fts: reduce two or more trailing slashes to just one, usually

* lib/fts.c (fts_open): Upon initialization, if a name ends in two
or more slashes, trim all but the final one.  But if a name consists
solely of two slashes, don't modify it.  If it consists solely of
three or more slashes, strip all but one.

This is part of the solution to a minor problem with rm:
it would print a bogus ELOOP diagnostic when failing to remove
the slash-decorated name of a symlink-to-directory:

    $ mkdir d && ln -s d s && env rm -r s/
    rm: cannot remove 's': Too many levels of symbolic links

With the change below and a trivial don't-trim-trailing-slashes
adjustment to remove.c, it does this:

    $ env rm -r s/
    rm: cannot remove 's/': Not a directory

Improved by: Eric Blake

2 files changed, 29 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index d4d2cb1051..0874c81464 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,26 @@
 2012-09-04  Jim Meyering  <meyering@redhat.com>
 
+	fts: reduce two or more trailing spaces to just one, usually
+	* lib/fts.c (fts_open): Upon initialization, if a name ends in two
+	or more slashes, trim all but the final one.  But if a name consists
+	solely of two slashes, don't modify it.  If it consists solely of
+	three or more slashes, strip all but one.
+
+	This is part of the solution to a minor problem with rm:
+	it would print a bogus ELOOP diagnostic when failing to remove
+	the slash-decorated name of a symlink-to-directory:
+
+	    $ mkdir d && ln -s d s && env rm -r s/
+	    rm: cannot remove 's': Too many levels of symbolic links
+
+	With the change below and a trivial don't-trim-trailing-slashes
+	adjustment to remove.c, it does this:
+
+	    $ env rm -r s/
+	    rm: cannot remove 's/': Not a directory
+
+	Improved by: Eric Blake
+
 	fts: when there is no risk of overlap, use memcpy, not memmove
 	* lib/fts.c (fts_alloc): Fix unjustified memcopy: s/memmove/memcpy/
 
diff --git a/lib/fts.c b/lib/fts.c
index ce14a807f8..36f7e0dda6 100644
--- a/lib/fts.c
+++ b/lib/fts.c
@@ -487,6 +487,14 @@ fts_open (char * const *argv,
         for (root = NULL, nitems = 0; *argv != NULL; ++argv, ++nitems) {
                 /* *Do* allow zero-length file names. */
                 size_t len = strlen(*argv);
+
+                /* If there are two or more trailing slashes, trim all but one,
+                   but don't change "//" to "/", and do map "///" to "/".  */
+                char const *v = *argv;
+                if (2 < len && v[len - 1] == '/')
+                  while (1 < len && v[len - 2] == '/')
+                    --len;
+
                 if ((p = fts_alloc(sp, *argv, len)) == NULL)
                         goto mem3;
                 p->fts_level = FTS_ROOTLEVEL;