[PATCH] cp: Add --keep-directory-symlink option

[Daan De Meyer]

When recursively copying files into OS trees, it often happens that
some subdirectory of the source directory is a symlink in the target
directory. Currently, cp will fail in that scenario with the error:

"cannot overwrite non-directory %s with directory %s"

However, we'd like cp in this scenario to follow the destination
directory symlink and copy the files into the symlinked directory
instead. Let's support this by adding a new option
--keep-directory-symlink that makes cp follow destination directory
symlinks.

We name the option --keep-directory-symlink to keep consistent with
tar which has the same option with the same effect.
---
 doc/coreutils.texi                 |  4 ++++
 src/copy.c                         |  3 ++-
 src/copy.h                         |  3 +++
 src/cp.c                           | 12 +++++++++++-
 tests/cp/keep-directory-symlink.sh | 27 +++++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100755 tests/cp/keep-directory-symlink.sh

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index d445ea228..51c460929 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -10281,6 +10281,10 @@ option is also specified.
 @opindex --verbose
 Print the name of each file before moving it.
 
+@item --keep-directory-symlink
+@opindex --keep-directory-symlink
+Follow existing symlinks to directories when copying.
+
 @optStripTrailingSlashes
 
 @optBackupSuffix
diff --git a/src/copy.c b/src/copy.c
index f54253e5b..bbadca293 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -2311,7 +2311,8 @@ copy_internal (char const *src_name, char const *dst_name,
           bool use_lstat
             = ((! S_ISREG (src_mode)
                 && (! x->copy_as_regular
-                    || S_ISDIR (src_mode) || S_ISLNK (src_mode)))
+                    || (S_ISDIR (src_mode) && !x->keep_directory_symlink)
+                    || S_ISLNK (src_mode)))
                || x->move_mode || x->symbolic_link || x->hard_link
                || x->backup_type != no_backups
                || x->unlink_dest_before_opening);
diff --git a/src/copy.h b/src/copy.h
index 3809f8d23..834685c51 100644
--- a/src/copy.h
+++ b/src/copy.h
@@ -256,6 +256,9 @@ struct cp_options
   /* If true, display the names of the files before copying them. */
   bool verbose;
 
+  /* If true, follow existing symlinks to directories when copying. */
+  bool keep_directory_symlink;
+
   /* If true, display details of how files were copied.  */
   bool debug;
 
diff --git a/src/cp.c b/src/cp.c
index 04a5cbee3..992d28e1e 100644
--- a/src/cp.c
+++ b/src/cp.c
@@ -68,7 +68,8 @@ enum
   REFLINK_OPTION,
   SPARSE_OPTION,
   STRIP_TRAILING_SLASHES_OPTION,
-  UNLINK_DEST_BEFORE_OPENING
+  UNLINK_DEST_BEFORE_OPENING,
+  KEEP_DIRECTORY_SYMLINK_OPTION
 };
 
 /* True if the kernel is SELinux enabled.  */
@@ -141,6 +142,7 @@ static struct option const long_opts[] =
   {"target-directory", required_argument, nullptr, 't'},
   {"update", optional_argument, nullptr, 'u'},
   {"verbose", no_argument, nullptr, 'v'},
+  {"keep-directory-symlink", no_argument, nullptr, 
KEEP_DIRECTORY_SYMLINK_OPTION},
   {GETOPT_SELINUX_CONTEXT_OPTION_DECL},
   {GETOPT_HELP_OPTION_DECL},
   {GETOPT_VERSION_OPTION_DECL},
@@ -230,6 +232,9 @@ Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.\n\
 "), stdout);
       fputs (_("\
   -v, --verbose                explain what is being done\n\
+"), stdout);
+      fputs (_("\
+      --keep-directory-symlink  preserve existing symlinks to directories\n\
 "), stdout);
       fputs (_("\
   -x, --one-file-system        stay on this file system\n\
@@ -859,6 +864,7 @@ cp_option_init (struct cp_options *x)
 
   x->update = false;
   x->verbose = false;
+  x->keep_directory_symlink = false;
 
   /* By default, refuse to open a dangling destination symlink, because
      in general one cannot do that safely, give the current semantics of
@@ -1161,6 +1167,10 @@ main (int argc, char **argv)
           x.verbose = true;
           break;
 
+        case KEEP_DIRECTORY_SYMLINK_OPTION:
+          x.keep_directory_symlink = true;
+          break;
+
         case 'x':
           x.one_file_system = true;
           break;
diff --git a/tests/cp/keep-directory-symlink.sh 
b/tests/cp/keep-directory-symlink.sh
new file mode 100755
index 000000000..6ae116cd8
--- /dev/null
+++ b/tests/cp/keep-directory-symlink.sh
@@ -0,0 +1,27 @@
+#!/bin/sh
+# Test that cp --keep-directory-symlink follows symlinks.
+
+# Copyright (C) 2006-2023 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 <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ cp
+
+mkdir -p a/b b/d/e || framework_failure_
+ln -s b a/d || framework_failure_
+
+cp -RT --copy-contents b a && framework_failure_
+cp -RT --copy-contents --keep-directory-symlink b a || framework_failure_
+ls a/b/e
-- 
2.43.0