os_nodetype: rework

Make the Windows impl closer to Vim os_win32.c, and the Unix impl closer
to Vim os_unix.c.

Outcomes:
- Do not send negative fd to close(). ref #4806 #4772 #6860
- Fallback return-value is now correct in (hopefully) all cases.
- unix: check S_ISXXX instead of relying on os_open (which can fail for
  irrelevant reasons). buf_write() expects NODE_WRITABLE for character
  devices such as /dev/stderr. 96f834a842

src/nvim/os/fs.c

@@ -133,22 +133,12 @@ bool os_isdir(const char_u *name)
 int os_nodetype(const char *name)
   FUNC_ATTR_NONNULL_ALL
 {
-#ifdef WIN32
+#ifndef WIN32  // Unix
-  // Edge case from Vim os_win32.c:
-  // We can't open a file with a name "\\.\con" or "\\.\prn", trying to read
-  // from it later will cause Vim to hang. Thus return NODE_WRITABLE here.
-  if (STRNCMP(name, "\\\\.\\", 4) == 0) {
-    return NODE_WRITABLE;
-  }
-#endif
-
   uv_stat_t statbuf;
   if (0 != os_stat(name, &statbuf)) {
     return NODE_NORMAL;  // File doesn't exist.
   }
-
+  // uv_handle_type does not distinguish BLK and DIR.
-#ifndef WIN32
-  // libuv does not handle BLK and DIR in uv_handle_type.
   //    Related: https://github.com/joyent/libuv/pull/1421
   if (S_ISREG(statbuf.st_mode) || S_ISDIR(statbuf.st_mode)) {
     return NODE_NORMAL;
@@ -156,48 +146,51 @@ int os_nodetype(const char *name)
   if (S_ISBLK(statbuf.st_mode)) {  // block device isn't writable
     return NODE_OTHER;
   }
-#endif
+  // Everything else is writable?
+  // buf_write() expects NODE_WRITABLE for char device /dev/stderr.
+  return NODE_WRITABLE;
+#else  // Windows
+  // Edge case from Vim os_win32.c:
+  // We can't open a file with a name "\\.\con" or "\\.\prn", trying to read
+  // from it later will cause Vim to hang. Thus return NODE_WRITABLE here.
+  if (STRNCMP(name, "\\\\.\\", 4) == 0) {
+    return NODE_WRITABLE;
+  }
 
-  // Vim os_win32.c:mch_nodetype does this (since patch 7.4.015):
+  // Vim os_win32.c:mch_nodetype does (since 7.4.015):
-  //    if (enc_codepage >= 0 && (int)GetACP() != enc_codepage) {
   //    wn = enc_to_utf16(name, NULL);
   //    hFile = CreatFile(wn, ...)
-  // to get a HANDLE. But libuv just calls win32's _get_osfhandle() on the fd we
+  // to get a HANDLE. Whereas libuv just calls _get_osfhandle() on the fd we
-  // give it. uv_fs_open calls fs__capture_path which does a similar dance and
+  // give it. But uv_fs_open later calls fs__capture_path which does a similar
-  // saves us the hassle.
+  // utf8-to-utf16 dance and saves us the hassle.
 
-  int nodetype = NODE_WRITABLE;
+  // macOS: os_open(/dev/stderr) would return UV_EACCES.
   int fd = os_open(name, O_RDONLY
 # ifdef O_NONBLOCK
                    | O_NONBLOCK
 # endif
                    , 0);
-  if (fd == UV_EINVAL) {
+  if (fd < 0) {  // open() failed.
-    return NODE_OTHER;  // open() failed.
+    return NODE_NORMAL;
+  }
+  int guess = uv_guess_handle(fd);
+  if (close(fd) == -1) {
+    ELOG("close(%d) failed. name='%s'", fd, name);
   }
 
-  switch (uv_guess_handle(fd)) {
+  switch (guess) {
     case UV_TTY:          // FILE_TYPE_CHAR
-      nodetype = NODE_WRITABLE;
+      return NODE_WRITABLE;
-      break;
     case UV_FILE:         // FILE_TYPE_DISK
-      nodetype = NODE_NORMAL;
+      return NODE_NORMAL;
-      break;
     case UV_NAMED_PIPE:   // not handled explicitly in Vim os_win32.c
     case UV_UDP:          // unix only
     case UV_TCP:          // unix only
     case UV_UNKNOWN_HANDLE:
     default:
-#ifdef WIN32
+      return NODE_OTHER;  // Vim os_win32.c default
-      nodetype = NODE_NORMAL;
-#else
-      nodetype = NODE_WRITABLE;  // Everything else is writable?
-#endif
-      break;
   }
-
+#endif
-  close(fd);
-  return nodetype;
 }
 
 /// Gets the absolute path of the currently running executable.
@@ -1080,7 +1073,8 @@ shortcut_end:
 
 #endif
 
-int os_translate_sys_error(int sys_errno) {
+int os_translate_sys_error(int sys_errno)
+{
 #ifdef HAVE_UV_TRANSLATE_SYS_ERROR
   return uv_translate_sys_error(sys_errno);
 #elif defined(WIN32)