Avoid most stat calls when completing file names

* admin/merge-gnulib (GNULIB_MODULES): Add d-type.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* m4/d-type.m4: New file, copied from gnulib.
* src/dired.c (DT_UNKNOWN, DT_DIR, DT_LINK)
[!HAVE_STRUCT_DIRENT_D_TYPE]: New constants.
(dirent_type): New function.
(file_name_completion): Use it, to avoid unnecessary calls to
stat-like functions on GNU/Linux and other platforms with d_type.
(file_name_completion_stat): Just follow the link; there is no
need to try first with AT_SYMLINK_NOFOLLOW since the directory
entry was already checked to exist.

2 files changed, 35 insertions, 0 deletions

diff --git a/m4/d-type.m4 b/m4/d-type.m4
new file mode 100644
index 00000000000..c819fc02f84
--- /dev/null
+++ b/m4/d-type.m4
@@ -0,0 +1,32 @@
+# serial 12
+
+dnl From Jim Meyering.
+dnl
+dnl Check whether struct dirent has a member named d_type.
+dnl
+
+# Copyright (C) 1997, 1999-2004, 2006, 2009-2017 Free Software Foundation, Inc.
+#
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_CHECK_TYPE_STRUCT_DIRENT_D_TYPE],
+  [AC_CACHE_CHECK([for d_type member in directory struct],
+                  [gl_cv_struct_dirent_d_type],
+     [AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#include <sys/types.h>
+#include <dirent.h>
+         ]],
+         [[struct dirent dp; dp.d_type = 0;]])],
+       [gl_cv_struct_dirent_d_type=yes],
+       [gl_cv_struct_dirent_d_type=no])
+     ]
+   )
+   if test $gl_cv_struct_dirent_d_type = yes; then
+     AC_DEFINE([HAVE_STRUCT_DIRENT_D_TYPE], [1],
+       [Define if there is a member named d_type in the struct describing
+        directory headers.])
+   fi
+  ]
+)
diff --git a/m4/gnulib-comp.m4 b/m4/gnulib-comp.m4
index 2f135773930..188c116c851 100644
--- a/m4/gnulib-comp.m4
+++ b/m4/gnulib-comp.m4
@@ -61,6 +61,7 @@ AC_DEFUN([gl_EARLY],
   # Code from module crypto/sha1:
   # Code from module crypto/sha256:
   # Code from module crypto/sha512:
+  # Code from module d-type:
   # Code from module diffseq:
   # Code from module dirent:
   # Code from module dirfd:
@@ -199,6 +200,7 @@ AC_DEFUN([gl_INIT],
   gl_SHA1
   gl_SHA256
   gl_SHA512
+  gl_CHECK_TYPE_STRUCT_DIRENT_D_TYPE
   gl_DIRENT_H
   AC_REQUIRE([gl_C99_STRTOLD])
   gl_FUNC_DUP2
@@ -968,6 +970,7 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/count-leading-zeros.m4
   m4/count-one-bits.m4
   m4/count-trailing-zeros.m4
+  m4/d-type.m4
   m4/dirent_h.m4
   m4/dirfd.m4
   m4/dup2.m4