Add 'start' event that is triggered once when fzf finder starts

Close #1622

CHANGELOG.md

@@ -1,6 +1,15 @@
 CHANGELOG
 =========
 
+0.35.0
+------
+- Added `start` event that is triggered only once when fzf finder starts.
+  Since fzf consumes the input stream asynchronously, the input list is not
+  available unless you use `--sync`.
+  ```sh
+  seq 100 | fzf --multi --sync --bind 'start:last+select-all+preview(echo welcome)'
+  ```
+
 0.34.0
 ------
 - Added support for adaptive `--height`. If the `--height` value is prefixed

man/man1/fzf.1

@@ -21,7 +21,7 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 ..
-.TH fzf 1 "Sep 2022" "fzf 0.34.0" "fzf - a command-line fuzzy finder"
+.TH fzf 1 "Oct 2022" "fzf 0.35.0" "fzf - a command-line fuzzy finder"
 
 .SH NAME
 fzf - a command-line fuzzy finder
@@ -811,6 +811,15 @@ e.g.
 or any single character
 
 .SS AVAILABLE EVENTS:
+\fIstart\fR
+.RS
+Triggered only once when fzf finder starts. Since fzf consumes the input stream
+asynchronously, the input list is not available unless you use \fI--sync\fR.
+
+e.g.
+     \fB# Move cursor to the last item and select all items
+     seq 1000 | fzf --multi --sync --bind start:last+select-all\fR
+.RE
 \fIchange\fR
 .RS
 Triggered whenever the query string is changed

src/options.go

@@ -543,6 +543,8 @@ func parseKeyChords(str string, message string) map[tui.Event]string {
 			add(tui.Change)
 		case "backward-eof":
 			add(tui.BackwardEOF)
+		case "start":
+			add(tui.Start)
 		case "alt-enter", "alt-return":
 			chords[tui.CtrlAltKey('m')] = key
 		case "alt-space":

src/terminal.go

@@ -2362,13 +2362,21 @@ func (t *Terminal) Loop() {
 	}()
 
 	looping := true
+	_, startEvent := t.keymap[tui.Start.AsEvent()]
+
 	for looping {
 		var newCommand *string
 		changed := false
 		beof := false
 		queryChanged := false
 
-		event := t.tui.GetChar()
+		var event tui.Event
+		if startEvent {
+			event = tui.Start.AsEvent()
+			startEvent = false
+		} else {
+			event = t.tui.GetChar()
+		}
 
 		t.mutex.Lock()
 		previousInput := t.input

src/tui/tui.go

@@ -90,6 +90,7 @@ const (
 
 	Change
 	BackwardEOF
+	Start
 
 	AltBS
 

test/test_go.rb

@@ -2332,6 +2332,14 @@ def test_height_range_overflow
     OUTPUT
     tmux.until { assert_block(expected, _1) }
   end
+
+  def test_start_event
+    tmux.send_keys 'seq 100 | fzf --multi --sync --preview-window border-none --bind "start:select-all+last+preview(echo welcome)"', :Enter
+    tmux.until do |lines|
+      assert_match(/>100.*welcome/, lines[0])
+      assert_includes(lines[-2], '100/100 (100)')
+    end
+  end
 end
 
 module TestShell