<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/135158>135158</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc][test] `libc/test/UnitTest/FEnvSafeTest.cpp` is not hermetic
        </td>
    </tr>

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

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

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

<pre>
    The test in `FEnvSafeTest.cpp` is not hermetic and causes build errors on Nix when using clang with no stdlib headers.

```txt
libc> FAILED: libc/test/UnitTest/CMakeFiles/LibcFPTestHelpers.unit.dir/FEnvSafeTest.cpp.o
libc> /nix/store/zpx4f2s63nqkc14jlc08n6xgj3vr2y6l-clang-wrapper-21.0.0-unstable-2025-04-09/bin/clang++ -DLIBC_NAMESPACE=__llvm_libc_21_0_0_git -DTARGET_SUPPORTS_CLOCK -I/build/libc-src-21.0.0-unstable-2025-04-09/libc -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wno-comment -Wstring-conversion -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=gnu++17 -fpie -ffixed-point -Wconversion -Wno-sign-conversion -Wimplicit-fallthrough -Wwrite-strings -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wstrict-prototypes -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wthread-safety -MD -MT libc/test/UnitTest/CMakeFiles/LibcFPTestHelpers.unit.dir/FEnvSafeTest.cpp.o -MF libc/test/UnitTest/CMakeFiles/LibcFPTestHelpers.unit.dir/FEnvSafeTest.cpp.o.d -o libc/test/UnitTest/CMakeFiles/LibcFPTestHelpers.unit.dir/FEnvSafeTest.cpp.o -c /build/libc-src-21.0.0-unstable-2025-04-09/libc/test/UnitTest/FEnvSafeTest.cpp
libc> In file included from /build/libc-src-21.0.0-unstable-2025-04-09/libc/test/UnitTest/FEnvSafeTest.cpp:9:
libc> In file included from /build/libc-src-21.0.0-unstable-2025-04-09/libc/test/UnitTest/FEnvSafeTest.h:12:
libc> In file included from /build/libc-src-21.0.0-unstable-2025-04-09/libc/hdr/types/fenv_t.h:18:
libc> In file included from /nix/store/4kgdnwbxq9h8qm5ckrq2hdl59gzhjh62-gcc-14-20241116/include/c++/14-20241116/fenv.h:34:
libc> In file included from /nix/store/4kgdnwbxq9h8qm5ckrq2hdl59gzhjh62-gcc-14-20241116/include/c++/14-20241116/aarch64-unknown-linux-gnu/bits/c++config.h:680:
libc> /nix/store/4kgdnwbxq9h8qm5ckrq2hdl59gzhjh62-gcc-14-20241116/include/c++/14-20241116/aarch64-unknown-linux-gnu/bits/os_defines.h:39:10: fatal error: 'features.h' file not found
libc>    39 | #include <features.h>
libc>       |          ^~~~~~~~~~~~
libc> 1 error generated.
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzMVlFv27gP_zTKi6DAlu00echD2sT7F_92K9YOfQxkibbZypIryUm6h_vsBzndNd12h-GA4mYYcCL9SP5IihSF99gYgCUpzkmxnoghtNYtq7huB4OHSWXV8_KuBRrAB4qGkllSbszuVtRwBz5MZd-TWULRU2MDbcF1EFBSYRSVYvDgaTWgVhScs85Ta-hHPNB9C4YOHk1DpRamoXsMLTWW-qA0VrQFocD5KUlW8Z0lxzccAklWGitJsg0tV5dXmzXJVnRc4WXkSHj5xWC4O_68uBaPUKIGT3h5hZUsb-LO_0D3Uf1gMEwVOsLL752a2hNLhJcGD4SXPlgHhJdf-0Necz_LzNOjTPMHLZO5mR2ah2zn-PNMs9Ertnei78Exnk6TacIG44OoNDCe8IIlOUsWhJcVGsLLUYDwc8LPKVtfXZ5fbD-urje3N6uLDcnW263Wu24bCW15uk22ybbBQNn6bvX5w-Zue_vl5ubT57vb7cXVp4v_U3YZFcfAE15GIead_GcaEUXZ_Zgnkq2VCMACdnCyNphmEE6BYmInUIsKNYZnZmBP2b3QOkIPwQnK7o1lgxk8KNYLJzoI4Ci73zsMwHxwaBpP2b0UPrCnQUTJDn08D6xG0IqhwYBC41dwEYhdr1FiYLXQOrTODk0b5e0OHCjm9xhkyxTUYtDhaN5YOEjoAwvPPYxLhu3QhUFopoKNdBRoCMB-smMsk7brwERlR75MWrMD59EaymqFojHWB5SeSaujUF0PRga0hnkYvz7iRBAn_z9llK0_rjfnXz5Q5oMi2boxwzHt6RlldY8QNeEhRs7iaP_UcGQWa_YNm78Lz_fhjl4tFgwOAYw_EoprjRkYdqJBI9xzVOyDMC9R7EEJEwv6GAYZWO9ssDGm_lu6mYcOIxz2Gg0wsPUx3r11x4Pmn32AjqGRelDAehEivdA6EIp5UUN4pux6Tdn13fvUMmXX5ftonirK7HuRlvRflfFPmfzQtV_b26WhNWqgL_lRtHa2e0_T2WpBstV_xaAl2Srl70mgVTGjY5EQXtZgdtsXs_NfNPv2uskfG2X21eFp0c6fukI-uifeKl0smq_tQzvjrJGSpXnkkqdpOiO8fNEYb5ZjeyG8fIuItEZSWf77kBLCyXaWs8E8Grs3TKMZDmzskWWFwb-KSmtqbEYHZvPkrQe_DVfrtwpqNOCPkY7HPo1kaS2C0PTlZl1Rws9qEGFwI5KfHTMQR6raDkad-EYpzRaUnF1QwrMXkpRkFyfi2eYtntIR_9dDis0fr88JNj0Sog0YcCKAmp5OXxO1zNQiW4gJLNOzPOdzns2LSbusZ0LKPJ_LdJEt0rxaFELWlayKebKY15BMcBmrJMnTJE2KLCmmsp7PC8nTLE_qxZlISJ5AJ1BP45Qzta6ZoPcDLNOsSIv5RIsKtB-nVM6PNcbjvOqWEc-qofEkTzT64F81BAx6nGxHgWJNivOxMRTrOMT-erP6cbqdDE4v2xB6H48dLwkvGwztUE2l7WIX0Ltvn3hdPoCMikeP4qF4cWq35H8GAAD__5IEvqI">