Avoid GNU getcwd extension behavior

[bbannier]

GNU getcwd can allocate a buffer if passed NULL for it. This is an extension which is e.g., not recognized by clang-tidy-19's StdCLibraryFunctions check¹ which emits a diagnostic on a violated precondition buf != NULL,

The 1st argument to 'getcwd' is NULL but should not be NULL [clang-analyzer-unix.StdCLibraryFunctions,-warnings-as-errors]
[build]  3987 |     std::unique_ptr<char, decltype(&std::free)> buffer{::getcwd(NULL, 0), std::free};

This patch modifies this use of getcwd with this extension behavior to instead use get_current_dir_name which is also a GNU extension, but does not trigger this diagnostic.

Footnotes

1. https://clang.llvm.org/docs/analyzer/checkers.html#unix-stdclibraryfunctions-c ↩

[bbannier]

I added a commit switching from centos CI over to rockylinux (latest two releases). Let me know whether you would like me to pull that into a separate PR.

[bbannier]

@gulrak, anything I could do to pique your interest in this patch? I am having trouble suppressing it in my clang-tidy setup, but would prefer keeping the check globally enabled.

An alternative approach would be to suppress the check for just this line (I see that there are already some suppression in this project), e.g., by prefixing it with

   // NOLINTNEXTLINE(clang-analyzer-unix.StdCLibraryFunctions)

[gulrak]

Sorry, for me not reacting quicker, but you are right, that is a better solution. I was, for a moment, thinking if one might switch to something along the lines (but slightly to be adapted) of the no extension needing suggested code snippet from the documentation, like

char *
gnu_getcwd ()
{
  size_t size = 100;

  while (1)
    {
      char *buffer = (char *) xmalloc (size);
      if (getcwd (buffer, size) == buffer)
        return buffer;
      free (buffer);
      if (errno != ERANGE)
        return 0;
      size *= 2;
    }
}

But on the base that it currently uses the extensions, I think your solution is a quick and easy one, and I'm all for not having exceptions in tidy.

I'm at work currently, but will merge it later today.

Thanks for the PR and the nagging. ;-)