isatty on native Windows

[Bruno Haible]

On mingw, I'm seeing this test failure:

  test-ptsname_r.c:117: assertion failed
  FAIL: test-ptsname_r.exe

The reason is that our ptsname_r implementation assumes that isatty()
sets errno when it returns 0, but our isatty() replacement does not do this.
This fixes it (at least for mingw):


2012-02-04  Bruno Haible  <br...@clisp.org>

        isatty: Fix test failure of ptsname_r on native Windows.
        * lib/isatty.c (_isatty_nothrow): Upon exception, return 0, not -1,
        and don't set errno.
        (isatty): Test first whether fd is valid. Set errno when returning 0.

--- lib/isatty.c.orig   Sat Feb  4 19:11:06 2012
+++ lib/isatty.c        Sat Feb  4 19:00:50 2012
@@ -48,8 +48,7 @@
     }
   CATCH_MSVC_INVAL
     {
-      result = -1;
-      errno = EBADF;
+      result = 0;
     }
   DONE_MSVC_INVAL;
 
@@ -59,15 +58,24 @@
 # define _isatty_nothrow _isatty
 #endif
 
+/* Determine whether FD refers to a console device.  Return 1 if yes.
+   Return 0 and set errno if no. (ptsname_r relies on the errno value.)  */
 int
 isatty (int fd)
 {
-  /* _isatty (fd) tests whether GetFileType of the handle is FILE_TYPE_CHAR.  
*/
+  HANDLE h = (HANDLE) _get_osfhandle (fd);
+  if (h == INVALID_HANDLE_VALUE)
+    {
+      errno = EBADF;
+      return 0;
+    }
+  /* _isatty (fd) tests whether GetFileType of the handle is FILE_TYPE_CHAR.
+     But it does not set errno when it returns 0.  */
   if (_isatty_nothrow (fd))
     {
-      HANDLE h = (HANDLE) _get_osfhandle (fd);
-      return IsConsoleHandle (h);
+      if (IsConsoleHandle (h))
+        return 1;
     }
-  else
-    return 0;
+  errno = ENOTTY;
+  return 0;
 }