cp: fix --link regarding the dereferencing of symbolic links

* src/copy.c (create_hard_link): Add a bool 'dereference' parameter,
and pass AT_SYMLINK_FOLLOW as 'flags' to linkat() when dereference
is true.
(should_dereference): Add new 'bool' function to determine if a
file should be dereferenced or not.
(copy_internal): Use the above new should_dereference() and remember
its return value in a new local bool 'dereference' variable.  Use that
in all three calls to create_hard_link().
* src/cp.c (main): after parsing the options, if x.dereference is
still DEFEF_UNDEFINED and the x.recursive is true, then only set
x.dereference to DEREF_NEVER iff --link was not specified.
* doc/coreutils.texi (cp invocation): Mention that cp(1) does not
follow symbolic links in the source when --link is specified.
Likewise in the description of the -R option when used together with
that option.
* tests/cp/same-file.sh: Adapt the expected results for the -fl,
the -bl and the -bfl tests.
* tests/cp/link-deref.sh: Add a new test.
* tests/local.mk (all_tests): Reference the above new test.
* NEWS (Changes in behavior): Mention the change.

This fixes http://bugs.gnu.org/15173

Co-authored-by: Bernhard Voelker <mail@bernhard-voelker.de>

3 files changed, 114 insertions, 3 deletions

diff --git a/tests/cp/link-deref.sh b/tests/cp/link-deref.sh
new file mode 100755
index 000000000..91a6c5de3
--- /dev/null
+++ b/tests/cp/link-deref.sh
@@ -0,0 +1,110 @@
+#!/bin/sh
+# Exercise cp --link's behavior regarding the dereferencing of symbolic links.
+
+# Copyright (C) 2013 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ cp
+
+mkdir dir              || framework_failure_
+: > file               || framework_failure_
+ln -s dir     dirlink  || framework_failure_
+ln -s file    filelink || framework_failure_
+ln -s nowhere danglink || framework_failure_
+
+# printf format of the output line.
+outformat='%s|result=%s|inode=%s|type=%s|error=%s\n'
+
+for src in dirlink filelink danglink; do
+  # Get symlink's target.
+  tgt=$(readlink $src) || framework_failure_
+  # Get inodes and file type of the symlink (src) and its target (tgt).
+  # Note: this will fail for 'danglink'; catch it.
+  ino_src="$(stat -c '%i' $src)" || framework_failure_
+  typ_src="$(stat -c '%F' $src)" || framework_failure_
+  ino_tgt="$(stat -c '%i' $tgt 2>/dev/null)" || ino_tgt=
+  typ_tgt="$(stat -c '%F' $tgt 2>/dev/null)" || typ_tgt=
+
+  for o in '' -L -H -P; do
+    for r in '' -R; do
+
+      command="cp --link $o $r $src dst"
+      $command 2> err
+      result=$?
+
+      # Get inode and file type of the destination (which may fail, too).
+      ino_dst="$(stat -c '%i' dst 2>/dev/null)" || ini_dst=
+      typ_dst="$(stat -c '%F' dst 2>/dev/null)" || typ_dst=
+
+      # Print the actual result in a certain format.
+      printf "$outformat" \
+        "$command"   \
+        "$result"   \
+        "$ino_dst"  \
+        "$typ_dst"  \
+        "$(< err)"  \
+        > out
+
+      # What was expected?
+      if [ "$o" = "-P" ]; then
+        # cp --link should not dereference if -P is given.
+        exp_result=0
+        exp_inode=$ino_src
+        exp_ftype=$typ_src
+        exp_error=
+      elif [ "$src" = 'danglink' ]; then
+        # Dereferencing should fail for the 'danglink'.
+        exp_result=1
+        exp_inode=
+        exp_ftype=
+        exp_error="cp: cannot stat 'danglink': No such file or directory"
+      elif [ "$src" = 'dirlink' ] && [ "$r" != '-R' ]; then
+        # Dereferencing should fail for the 'dirlink' without -R.
+        exp_result=1
+        exp_inode=
+        exp_ftype=
+        exp_error="cp: omitting directory 'dirlink'"
+      elif [ "$src" = 'dirlink' ]; then
+        # cp --link -R 'dirlink' should create a new directory.
+        exp_result=0
+        exp_inode=$ino_dst
+        exp_ftype=$typ_dst
+        exp_error=
+      else
+        # cp --link 'filelink' should create a hard link to the target.
+        exp_result=0
+        exp_inode=$ino_tgt
+        exp_ftype=$typ_tgt
+        exp_error=
+      fi
+
+      # Print the expected result in a certain format.
+      printf "$outformat" \
+        "$command"   \
+        "$exp_result" \
+        "$exp_inode"  \
+        "$exp_ftype"  \
+        "$exp_error"  \
+        > exp
+
+      compare exp out || { ls -lid $src $tgt dst; fail=1; }
+
+      rm -rf dst err exp out || framework_failure_
+    done
+  done
+done
+
+Exit $fail
diff --git a/tests/cp/same-file.sh b/tests/cp/same-file.sh
index 003a62ba7..326f9c6bd 100755
--- a/tests/cp/same-file.sh
+++ b/tests/cp/same-file.sh
@@ -189,9 +189,9 @@ cat <<\EOF | sed "$remove_these_sed" > expected
 0 -bf (foo sl1 -> foo sl2 sl2.~1~ -> foo)
 0 -bdf (foo sl1 -> foo sl2 -> foo sl2.~1~ -> foo)
 1 -l [cp: cannot create hard link 'sl2' to 'sl1'] (foo sl1 -> foo sl2 -> foo)
-0 -fl (foo sl1 -> foo sl2 -> foo)
-0 -bl (foo sl1 -> foo sl2 -> foo sl2.~1~ -> foo)
-0 -bfl (foo sl1 -> foo sl2 -> foo sl2.~1~ -> foo)
+0 -fl (foo sl1 -> foo sl2)
+0 -bl (foo sl1 -> foo sl2 sl2.~1~ -> foo)
+0 -bfl (foo sl1 -> foo sl2 sl2.~1~ -> foo)
 
 1 [cp: 'foo' and 'hardlink' are the same file] (foo hardlink)
 1 -d [cp: 'foo' and 'hardlink' are the same file] (foo hardlink)
diff --git a/tests/local.mk b/tests/local.mk
index e18deacc7..3c924255f 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -427,6 +427,7 @@ all_tests =					\
   tests/cp/file-perm-race.sh			\
   tests/cp/into-self.sh				\
   tests/cp/link.sh				\
+  tests/cp/link-deref.sh			\
   tests/cp/link-no-deref.sh			\
   tests/cp/link-preserve.sh			\
   tests/cp/link-symlink.sh			\