Add bg-cancel action to ignore running background transforms

Close #4430

Example:

  # Implement popup that disappears after 1 second
  #   * Use footer as the popup
  #   * Use `bell` to ring the terminal bell
  #   * Use `bg-transform-footer` to clear the footer after 1 second
  #   * Use `bg-cancel` to ignore currently running background transform actions
  fzf --multi --list-border \
      --bind 'enter:execute-silent(echo -n {+} | pbcopy)+bell' \
      --bind 'enter:+transform-footer(echo Copied {} to clipboard)' \
      --bind 'enter:+bg-cancel+bg-transform-footer(sleep 1)'

1 files changed, 17 insertions, 0 deletions

diff --git a/test/test_core.rb b/test/test_core.rb
index f714e1c3..b7eba741 100644
--- a/test/test_core.rb
+++ b/test/test_core.rb
@@ -1964,4 +1964,21 @@ class TestCore < TestInteractive
     elapsed = Time.now - time
     assert elapsed < 2
   end
+
+  def test_bg_cancel
+    tmux.send_keys %(seq 0 1 | #{FZF} --bind 'space:bg-cancel+bg-transform-header(sleep {}; echo [{}])'), :Enter
+    tmux.until { assert_equal 2, it.match_count }
+    tmux.send_keys '1'
+    tmux.until { assert_equal 1, it.match_count }
+    tmux.send_keys :Space
+    tmux.send_keys :BSpace
+    tmux.until { assert_equal 2, it.match_count }
+    tmux.send_keys :Space
+    tmux.until { |lines| assert lines.any_include?('[0]') }
+    sleep 2
+    tmux.until do |lines|
+      assert lines.any_include?('[0]')
+      refute lines.any_include?('[1]')
+    end
+  end
 end