Error if no input file given

src/fart/main.cpp

@@ -10,6 +10,11 @@ int main(int argc, char * argv[])
     {
         return rc - 1;
     }
+    if (cli.input_file.empty())
+    {
+        fprintf(stderr, "Error: no input file specified\n");
+        return 1;
+    }
     Engine engine(cli.params);
     return engine.run(cli.input_file, cli.output_file);
 }