBDGenDescriptor &desc) {
     visitFile(singleFile);
 
     // Visit synthesized file, if it exists.
-    if (auto *SF = dyn_cast<SourceFile>(singleFile)) {
-      if (auto *synthesizedFile = SF->getSynthesizedFile())
+    if (auto *synthesizedFile = singleFile->getSynthesizedFile())
       visitFile(synthesizedFile);
-    }
     return;
   }