<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/151127>151127</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [regression, libcxx, C++26] __cpp_lib_filesystem is not available in libc++ until <fstream> is included
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++
      </td>
    </tr>

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

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

<pre>
    Consider the following code:

``` c++
#ifdef __cpp_lib_filesystem
#include <filesystem>
#endif

#include <fstream>

int main() {
#ifdef __cpp_lib_filesystem
  auto path = std::filesystem::current_path().string();
#endif
  return 0;
}
```

Compiling in C++23 mode works both with Clang 19 and 20 (version details below):

```
clang++ -std=c++23 -stdlib=libc++ fs.cpp
```

Compiling in C++26 mode fails with the following error:

```
$ clang++ -std=c++26 -stdlib=libc++ fs.cpp
fs.cpp:9:30: error: no member named 'current_path' in namespace 'std::filesystem'
    9 | auto path = std::filesystem::current_path().string();
      | ~~~~~~~~~~~~~~~~~^
1 error generated.
```

only when using Clang 20 on Arch Linux:

```
$ clang++ --version
clang version 20.1.8
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
```

but compiles fine when using Clang 19 on FreeBSD:

```
% clang++ --version
FreeBSD clang version 19.1.7 (https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2)
Target: x86_64-unknown-freebsd14.3
Thread model: posix
InstalledDir: /usr/bin
```
</pre>
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