https://bugs.llvm.org/show_bug.cgi?id=52531
Bug ID: 52531
Summary: [C++20] [Module] The combination of iostream and file
with .cppm suffix would crash
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: C++2a
Assignee: unassignedclangbugs at nondot.org
Reporter: yedeng.yd at linux.alibaba.com
CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk
I met an interesting bug which would happen only if iosstream and module file
end with `.cppm`.
Here is the reproducer:
```C++
// Hello.cppm
module;
#include <iostream>
export module Hello;
export void SayHello()
{
std::cout << "Hello World.\n";
}
// main.cpp
import Hello;
int main() {
SayHello();
return 0;
}
```
And if I compile it as:
```
clang++ -std=c++20 --precompile Hello.cppm -o Hello.pcm
clang++ -std=c++20 -fprebuilt-module-path=. Hello.pcm main.cpp
```
And the generated executable would crash.
Interestingly, it wouldn't crash if we use `std::printf` instead of `std::cout`
```C++
// Hello.cppm
module;
#include <cstdio>
export module Hello;
export void SayHello()
{
std::printf("Hello World.\n");
}
// main.cpp
import Hello;
int main() {
SayHello();
return 0;
}
```
Also, it wouldn't crash if the suffix is `cpp` instead of `cppm`. For example:
```C++
// Hello.cpp
module;
#include <iostream>
export module Hello;
export void SayHello()
{
std::cout << "Hello World.\n";
}
// main.cpp
import Hello;
int main() {
SayHello();
return 0;
}
```
Compile argument:
```
clang++ -std=c++20 -Xclang -emit-module-interface Hello.cpp -o Hello.pcm
clang++ -std=c++20 -fprebuilt-module-path=. say_hello.cpp main.cpp
```
I am not sure if this is a bug in compiler or in runtime. It is appreciate if
someone could help to confirm this.
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