[clang] Asserts in ADL when finding exported declaration in the implicit global module

[mizvekov]

Repro:

//--- A.cppm
module;
export module A;
export extern "C" void foo(struct Bar);

//--- B.cppm
module;
import A;
export module B;

//--- C.cpp
import B;
struct Bar {};
void test() {
  foo(Bar());
}

Crashes with:

Assertion failed: (FM && FM->isNamedModule() && !FM->isPrivateModule() && "bad export context"), function ArgumentDependentLookup, file SemaLookup.cpp, line 3854.

This is not just a crash on invalid. Slightly more complex, but valid, example:

//--- foo.h
struct Bar {};
extern "C" void foo(struct Bar);

//--- A.cppm
module;
#include "foo.h"
export module A;
export extern "C" using ::foo;
//--- B.cppm
module;
import A;
export module B;

//--- C.cpp
// expected-no-diagnostics
import B;
#include "foo.h"
void test() {
  foo(Bar());
}

It seems the comment above the assert is correct, but the assert itself is missing the implicit global module case, which is also in module purview.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Matheus Izvekov (mizvekov)

Repro: ```C++ //--- A.cppm module; export module A; export extern "C" void foo(struct Bar);

//--- B.cppm
module;
import A;
export module B;

//--- C.cpp
import B;
struct Bar {};
void test() {
foo(Bar());
}

Crashes with:

Assertion failed: (FM && FM->isNamedModule() && !FM->isPrivateModule() && "bad export context"), function ArgumentDependentLookup, file SemaLookup.cpp, line 3854.

This is not just a crash on invalid. Slightly more complex, but valid, example:
```C++
//--- foo.h
struct Bar {};
extern "C" void foo(struct Bar);

//--- A.cppm
module;
#include "foo.h"
export module A;
export extern "C" using ::foo;
//--- B.cppm
module;
import A;
export module B;

//--- C.cpp
// expected-no-diagnostics
import B;
#include "foo.h"
void test() {
  foo(Bar());
}

It seems the comment above the assert is correct, but the assert itself is missing the implicit global module case, which is also in module purview.

[shafik]

CC @ChuanqiXu9