Teach the Mach-O-based AST importer to accept bare serialized ASTs.

This necessitated adding a new function to validate a serialized AST, so
that we can get the same information that used to be extracted from the
section header.

For now, we'll continue accepting the wrapped ASTs as well, since we
haven't changed the existing debug info generator.

Swift SVN r12922

include/swift/Serialization/SerializedModuleLoader.h

@@ -21,6 +21,25 @@
 namespace swift {
 class ModuleFile;
 
+/// Describes whether a loaded module can be used.
+enum class ModuleStatus {
+  /// The module is valid.
+  Valid,
+
+  /// The module file format is too new to be used by this version of the
+  /// compiler.
+  FormatTooNew,
+
+  /// The module file depends on another module that can't be loaded.
+  MissingDependency,
+
+  /// The module file is an overlay for a Clang module, which can't be found.
+  MissingShadowedModule,
+
+  /// The module file is malformed in some way.
+  Malformed
+};
+
 /// \brief Imports serialized Swift modules into an ASTContext.
 class SerializedModuleLoader : public ModuleLoader {
 private:
@@ -59,9 +78,6 @@ public:
   loadModule(SourceLoc importLoc,
              ArrayRef<std::pair<Identifier, SourceLoc>> path) override;
 
-  /// Returns true if the memory buffer contains a serialized AST.
-  static bool isValidSerializedAST(const llvm::MemoryBuffer &input);
-
   /// Attempt to load a serialized AST into the given module.
   ///
   /// If the AST cannot be loaded and \p diagLoc is present, a diagnostic is
@@ -84,28 +100,31 @@ public:
 
   virtual void loadDeclsConformingTo(KnownProtocolKind kind,
                                      unsigned previousGeneration) override;
+
+
+  /// Returns true if the data looks like it contains a serialized AST.
+  static bool isSerializedAST(StringRef data);
+
+  /// \see validateSerializedAST()
+  struct ValidationInfo {
+    StringRef name;
+    size_t bytes;
+    ModuleStatus status;
+  };
+
+  /// Returns info about the serialized AST in the given data.
+  ///
+  /// If the returned status is anything but ModuleStatus::Valid, the
+  /// serialized data cannot be loaded by this version of the compiler. If the
+  /// returned size is non-zero, it's possible to skip over this module's data,
+  /// in case there is more data in the buffer. The returned name, which may
+  /// be empty, directly points into the given data buffer.
+  ///
+  /// Note that this does not actually try to load the module or validate any
+  /// of its dependencies; it only checks that it /can/ be loaded.
+  static ValidationInfo validateSerializedAST(StringRef data);
 };
 
-/// Describes whether a loaded module can be used.
-enum class ModuleStatus {
-  /// The module is valid.
-  Valid,
-
-  /// The module file format is too new to be used by this version of the
-  /// compiler.
-  FormatTooNew,
-
-  /// The module file depends on another module that can't be loaded.
-  MissingDependency,
-
-  /// The module file is an overlay for a Clang module, which can't be found.
-  MissingShadowedModule,
-
-  /// The module file is malformed in some way.
-  Malformed
-};
-
-
 /// A file-unit loaded from a serialized AST file.
 class SerializedASTFile final : public LoadedFile {
   friend class SerializedModuleLoader;