change-nth: empty value restores default --nth

- Same rule as change-with-nth and transform-with-nth
    - Empty: default
    - '..': all fields
    - Non-empty invalid: ignored
- Previously, change-nth() and empty transform-nth output searched
  all fields, and transform-nth could not restore default
- Partly reverts af0014ab. Use change-nth(..) to unset default

CHANGELOG.md

@@ -9,7 +9,9 @@ CHANGELOG
     - Only `change-nth` and `change-with-nth` rotate through `|`-separated values
     - Fixed the bound command being replaced with the output. e.g. With `transform-nth(echo '1|2')`, the next key press ran `2|1` as a shell command.
     - A `--with-nth` template in the output can now contain `|`. e.g. `{2}|{1}` was cut to `{2}`.
-- An invalid value for `change-nth` and `transform-nth` no longer restores the default `--nth`. It is ignored, as with `change-with-nth` and `transform-with-nth`.
+- `change-nth` and `transform-nth` now handle empty and invalid values the same way as `change-with-nth` and `transform-with-nth`
+    - An empty value restores the default `--nth`. Previously, `change-nth()` and an empty `transform-nth` output searched all fields. Use `change-nth(..)` for that.
+    - A non-empty invalid value is ignored. Previously, it restored the default `--nth`.
 - `change-nth` and `change-with-nth` now apply the value after the current one in the `|`-separated list
     - A value equal to the current one is skipped, e.g. the first value when it is the initial `--nth`
     - Invalid values in the list are skipped

man/man1/fzf.1

@@ -2060,8 +2060,8 @@ A key or an event can be bound to one or more of the following actions.
     \fBchange\-list\-label(...)\fR       (change \fB\-\-list\-label\fR to the given string)
     \fBchange\-multi\fR                 (enable multi-select mode with no limit)
     \fBchange\-multi(...)\fR            (enable multi-select mode with a limit or disable it with 0)
-    \fBchange\-nth(...)\fR              (change \fB\-\-nth\fR option; rotate through the multiple options separated by '|', starting from the one after the current option)
-    \fBchange\-with\-nth(...)\fR         (change \fB\-\-with\-nth\fR option; rotate through the multiple options separated by '|', starting from the one after the current option)
+    \fBchange\-nth(...)\fR              (change \fB\-\-nth\fR option; see CHANGE NTH AND WITH\-NTH)
+    \fBchange\-with\-nth(...)\fR         (change \fB\-\-with\-nth\fR option; see CHANGE NTH AND WITH\-NTH)
     \fBchange\-pointer(...)\fR          (change \fB\-\-pointer\fR option)
     \fBchange\-preview(...)\fR          (change \fB\-\-preview\fR option)
     \fBchange\-preview\-label(...)\fR    (change \fB\-\-preview\-label\fR to the given string)
@@ -2166,8 +2166,8 @@ A key or an event can be bound to one or more of the following actions.
     \fBtransform\-header\-label(...)\fR  (transform header label using an external command)
     \fBtransform\-input\-label(...)\fR   (transform input label using an external command)
     \fBtransform\-list\-label(...)\fR    (transform list label using an external command)
-    \fBtransform\-nth(...)\fR           (transform nth using an external command; no rotation, output is used as a whole)
-    \fBtransform\-with\-nth(...)\fR      (transform with-nth using an external command; no rotation, output is used as a whole)
+    \fBtransform\-nth(...)\fR           (transform nth using an external command; see CHANGE NTH AND WITH\-NTH)
+    \fBtransform\-with\-nth(...)\fR      (transform with-nth using an external command; see CHANGE NTH AND WITH\-NTH)
     \fBtransform\-pointer(...)\fR       (transform pointer using an external command)
     \fBtransform\-preview\-label(...)\fR (transform preview label using an external command)
     \fBtransform\-prompt(...)\fR        (transform prompt string using an external command)
@@ -2405,6 +2405,28 @@ e.g.
      # This is equivalent to toggle\-preview action
      fzf \-\-preview 'cat {}' \-\-bind 'ctrl\-/:change\-preview\-window(hidden|)'
 
