Lazy initialize Swift runtime in backwards interop synth provider

[adrian-prantl]

Otherwise the Swift runtime and scratch context will be initialized in
any process that contains C++ struct types, which costs performance
and produces spurious warnings if no Swift runtime is available.

rdar://116533409

[adrian-prantl]

@swift-ci test

[augusto2112]

Do you think you could change this loop to fid the swift_name instead, and get the type system after the loop, only if you found a name? This way you don't need to have TypeSystemSwift *ts = nullptr; and setting it inside the statement.

[adrian-prantl]

Sure.

[augusto2112]

An alternative implementation would be to extract the part that finds the swift name into it's own function:

static StringRef FindSwiftMangledNameFromCxxInteropType(CompilerType type) {
  Log *log(GetLog(LLDBLog::DataFormatters));
  // This only makes sense for Clang types.
  auto tsc = type.GetTypeSystem().dyn_cast_or_null<TypeSystemClang>();
  if (!tsc)
    return {};

  // We operate directly on the qualified type because the TypeSystem
  // interface doesn't allow us to check for static constexpr members.
  auto qual_type = TypeSystemClang::GetQualType(type.GetOpaqueQualType());
  auto *record_type =
      llvm::dyn_cast_or_null<clang::RecordType>(qual_type.getTypePtrOrNull());
  if (!record_type) {
    LLDB_LOGV(log, "[ExtractSwiftTypeFromCxxInteropType] "
                   "Type is not a record type.");
    return {};
  }

  const clang::RecordDecl *record_decl = record_type->getDecl();
  CompilerType swift_type;

  for (auto *child_decl : record_decl->decls()) {
    auto *var_decl = llvm::dyn_cast<clang::VarDecl>(child_decl);
    if (!var_decl)
      continue;

    auto name = var_decl->getName();
    if (name != "__swift_mangled_name")
      continue;

    const auto *typedef_type =
        llvm::dyn_cast<clang::TypedefType>(var_decl->getType());
    if (!typedef_type)
      break;

    auto *decl = typedef_type->getDecl();
    if (!decl)
      break;

    auto swift_name = decl->getName();
    if (!swift::Demangle::isMangledName(swift_name))
      break;

    return swift_name;
  }

  return {};
}

And have ExtractSwiftTypeFromCxxInteropType take in the swift name as well.

This way, you can check for the swift name in the beginning of the formatter closure:

    g_formatters.push_back([](lldb_private::ValueObject &valobj,
                              lldb::DynamicValueType dyn_type,
                              FormatManager &format_manager)
                               -> lldb::SyntheticChildrenSP {
      Log *log(GetLog(LLDBLog::DataFormatters));

      auto type = valobj.GetCompilerType();
      auto swift_name = FindSwiftMangledNameFromCxxInteropType(type);
      if (swift_name.empty())
        return nullptr;
      // If there's a swift name, it's safe to get the swift scratch context.

And no need to pass in closures to the extract function.

I think breaking ExtractSwiftTypeFromCxxInteropType into two functions would be a nice change, and not passing in functions to lazily initialize the scratch context makes things slightly simpler. What do you think?

[adrian-prantl]

How would that work for the recursive case?

[adrian-prantl]

@swift-ci test

[augusto2112]

How would that work for the recursive case?

You just call the other function in the closure:

    auto bound_type = runtime.BindGenericTypeParameters(
        swift_type, [&](unsigned depth, unsigned index) -> CompilerType {
          assert(depth == 0 && "Unexpected depth! C++ interop does not support "
                               "nested generic parameters");
          if (depth > 0)
            return {};

          auto templated_type = type.GetTypeTemplateArgument(index);
          auto templated_type_name = FindSwiftMangledNameFromCxxInteropType(templated_type);
          auto substituted_type =
              ExtractSwiftTypeFromCxxInteropType(templated_type, templated_type_name, ts, runtime);
          ...

[adrian-prantl]

Done.

[adrian-prantl]

@swift-ci test

[adrian-prantl]

@swift-ci test windows

[adrian-prantl]

@swift-ci test windows