[PATCH 3/3] io: Sync fts with gnulib

[Adhemerval Zanella]

With both f5ee21eacc5be459a7d08b344196f2245a5de801 and
9ab4bbed73172085c57b38a337d3dc279b1043b0 to document better FTS_NOSTAT.

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 io/fts-common.c |  1 +
 io/fts.h        | 13 +++++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/io/fts-common.c b/io/fts-common.c
index 3825f0aeb4..8252d716f8 100644
--- a/io/fts-common.c
+++ b/io/fts-common.c
@@ -554,6 +554,7 @@ FTS_OPEN (char * const *argv,
                    FTS_XDEV) requires that.  */
                 if (defer_stat && root != NULL) {
                         p->fts_info = FTS_NSOK;
+                        p->fts_statp->st_mode = 0;
                         fts_set_stat_required(p, true);
                 } else {
                         p->fts_info = fts_stat(sp, p, false);
diff --git a/io/fts.h b/io/fts.h
index 50636e6c87..23518cba32 100644
--- a/io/fts.h
+++ b/io/fts.h
@@ -90,6 +90,13 @@ typedef struct {
 #define	FTS_COMFOLLOW	0x0001		/* follow command line symlinks */
 #define	FTS_LOGICAL	0x0002		/* logical walk */
 #define	FTS_NOCHDIR	0x0004		/* don't change directories */
+
+  /* For efficiency do not set *fts_statp except for fts_statp->st_mode,
+     which is set to zero if the file type is unknown,
+     and which otherwise has at least its S_IFMT type bits set.
+     When fts_info == FTS_NSOK this supports expressions like
+     (fts_statp->st_mode ? !!S_ISDIR (fts_statp->st_mode): -1), which yields
+     1 for a directory, 0 for a non-directory, and -1 for unknown.  */
 #define	FTS_NOSTAT	0x0008		/* don't get stat info */
 #define	FTS_PHYSICAL	0x0010		/* physical walk */
 #define	FTS_SEEDOT	0x0020		/* return dot and dot-dot */
@@ -139,10 +146,8 @@ typedef struct {
      Use this flag to make fts_open and fts_read defer the stat/lstat/fststat
      of each entry until it is actually processed.  However, note that if you
      use this option and also specify a comparison function, that function may
-     not examine any data via fts_statp.  However, when fts_statp->st_mode is
-     nonzero, the S_IFMT type bits are valid, with mapped dirent.d_type data.
-     Of course, that happens only on file systems that provide useful
-     dirent.d_type data.  */
+     not examine any data via fts_statp, other than fts_statp->st_mode
+     which is set similarly to how FTS_NOSTAT behaves.  */
 #define FTS_DEFER_STAT	0x1000
 
   /* Use this flag to disable stripping of trailing slashes
-- 
2.43.0