`#include <iostream>` makes it impossible to use `pipe` as a variable name

[hewillk]

#include <iostream>

int pipe;

https://godbolt.org/z/fqPhTzq1E
The latest libc++ rejects the above code with:

<source>:3:5: error: redefinition of 'pipe' as different kind of symbol
    3 | int pipe;
      |     ^
/usr/include/unistd.h:437:12: note: previous definition is here
  437 | extern int pipe (int __pipedes[2]) __THROW __wur;
      |            ^
1 error generated.

Note that Clang-17's libc++, libc++, and MSVC-STL accept it.

[mordante]

Mainly curious where did you spot this?
The issue is due to including unistd.h which is needed for isatty. I'm surprised it's not an issue for libstdc++, I'm sure they use isatty too (https://cplusplus.github.io/LWG/issue4044).

[frederick-vs-ja]

Mainly curious where did you spot this? The issue is due to including unistd.h which is needed for isatty. I'm surprised it's not an issue for libstdc++, I'm sure they use isatty too (https://cplusplus.github.io/LWG/issue4044).

libstdc++ only includes <unistd.h> in a separately compiled source file in order to avoid name conflict.
https://github.com/gcc-mirror/gcc/blob/f22a7ae8a96f7e5e330b12bd5045424619aa4926/libstdc%2B%2B-v3/src/c%2B%2B23/print.cc

[hewillk]

Mainly curious where did you spot this?

I had a small piece of code that defined a namespace named pipe, and then suddenly found that it could not be compiled in clang-trunk.

[mordante]

Thanks for the info. I'm testing a patch now once approved I'll request to cherry-pick it to the LLVM-18 release branch.