Assert that an added file loaded without error

Author: hamishknight

include/swift/AST/FileUnit.h

@@ -384,6 +384,9 @@ class LoadedFile : public FileUnit {
 
   virtual bool isSystemModule() const { return false; }
 
+  /// Checks whether an error was encountered while loading the file.
+  virtual bool hadLoadError() const { return false; }
+
   /// Retrieve the set of generic signatures stored within this module.
   ///
   /// \returns \c true if this module file supports retrieving all of the

include/swift/Serialization/SerializedModuleLoader.h

@@ -322,6 +322,8 @@ class SerializedASTFile final : public LoadedFile {
   /// file.
   const version::Version &getLanguageVersionBuiltWith() const;
 
+  virtual bool hadLoadError() const override;
+
   virtual bool isSystemModule() const override;
 
   virtual void lookupValue(DeclName name, NLKind lookupKind,

lib/AST/Module.cpp

@@ -498,6 +498,10 @@ bool ModuleDecl::isClangModule() const {
 }
 
 void ModuleDecl::addFile(FileUnit &newFile) {
+  // If this is a LoadedFile, make sure it loaded without error.
+  assert(!(isa<LoadedFile>(newFile) &&
+           cast<LoadedFile>(newFile).hadLoadError()));
+
   // Require Main and REPL files to be the first file added.
   assert(Files.empty() ||
          !isa<SourceFile>(newFile) ||

lib/Serialization/SerializedModuleLoader.cpp

@@ -1103,6 +1103,10 @@ bool SerializedASTFile::isSIB() const {
   return File.IsSIB;
 }
 
+bool SerializedASTFile::hadLoadError() const {
+  return File.hasError();
+}
+
 bool SerializedASTFile::isSystemModule() const {
   if (auto Mod = File.getUnderlyingModule()) {
     return Mod->isSystemModule();