posix_spawn: handle executable being a directory

process.c

@@ -4759,7 +4759,16 @@ rb_posix_spawn(struct rb_execarg *eargp)
  // posix_spawn only returns fork/vfork/clone failures.
  // If it failed but errno == 0, then it must be an "exec" failure.
  if (errno == 0) {
- eaccess(abspath, X_OK);
+ if (!eaccess(abspath, X_OK)) {
+ // abspath is executable
+ struct stat file_stat;
+ if (stat(abspath, &file_stat)) {
+ rb_sys_fail(abspath);
+ }
+ if (S_ISDIR(file_stat.st_mode)) {
+ errno = EISDIR;
+ }
+ }
  }
  rb_sys_fail(abspath);
  }