Introduce "SourceFile" within a TranslationUnit.

Right now this is just an extra layer of indirection for the decls,
operators, and imports in a TU, but it's the first step towards compiling
multiple source files at once without pretending they're all in a single
file. This is important for the "implicit visibility" feature, where
declarations from other source files in the same module are accessible
from the file currently being compiled.

Swift SVN r9072

include/swift/AST/Module.h

@@ -54,6 +54,7 @@ namespace swift {
   class ProtocolConformance;
   class ProtocolDecl;
   struct PrintOptions;
+  class TranslationUnit;
   class TupleType;
   class Type;
   class ValueDecl;
@@ -360,19 +361,14 @@ public:
   void *operator new(size_t Bytes, ASTContext &C,
                      unsigned Alignment = alignof(Module));
 };
-  
-/// TranslationUnit - This contains information about all of the decls and
-/// external references in a translation unit, which is one file.
-class TranslationUnit : public Module {
-private:
+
+
+class SourceFile {
   /// This is the list of modules that are imported by this module, with the
   /// second element of the pair declaring whether the module is reexported.
   ///
   /// This is filled in by the Name Binding phase.
-  ArrayRef<std::pair<ImportedModule, bool>> Imports;
-
-  /// The list of libraries specified as link-time dependencies at compile time.
-  ArrayRef<LinkLibrary> LinkLibraries;
+  ArrayRef<std::pair<Module::ImportedModule, bool>> Imports;
 
   /// \brief The buffer ID for the file that was imported as this TU, or -1
   /// if this TU is not an imported TU.
@@ -383,22 +379,12 @@ private:
   ExternalNameLookup *ExternalLookup = nullptr;
 
 public:
-  /// Kind - This is the sort of file the translation unit was parsed for, which
-  /// can affect some type checking and other behavior.
-  enum TUKind {
-    Library,
-    Main,
-    REPL,
-    SIL       // Came from a .sil file.
-  } Kind;
+  /// The translation unit that this file is a part of.
+  TranslationUnit &TU;
 
-  /// If this is true, then the translation unit is allowed to access the
-  /// Builtin module with an explicit import.
-  bool HasBuiltinModuleAccess = false;
-  
   /// The list of top-level declarations for a translation unit.
   std::vector<Decl*> Decls;
-  
+
   /// A map of operator names to InfixOperatorDecls.
   /// Populated during name binding; the mapping will be incomplete until name
   /// binding is complete.
@@ -414,18 +400,54 @@ public:
   /// binding is complete.
   llvm::StringMap<PrefixOperatorDecl*> PrefixOperators;
 
-  TranslationUnit(Identifier Name, Component *Comp, ASTContext &C, TUKind Kind)
-    : Module(ModuleKind::TranslationUnit, Name, Comp, C), Kind(Kind) {
-  }
-  
-  ArrayRef<std::pair<ImportedModule, bool>> getImports() const {
-    assert(ASTStage >= Parsed || Kind == SIL);
+  SourceFile(TranslationUnit &tu) : TU(tu) {}
+
+  ArrayRef<std::pair<Module::ImportedModule, bool>> getImports() const {
     return Imports;
   }
-  void setImports(ArrayRef<std::pair<ImportedModule, bool>> IM) {
+  void setImports(ArrayRef<std::pair<Module::ImportedModule, bool>> IM) {
     Imports = IM;
   }
 
+  /// \brief The buffer ID for the file that was imported as this TU, or -1
+  /// if this is not an imported TU.
+  int getImportBufferID() const { return ImportBufferID; }
+  void setImportBufferID(unsigned BufID) {
+    assert(ImportBufferID == -1 && "Already set!");
+    ImportBufferID = BufID;
+  }
+};
+
+  
+/// TranslationUnit - This contains information about all of the decls and
+/// external references in a translation unit, which is one file.
+class TranslationUnit : public Module {
+private:
+  /// The list of libraries specified as link-time dependencies at compile time.
+  ArrayRef<LinkLibrary> LinkLibraries;
+
+public:
+  // FIXME: Make private.
+  std::unique_ptr<SourceFile> MainSourceFile;
+
+  /// Kind - This is the sort of file the translation unit was parsed for, which
+  /// can affect some type checking and other behavior.
+  enum TUKind {
+    Library,
+    Main,
+    REPL,
+    SIL       // Came from a .sil file.
+  } Kind;
+
+  /// If this is true, then the translation unit is allowed to access the
+  /// Builtin module with an explicit import.
+  bool HasBuiltinModuleAccess = false;
+
+  TranslationUnit(Identifier Name, Component *Comp, ASTContext &C, TUKind Kind)
+    : Module(ModuleKind::TranslationUnit, Name, Comp, C),
+      MainSourceFile(new SourceFile(*this)), Kind(Kind) {
+  }
+  
   void setLinkLibraries(ArrayRef<LinkLibrary> libs) {
     assert(LinkLibraries.empty() && "link libraries already set");
     LinkLibraries = libs;
@@ -439,6 +461,7 @@ public:
   void cacheVisibleDecls(SmallVectorImpl<ValueDecl *> &&globals) const;
   const SmallVectorImpl<ValueDecl *> &getCachedVisibleDecls() const;
 
+<<<<<<< HEAD
   /// \brief The buffer ID for the file that was imported as this TU, or -1
   /// if this is not an imported TU.
   int getImportBufferID() const { return ImportBufferID; }
@@ -453,6 +476,8 @@ public:
     ExternalLookup = R;
   }
 
+=======
+>>>>>>> 57085cf... Introduce "SourceFile" within a TranslationUnit.
   /// \returns true if traversal was aborted, false otherwise.
   bool walk(ASTWalker &Walker);
 
@@ -480,7 +505,6 @@ public:
   }
 };
 
-  
 /// BuiltinModule - This module represents the compiler's implicitly generated
 /// declarations in the builtin module.
 class BuiltinModule : public Module {