realpath: remove extraneous '/' for --relative-to edge cases

* src/realpath.c (path_common_prefix): Be consistent and
always include a leading '/' in the count returned.
(relpath): Account for the change in path_common_prefix()
and avoid outputting extra '/' chars in relative paths that
span the root dir.
* tests/misc/realpath: Add the two reported cases.
Reported by Mike Frysinger

1 files changed, 8 insertions, 3 deletions

diff --git a/tests/misc/realpath b/tests/misc/realpath
index fb0139367..8a1f336cd 100755
--- a/tests/misc/realpath
+++ b/tests/misc/realpath
@@ -41,13 +41,18 @@ realpath -m '' && fail=1
 
 # symlink resolution
 this=$(realpath .)
-test "$(realpath $relative ldir2/..)" = "$this/dir1" || fail=1
-test "$(realpath -L $relative ldir2/..)" = "$this" || fail=1
-test "$(realpath -s $relative ldir2)" = "$this/ldir2" || fail=1
+test "$(realpath ldir2/..)" = "$this/dir1" || fail=1
+test "$(realpath -L ldir2/..)" = "$this" || fail=1
+test "$(realpath -s ldir2)" = "$this/ldir2" || fail=1
 
 # relative string handling
 test $(realpath -m --relative-to=prefix prefixed/1) = '../prefixed/1' || fail=1
 test $(realpath -m --relative-to=prefixed prefix/1) = '../prefix/1' || fail=1
 test $(realpath -m --relative-to=prefixed prefixed/1) = '1' || fail=1
 
+# Ensure no redundant trailing '/' present, as was the case in v8.15
+test $(realpath -sm --relative-to=/usr /) = '..' || fail=1
+# Ensure no redundant leading '../' present, as was the case in v8.15
+test $(realpath -sm --relative-to=/ /usr) = 'usr' || fail=1
+
 Exit $fail