ln: fix replacing symbolic links whose targets can't exist

* src/ln.c (errno_nonexisting): A new function to determine if
the errno implies that a file doesn't or can't (currently) exist.
(target_directory_operand): Use the new function to expand the
set of errors we handle.
* tests/ln/sf-1.sh: Add test cases for the newly handled errors.
* THANKS.in: Mention the reporter.
* NEWS: Mention the bug fix.

4 files changed, 33 insertions, 3 deletions

diff --git a/NEWS b/NEWS
index 699a7d3a1..88a41547e 100644
--- a/NEWS
+++ b/NEWS
@@ -14,6 +14,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   when reading the SELinux context for a file.
   [bug introduced in coreutils-8.22]
 
+  ln -sf now replaces symbolic links whose targets can't exist.  Previously
+  it would display an error, requiring --no-dereference to avoid the issue.
+  [bug introduced in coreutils-5.3.0]
+
 
 * Noteworthy changes in release 8.22 (2013-12-13) [stable]
 
diff --git a/THANKS.in b/THANKS.in
index 5b3e96ed2..fb7d6e084 100644
--- a/THANKS.in
+++ b/THANKS.in
@@ -341,6 +341,7 @@ Kaveh R. Ghazi                      ghazi@caip.rutgers.edu
 Keith M. Briggs                     keith.briggs@bt.com
 Keith Owens                         kaos@audio.apana.org.au
 Keith Thompson                      kst@cts.com
+Ken Irving                          ken.irving@alaska.edu
 Ken Pizzini                         kenp@halcyon.com
 Kevin Mudrick                       kmudrick@healthmarketscience.com
 Kirk Kelsey                         kirk.kelsey@0x4b.net
diff --git a/src/ln.c b/src/ln.c
index b4903620b..aab9cf2fa 100644
--- a/src/ln.c
+++ b/src/ln.c
@@ -103,8 +103,18 @@ static struct option const long_options[] =
   {NULL, 0, NULL, 0}
 };
 
+/* Return true when the passed ERR implies
+   that a file does not or could not exist.  */
+
+static bool
+errno_nonexisting (int err)
+{
+  return err == ENOENT || err == ENAMETOOLONG || err == ENOTDIR || err == ELOOP;
+}
+
+
 /* FILE is the last operand of this command.  Return true if FILE is a
-   directory.  But report an error there is a problem accessing FILE,
+   directory.  But report an error if there is a problem accessing FILE,
    or if FILE does not exist but would have to refer to an existing
    directory if it referred to anything at all.  */
 
@@ -119,7 +129,7 @@ target_directory_operand (char const *file)
     (dereference_dest_dir_symlinks ? stat (file, &st) : lstat (file, &st));
   int err = (stat_result == 0 ? 0 : errno);
   bool is_a_dir = !err && S_ISDIR (st.st_mode);
-  if (err && err != ENOENT)
+  if (err && ! errno_nonexisting (errno))
     error (EXIT_FAILURE, err, _("failed to access %s"), quote (file));
   if (is_a_dir < looks_like_a_dir)
     error (EXIT_FAILURE, err, _("target %s is not a directory"), quote (file));
diff --git a/tests/ln/sf-1.sh b/tests/ln/sf-1.sh
index 3f4f8f1ae..17e67a9fb 100755
--- a/tests/ln/sf-1.sh
+++ b/tests/ln/sf-1.sh
@@ -20,12 +20,27 @@
 print_ver_ ln
 
 echo foo > a || framework_failure_
-ln -s . b || framework_failure_
 
+# Check that a target directory of '.' is supported
+# and that indirectly specifying the same target and link name
+# through that is detected.
+ln -s . b || framework_failure_
 ln -sf a b > err 2>&1 && fail=1
 case $(cat err) in
   *'are the same file') ;;
   *) fail=1 ;;
 esac
 
+# Ensure we replace symlinks that don't or can't link to an existing target.
+# coreutils-8.22 would fail to replace {ENOTDIR,ELOOP,ENAMETOOLONG}_link below.
+name_max_plus1=$(expr $(stat -f -c %l .) + 1)
+test $name_max_plus1 -gt 1 || skip_ 'Error determining NAME_MAX'
+long_name=$(printf '%0*d' $name_max_plus1 0)
+for f in '' f; do
+  ln -s$f missing ENOENT_link || fail=1
+  ln -s$f a/b ENOTDIR_link || fail=1
+  ln -s$f ELOOP_link ELOOP_link || fail=1
+  ln -s$f "$long_name" ENAMETOOLONG_link || fail=1
+done
+
 Exit $fail