prefix module qualified names with __module__ (pytorch#23630)

Summary:
Pull Request resolved: pytorch#23630

This is temporary, won't be needed with the new serialization format.
But for now, since the main module gets its name from the archive name,
we need this for safety, other wise something like
`torch.jit.save("torch.pt") will break things.

Test Plan: Imported from OSS

Reviewed By: jamesr66a

Differential Revision: D16592404

Pulled By: suo

fbshipit-source-id: b538dc3438a80ea7bca14d84591ecd63f4b1289f

aten/src/ATen/core/qualified_name.h

@@ -35,7 +35,7 @@ struct QualifiedName {
     cacheAccessors();
   }
 
-  /* implicit */ QualifiedName(const std::vector<std::string>& atoms) {
+  explicit QualifiedName(std::vector<std::string> atoms) {
     for (const auto& atom : atoms) {
       TORCH_CHECK(!atom.empty(), "Atom cannot be empty");
       TORCH_CHECK(

torch/csrc/jit/import.cpp

@@ -305,7 +305,8 @@ script::Module ScriptModuleDeserializer::convertModule(
   for (const auto& atom : atoms) {
     moduleStack_.emplace_back(atom);
   }
-  auto module = script::Module(moduleStack_, compilation_unit_);
+  auto module =
+      script::Module(c10::QualifiedName(moduleStack_), compilation_unit_);
   for (int i = 0; i < module_def.submodules_size(); ++i) {
     const torch::ModuleDef& sub_def = module_def.submodules(i);
     auto submodule = convertModule(sub_def);

torch/csrc/jit/script/module.cpp

@@ -16,6 +16,15 @@ static ModulePtr create_module_object(
     c10::QualifiedName class_name,
     std::shared_ptr<CompilationUnit> cu,
     bool shouldMangle = false) {
+  // XXX: This is a temporary hack so that module names cannot clash with
+  // builtins like `torch`. Delete this with the new serialization format.
+  std::vector<std::string> new_class_name{"__module__"};
+  new_class_name.insert(
+      new_class_name.end(),
+      class_name.atoms().begin(),
+      class_name.atoms().end());
+  class_name = c10::QualifiedName(std::move(new_class_name));
+
   if (shouldMangle && cu->get_class(class_name) != nullptr) {
     class_name = cu->mangle(class_name);
   }