scp: avoid double expansion of file

- Use `_comp_xfunc_ssh_scp_local_files` only for `-F` option.
- Otherwise use `_filedir` and add heuristics based on number of
  completion variants whether the argument is hostname or it is a local
  file, so a space should be appended.

Author: maxnikulin

completions/ssh

@@ -565,11 +565,10 @@ _scp()
             ;;
     esac
 
-    local prefix
-
     if [[ $cur == -F* ]]; then
         cur=${cur#-F}
-        prefix=-F
+        # _filedir will not add -F prefix
+        _comp_xfunc_ssh_scp_local_files -F
     else
         case $cur in
             -*)
@@ -579,17 +578,22 @@ _scp()
                 return
                 ;;
             */* | [.~]*)
-                # not a known host
-                _filedir
+                # not a known host, pass through
                 ;;
             *)
                 _known_hosts_real ${ipvx-} -c -a \
                     ${configfile:+-F "$configfile"} -- "$cur"
                 ;;
         esac
+        local count=${#COMPREPLY[@]}
+        # Keep "~" prefix.
+        _filedir
+        # Do not append space to known host.
+        if [ $count -ne ${#COMPREPLY[@]} ]; then
+            compopt +o nospace
+        fi
     fi
 
-    _comp_xfunc_ssh_scp_local_files "${prefix-}"
 } &&
     complete -F _scp -o nospace scp