…ecord level.
This fixes the incorrect diagnostic emitted when compiling the following
snippet
```
// string_view.h
template<class _CharT>
class basic_string_view;
typedef basic_string_view<char> string_view;
template<class _CharT>
class
__attribute__((__preferred_name__(string_view)))
basic_string_view {
public:
basic_string_view()
{
}
};
inline basic_string_view<char> foo()
{
return basic_string_view<char>();
}
// A.cppm
module;
#include "string_view.h"
export module A;
// Use.cppm
module;
#include "string_view.h"
export module Use;
import A;
```
The diagnostic is
```
string_view.h:11:5: error: 'basic_string_view<char>::basic_string_view' from module 'A.<global>' is not present in definition of 'string_view' provided earlier
```
The underlying issue is that deserialization of the `preferred_name`
attribute triggers deserialization of `basic_string_view<char>`, which
triggers the deserialization of the `preferred_name` attribute again
(since it's attached to the `basic_string_view` template).
The deserialization logic is implemented in a way that prevents it from
going on a loop in a literal sense (it detects early on that it has
already seen the `string_view` typedef when trying to start its
deserialization for the second time), but leaves the typedef
deserialization in an unfinished state. Subsequently, the `string_view`
typedef from the deserialized module cannot be merged with the same
typedef from `string_view.h`, resulting in the above diagnostic.
This PR resolves the problem by delaying the deserialization of the
`preferred_name` attribute until the deserialization of the
`basic_string_view` template is completed. As a result of deferring, the
deserialization of the `preferred_name` attribute doesn't need to go on
a loop since the type of the `string_view` typedef is already known when
it's deserialized.
c3ba6f378e