Do not start the initial reader if 'reload*' is bound to 'start'

CHANGELOG.md

@@ -32,6 +32,15 @@ CHANGELOG
   fzf --listen --sync --bind 'focus:transform-header:curl -s localhost:$FZF_PORT?limit=0 | jq .'
   ```
 - Added `offset-middle` action to place the current item is in the middle of the screen
+- fzf will not start the initial reader when `reload` or `reload-sync` is bound to `start` event. `fzf < /dev/null` or `: | fzf` are no longer required and extraneous `load` event will not fire due to the empty list.
+  ```sh
+  # Now this will work as expected. Previously, this would print an invalid header line.
+  # `fzf < /dev/null` or `: | fzf` would fix the problem, but then an extraneous 
+  # `load` event would fire and the header would be prematurely updated.
+  fzf --header 'Loading ...' --header-lines 1 \
+      --bind 'start:reload:sleep 1; ps -ef' \
+      --bind 'load:change-header:Loaded!'
+  ```
 - Fixed mouse support on Windows
 - Fixed crash when using `--tiebreak=end` with very long items
 - zsh 5.0 compatibility (thanks to @LangLangBart)

src/constants.go

@@ -58,6 +58,7 @@ const (
 const (
 	EvtReadNew util.EventType = iota
 	EvtReadFin
+	EvtReadNone
 	EvtSearchNew
 	EvtSearchProgress
 	EvtSearchFin

src/core.go

@@ -147,14 +147,21 @@ func Run(opts *Options) (int, error) {
 	executor := util.NewExecutor(opts.WithShell)
 
 	// Reader
+	reloadOnStart := opts.reloadOnStart()
 	streamingFilter := opts.Filter != nil && !sort && !opts.Tac && !opts.Sync
 	var reader *Reader
 	if !streamingFilter {
 		reader = NewReader(func(data []byte) bool {
 			return chunkList.Push(data)
 		}, eventBox, executor, opts.ReadZero, opts.Filter == nil)
+
+		if reloadOnStart {
+			// reload or reload-sync action is bound to 'start' event, no need to start the reader
+			eventBox.Set(EvtReadNone, nil)
+		} else {
 			go reader.ReadSource(opts.Input, opts.WalkerRoot, opts.WalkerOpts, opts.WalkerSkip)
 		}
+	}
 
 	// Matcher
 	forward := true
@@ -227,7 +234,8 @@ func Run(opts *Options) (int, error) {
 	}
 
 	// Synchronous search
-	if opts.Sync {
+	sync := opts.Sync && !reloadOnStart
+	if sync {
 		eventBox.Unwatch(EvtReadNew)
 		eventBox.WaitFor(EvtReadFin)
 	}
@@ -247,7 +255,7 @@ func Run(opts *Options) (int, error) {
 	if heightUnknown {
 		maxFit, padHeight = terminal.MaxFitAndPad()
 	}
-	deferred := opts.Select1 || opts.Exit0 || opts.Sync
+	deferred := opts.Select1 || opts.Exit0 || sync
 	go terminal.Loop()
 	if !deferred && !heightUnknown {
 		// Start right away
@@ -314,6 +322,9 @@ func Run(opts *Options) (int, error) {
 					err = quitSignal.err
 					stop = true
 					return
+				case EvtReadNone:
+					reading = false
+					terminal.UpdateCount(0, false, nil)
 				case EvtReadNew, EvtReadFin:
 					if evt == EvtReadFin && nextCommand != nil {
 						restart(*nextCommand, nextEnviron)

src/options.go

@@ -2945,3 +2945,18 @@ func ParseOptions(useDefaults bool, args []string) (*Options, error) {
 
 	return opts, nil
 }
+
+func (opts *Options) reloadOnStart() bool {
+	// Not compatible with --filter
+	if opts.Filter != nil {
+		return false
+	}
+	if actions, prs := opts.Keymap[tui.Start.AsEvent()]; prs {
+		for _, action := range actions {
+			if action.t == actReload || action.t == actReloadSync {
+				return true
+			}
+		}
+	}
+	return false
+}

test/test_go.rb

@@ -26,12 +26,12 @@ BASE = File.expand_path('..', __dir__)
 Dir.chdir(BASE)
 FZF = "FZF_DEFAULT_OPTS=\"--no-scrollbar --pointer \\> --marker \\>\" FZF_DEFAULT_COMMAND= #{BASE}/bin/fzf"
 
-def wait
+def wait(timeout = DEFAULT_TIMEOUT)
   since = Time.now
   begin
     yield or raise Minitest::Assertion, 'Assertion failure'
   rescue Minitest::Assertion
-    raise if Time.now - since > DEFAULT_TIMEOUT
+    raise if Time.now - since > timeout
 
     sleep(0.05)
     retry
@@ -103,10 +103,10 @@ class Tmux
     go(%W[capture-pane -p -J -t #{win}]).map(&:rstrip).reverse.drop_while(&:empty?).reverse
   end
 
-  def until(refresh = false)
+  def until(refresh = false, timeout: DEFAULT_TIMEOUT)
     lines = nil
     begin
-      wait do
+      wait(timeout) do
         lines = capture
         class << lines
           def counts
@@ -3356,6 +3356,14 @@ class TestGoFZF < TestBase
     BLOCK
     tmux.until { assert_block(block, _1) }
   end
+
+  def test_start_on_reload
+    tmux.send_keys %[echo foo | #{FZF} --header Loading --header-lines 1 --bind 'start:reload:sleep 2; echo bar' --bind 'load:change-header:Loaded'], :Enter
+    tmux.until(timeout: 1) { |lines| assert_includes lines[-3], 'Loading' }
+    tmux.until(timeout: 1) { |lines| refute_includes lines[-4], 'foo' }
+    tmux.until { |lines| assert_includes lines[-3], 'Loaded' }
+    tmux.until { |lines| assert_includes lines[-4], 'bar' }
+  end
 end
 
 module TestShell