<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/99344>99344</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            "requires expression" contained in exported symbol name
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Ecordonnier
      </td>
    </tr>
</table>

<pre>
    [clang-test.zip](https://github.com/user-attachments/files/16268452/clang-test.zip)

See the test code that I attached. It compiles fine with clang++17, but fails with clang++18.
test.cpp defines a template specialization, and main.cpp calls this function:
test.cpp:
```
template<class T>
 requires(!std::is_same_v<T, std::string>)
std::optional<T> myFunction(std::string arg) {
    return std::optional<T>{};
}

template std::optional<int> myFunction<int>(std::string arg);
```
main.cpp:
```
int main()
{
    std::optional<int> foobar = myFunction<int>("foobar");
}
```

This gets compiled correctly with clang++17:
```
0000000000000000 W std::optional<int> myFunction<int>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)
```
 however with clang++18 the symbol name also contains the requires expression after the correct name of the function:
 ```
 0000000000000000 W std::optional<int> myFunction<int>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) requires !(std::is_same_v<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >)
 ```
 For that reason, the linker fails to find the symbol.

```
$ ./test.sh 
+ clang++-17 --version
Ubuntu clang version 17.0.6 (9ubuntu1)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
+ clang++-17 -std=c++20 -c test.cpp -o test-clang-17.o
+ clang++-17 -std=c++20 -c main.cpp -o main-clang.o
+ clang++-17 main-clang.o test-clang-17.o -o main-clang-17
+ nm --demangle test-clang-17.o
+ grep -i myFunc
0000000000000000 W std::optional<int> myFunction<int>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)

+ clang++-19 --version
Ubuntu clang version 19.0.0 (++20240516083551+51403ada789e-1~exp1~20240516083654.504)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-19/bin
+ clang++-19 -std=c++20 -c test.cpp -o test-clang-19.o
+ clang++-19 -std=c++20 -c main.cpp -o main-clang.o
+ clang++-19 main-clang.o test-clang-19.o -o main-clang-19
/usr/bin/ld: main-clang.o: in function `main':
main.cpp:(.text+0x2f): undefined reference to `std::optional<int> myFunction<int>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
clang++-19: error: linker command failed with exit code 1 (use -v to see invocation)
+ + nm --demangle test-clang-19.o
grep -i myFunc
0000000000000000 W std::optional<int> myFunction<int>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) requires !(std::is_same_v<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >)
```
</pre>
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