more changes to better handle undef vars

This is only needed if we make undefined vars an error as proposed in
issue #4163 but it's a good idea anyway.

share/functions/cd.fish

@@ -31,6 +31,8 @@ function cd --description "Change directory"
     set -l cd_status $status
 
     if test $cd_status -eq 0 -a "$PWD" != "$previous"
+        set -q dirprev
+        or set -l dirprev
         set -q dirprev[$MAX_DIR_HIST]
         and set -e dirprev[1]
         set -g dirprev $dirprev $previous

share/functions/popd.fish

@@ -8,12 +8,11 @@ function popd --description "Pop directory from the stack and cd to it"
         end
     end
 
-    if test $dirstack[1]
+    if set -q dirstack[1]
         cd $dirstack[1]
+        set -e dirstack[1]
     else
         printf (_ "%s: Directory stack is empty…\n") popd 1>&2
         return 1
     end
-
-    set -e dirstack[1]
 end

share/functions/pushd.fish

@@ -18,10 +18,13 @@ function pushd --description 'Push directory to stack'
         end
     end
 
+    set -q dirstack
+    or set -g dirstack
+
     # emulate bash: an empty pushd should switch the top of dirs
-    if test (count $argv) -eq 0
+    if not set -q argv[1]
         # check that the stack isn't empty
-        if test (count $dirstack) -eq 0
+        if not set -q dirstack[1]
             echo "pushd: no other directory"
             return 1
         end

tests/test.fish

@@ -24,7 +24,10 @@ end
 set TERM xterm
 set -e ITERM_PROFILE
 
-source test_util.fish (status -f) $argv; or exit
+set -q argv
+or set argv
+source test_util.fish (status -f) $argv
+or exit
 
 say -o cyan "Testing high level script functionality"