(Rosebud) Rosetta generator still produces output even without input

* This is necessary in order to set up new, empty directories of
  Rosebud input.

RPM-357

src/Rosebud/Ast.C

@@ -247,7 +247,7 @@ File::instance(const std::string &name) {
  std::ifstream test(name.c_str());
  if (!test) {
  message(FATAL, "unable to open file for reading: \"" + name + "\"");
- exit(1);
+ return {};
  } else {
  return Ptr(new File(name));
  }

src/Rosebud/rosebud.C

@@ -901,9 +901,12 @@ parseClassDefinition(const Ast::File::Ptr &file, Ast::CppStack::Stack &runningCp
  return c;
 }
 
-static void
-parseFile(const Ast::File::Ptr &file) {
- ASSERT_not_null(file);
+static Ast::File::Ptr
+parseFile(const std::string &fileName) {
+ auto file = Ast::File::instance(fileName);
+ if (!file)
+ return {};
+
  size_t filePos = 0;
  Ast::CppStack::Stack runningCppStack;
  std::vector<Token> nestingStack;
@@ -937,6 +940,8 @@ parseFile(const Ast::File::Ptr &file) {
  // Warn about file problems
  if (file->classes.empty())
  message(WARN, file, "file contains to class definitions");
+
+ return file;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -958,9 +963,8 @@ int main(int argc, char *argv[]) {
  // Parse the input files to produce the AST
  auto project = Ast::Project::instance();
  for (const std::string &arg: args) {
- auto file = Ast::File::instance(arg);
- project->files.push_back(file);
- parseFile(file);
+ if (auto file = parseFile(arg))
+ project->files.push_back(file);
  }
 
  // Additional warnings that we can't check until all the files are parsed