Improve rename-file behavior on macOS

Problem reported by Philipp Stephani (Bug#27986).
* src/fileio.c (Frename_file):
Worry about file name case sensitivity only if CYGWIN or DOS_NT.
* src/sysdep.c (renameat_noreplace): Use renameatx_np on macOS,
since this provides the necessary atomicity guarantees.

2 files changed, 6 insertions, 2 deletions

diff --git a/src/fileio.c b/src/fileio.c
index 69079c6ae49..9f6de5b6ca7 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2259,12 +2259,14 @@ This is what happens in interactive use with M-x.  */)
      not worry whether NEWNAME exists or whether it is a directory, as
      it is already another name for FILE.  */
   bool case_only_rename = false;
+#if defined CYGWIN || defined DOS_NT
   if (!NILP (Ffile_name_case_insensitive_p (file)))
     {
       newname = Fexpand_file_name (newname, Qnil);
       case_only_rename = !NILP (Fstring_equal (Fdowncase (file),
                                                Fdowncase (newname)));
     }
+#endif
 
   if (!case_only_rename)
     newname = expand_cp_target (Fdirectory_file_name (file), newname);
diff --git a/src/sysdep.c b/src/sysdep.c
index 35f499c1853..2e18a419e3f 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -2693,11 +2693,13 @@ renameat_noreplace (int srcfd, char const *src, int dstfd, char const *dst)
 {
 #if defined SYS_renameat2 && defined RENAME_NOREPLACE
   return syscall (SYS_renameat2, srcfd, src, dstfd, dst, RENAME_NOREPLACE);
+#elif defined RENAME_EXCL
+  return renameatx_np (srcfd, src, dstfd, dst, RENAME_EXCL);
 #else
-#ifdef WINDOWSNT
+# ifdef WINDOWSNT
   if (srcfd == AT_FDCWD && dstfd == AT_FDCWD)
     return sys_rename_replace (src, dst, 0);
-#endif
+# endif
   errno = ENOSYS;
   return -1;
 #endif