+.SS CHANGE NTH AND WITH\-NTH
+
+\fBchange\-nth\fR and \fBchange\-with\-nth\fR actions change \fB\-\-nth\fR and
+\fB\-\-with\-nth\fR options. You can specify multiple values separated by '|'
+characters. Each time the action runs, fzf applies the value after the current
+one in the list, skipping the values equal to the current one.
+
+\fBtransform\-nth\fR and \fBtransform\-with\-nth\fR actions (and their
+\fBbg\-\fR variants) take the output of the command as a single value. The
+following rules apply to all of these actions.
+
+    * An empty value restores the default given by the option
+    * \fB..\fR selects all fields
+    * A non\-empty invalid value is ignored
+
+e.g.
+     # All fields, then fields 1, 2, and 3
+     fzf \-\-bind 'ctrl\-/:change\-nth(..|1|2|3)'
+
+     # An empty string in the list is interpreted as the default
+     fzf \-\-nth 1 \-\-bind 'ctrl\-/:change\-nth(2|)'
+
 .SH AUTHOR
 Junegunn Choi (\fIjunegunn.c@gmail.com\fR)
 

src/terminal.go

@@ -7341,18 +7341,15 @@ func (t *Terminal) Loop() error {
 				req(reqList, reqInfo)
 			case actChangeNth, actTransformNth, actBgTransformNth:
 				capture(true, func(expr string) {
-					empty := len(expr) == 0
-					// Empty value means all fields if it is the whole
-					// expression, otherwise the default --nth
 					resolve := func(value string) ([]Range, bool) {
-						if nth, err := splitNth(value); err == nil || empty {
-							return nth, true
-						} else if len(value) == 0 {
+						// Empty value restores the default --nth
+						if len(value) == 0 {
 							return t.nth, true
 						}
-						return nil, false
+						nth, err := splitNth(value)
+						return nth, err == nil
 					}
-					// Empty or a single '..' means all fields
+					// Empty range list or a single '..' means all fields
 					allFields := func(nth []Range) bool {
 						return len(nth) == 0 || len(nth) == 1 && nth[0].IsFull()
 					}

test/test_core.rb

@@ -3033,7 +3033,7 @@ class TestCore < TestInteractive
   end
 
   def test_change_nth_unset_default
-    tmux.send_keys %(echo foo bar | #{FZF} --nth 2 --query fb --bind space:change-nth:), :Enter
+    tmux.send_keys %(echo foo bar | #{FZF} --nth 2 --query fb --bind space:change-nth:..), :Enter
     tmux.until do
       assert_equal 1, it.item_count
       assert_equal 0, it.match_count
@@ -3047,6 +3047,19 @@ class TestCore < TestInteractive
     end
   end
 
+  def test_change_nth_empty_restores_default
+    tmux.send_keys %(echo foo bar | #{FZF} --nth 2 --query fb --bind 'a:change-nth(..),space:change-nth(),b:transform-nth(true)'), :Enter
+    tmux.until { |lines| assert_equal 0, lines.match_count }
+    tmux.send_keys :a
+    tmux.until { |lines| assert_equal 1, lines.match_count }
+    tmux.send_keys :Space
+    tmux.until { |lines| assert_equal 0, lines.match_count }
+    tmux.send_keys :a
+    tmux.until { |lines| assert_equal 1, lines.match_count }
+    tmux.send_keys :b
+    tmux.until { |lines| assert_equal 0, lines.match_count }
+  end
+
   def test_change_header_lines
     tmux.send_keys %(seq 10 | #{FZF} --header-lines 3 --bind 'space:change-header-lines(5),enter:transform-header-lines(echo 1)'), :Enter
     tmux.until do |lines|