<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/164074>164074</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libcxx][CMake] `LIBCXX_ENABLE_FILESYSTEM=OFF` is not respected on Windows for freestanding runtimes build
        </td>
    </tr>

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

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

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

<pre>
    When configuring a freestanding libcxx build on Windows using the runtimes build entrypoint, setting `-DLIBCXX_ENABLE_FILESYSTEM=OFF` does not prevent filesystem source files from being added to the build target. This results in a compilation failure, as these sources have dependencies (e.g, Unicode, wide characters)  that are typically disabled in such a configuration.

This issue does not occur on Linux with an identical configruation.

## Environment
* OS: Windows 10 22H2
* Compiler: Clang 21.1.1 (From MSYS2 `clang64` toolchain)
* Build System: Ninja
* LLVM commit: `main` branch

## Reproduction

1. From the root of `llvm-project`, run the following CMake command:
```bash
cmake -G Ninja -S runtimes -B build-freestanding 
-DLLVM_ENABLE_RUNTIMES=libcxx
-DCMAKE_BUILD_TYPE=Release
-DCMAKE_INSTALL_PREFIX=install
-DCMAKE_C_COMPILER=clang
-DCMAKE_CXX_COMPILER=clang++
-DLIBCXX_ENABLE_SHARED=OFF
-DLIBCXX_ENABLE_STATIC=ON
-DLIBCXX_CXX_ABI=none
-DLIBCXX_ENABLE_EXCEPTIONS=OFF
-DLIBCXX_ENABLE_RTTI=OFF
-DLIBCXX_ENABLE_FILESYSTEM=OFF
-DLIBCXX_ENABLE_LOCALIZATION=OFF
-DLIBCXX_ENABLE_UNICODE=OFF
-DLIBCXX_ENABLE_WIDE_CHARACTERS=OFF
-DLIBCXX_ENABLE_THREADS=OFF
-DLIBCXX_ENABLE_MONOTONIC_CLOCK=OFF
-DLIBCXX_ENABLE_TIME_ZONE_DATABASE=OFF
-DLIBCXX_ENABLE_RANDOM_DEVICE=OFF
-DLIBCXX_ENABLE_NEW_DELETE_DEFINITIONS=OFF
-DLIBCXX_INCLUDE_TESTS=OFF
-DLIBCXX_INCLUDE_BENCHMARKS=OFF
-DLIBCXX_USE_COMPILER_RT=ON
```

2. Go to the build directoryt and run `ninja`:
```
cd build-freestanding
ninja
```

## Actual Behavior

The build fails with compilation errors in filesystem-related source files.
```
... llvm-project/build-freestanding/include/c++/v1/__filesystem/path.h:186:9: error: unknown type name 'wstring'; did you mean 'string'?
  186 | typedef wstring __path_string;
      |         ^~~~~~~
      |         string
... llvm-project/build-freestanding/include/c++/v1/__fwd/string.h:45:7: note: 'string' declared here
   45 | using string = basic_string<char>;
      | ^
```

## Expected Behavior

The build should succeed. Source files from the `libcxx/src/filesystem`  directory should not be part of the build when `LIBCXX_ENABLE_FILESYSTEM` is `OFF`.

## Speculation

Probable root cause is in `libcxx/src/CMakeLists.txt`. Filesystem source files (`filesystem_*.cpp`) are unconditionally added to the `LIBCXX_SOURCES` variable.

These files should be moved inside the guard for `LIBCXX_ENABLE_FILESYSTEM` block.
</pre>
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