[bash-completion] Fix custom completion with dynamic loader enabled

After _completion_loader is called, instead of loading the entire
completion.bash file, just restore the fzf completion for the current
command. `_fzf_orig_completion_$cmd` is only set if _completion_loader
actually changed the completion options to avoid infinite loop.

Close #1170

shell/completion.bash

@@ -113,7 +113,7 @@ _fzf_opts_completion() {
 }
 
 _fzf_handle_dynamic_completion() {
-  local cmd orig_var orig ret orig_cmd
+  local cmd orig_var orig ret orig_cmd orig_complete
   cmd="$1"
   shift
   orig_cmd="$1"
@@ -122,10 +122,14 @@ _fzf_handle_dynamic_completion() {
   if [ -n "$orig" ] && type "$orig" > /dev/null 2>&1; then
     $orig "$@"
   elif [ -n "$_fzf_completion_loader" ]; then
+    orig_complete=$(complete -p "$cmd")
     _completion_loader "$@"
     ret=$?
+    # _completion_loader may not have updated completion for the command
+    if [ "$(complete -p "$cmd")" != "$orig_complete" ]; then
       eval "$(complete | command grep "\-F.* $orig_cmd$" | _fzf_orig_completion_filter)"
-    source "${BASH_SOURCE[0]}"
+      eval "$orig_complete"
+    fi
     return $ret
   fi
 }

test/test_go.rb

@@ -1761,6 +1761,27 @@ class TestBash < TestBase
     super
     @tmux = Tmux.new :bash
   end
+
+  def test_dynamic_completion_loader
+    tmux.paste 'touch /tmp/foo; _fzf_completion_loader=1'
+    tmux.paste '_completion_loader() { complete -o default fake; }'
+    tmux.paste 'complete -F _fzf_path_completion -o default -o bashdefault fake'
+    tmux.send_keys 'fake /tmp/foo**', :Tab
+    tmux.until do |lines|
+      lines.item_count.positive? && lines.item_count == lines.match_count
+    end
+    tmux.send_keys 'C-c'
+
+    tmux.prepare
+    tmux.send_keys 'fake /tmp/foo'
+    tmux.send_keys :Tab , 'C-u'
+
+    tmux.prepare
+    tmux.send_keys 'fake /tmp/foo**', :Tab
+    tmux.until do |lines|
+      lines.item_count.positive? && lines.item_count == lines.match_count
+    end
+  end
 end
 
 class TestZsh < TestBase