libexec/rbenv: do not cd for path without dir

Without this patch you would see the following error for a symlink like
"/usr/bin/asciidoc -> asciidoc.py":

> …/libexec/{py,rb}env: line 43: cd: asciidoc.py: Not a directory

Ref: sstephenson/bats#224
Ref: pyenv/pyenv#689
Closes: rbenv#868

libexec/rbenv

@@ -36,17 +36,23 @@ else
   }
 
   abs_dirname() {
-    local cwd="$PWD"
     local path="$1"
-
-    while [ -n "$path" ]; do
-      cd "${path%/*}"
-      local name="${path##*/}"
+    local save_cwd="$PWD"
+    local dir name
+
+    while [[ -n "$path" ]]; do
+      dir="${path%/*}"
+      if [[ "$dir" != "$path" ]]; then
+        cd "$dir"
+        name="${path##*/}"
+      else
+        name="$path"
+      fi
       path="$(resolve_link "$name" || true)"
     done
 
-    pwd
-    cd "$cwd"
+    echo "$PWD"
+    cd "$save_cwd"
   }
 fi
 

test/rbenv.bats

@@ -74,3 +74,12 @@ load test_helper
   run rbenv echo "RBENV_HOOK_PATH"
   assert_success "${RBENV_ROOT}/rbenv.d:${BATS_TEST_DIRNAME%/*}/rbenv.d:/usr/local/etc/rbenv.d:/etc/rbenv.d:/usr/lib/rbenv/hooks"
 }
+
+@test "abs_dirname with symlink in same dir" {
+  mkdir -p "$RBENV_TEST_DIR"
+  cd "$RBENV_TEST_DIR"
+  ln -s $(which rbenv) rbenv-wrapper
+  ln -s rbenv-wrapper rbenv-wrapper-link
+  run ./rbenv-wrapper-link echo "PATH"
+  assert_success "${BATS_TEST_DIRNAME%/*}/libexec:$PATH"
+}