Add gocui primitives to block input during an operation

Long-running operations that lazygit drives itself (rebases, and the
commit surgery built on them) can be corrupted by keys the user presses
while they run: pressing e to start an interactive rebase, then up+d
before it finishes, must act on the resulting todo list, not race the
rebase. WithWaitingStatusSync gets this today only as a side effect of
freezing the UI thread, which the rest of this branch is moving away
from.

Add a nestable counter, BeginBlockingEvents/EndBlockingEvents, that
withholds input at the event-dispatch layer without freezing anything:
while blocked, key events are buffered and replayed in order once the
count returns to zero (so they act on the now-current context), mouse
clicks and hover are dropped (replaying them against a changed layout
would target the wrong thing), and scrolling, resize, focus and all
rendering keep flowing. These are the reusable core; a gui-level helper
that brackets them around a worker operation follows.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pkg/gocui/block_events_test.go

@@ -0,0 +1,98 @@
+package gocui
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestEventWithheldWhileBlocking(t *testing.T) {
+	scenarios := []struct {
+		name     string
+		event    GocuiEvent
+		withheld bool
+	}{
+		{"key", GocuiEvent{Type: eventKey, Key: NewKeyRune('x')}, true},
+		{"mouse click", GocuiEvent{Type: eventMouse, Key: NewKeyName(MouseLeft)}, true},
+		{"mouse scroll", GocuiEvent{Type: eventMouse, Key: NewKeyName(MouseWheelDown)}, false},
+		{"mouse move", GocuiEvent{Type: eventMouseMove}, true},
+		{"resize", GocuiEvent{Type: eventResize}, false},
+		{"focus", GocuiEvent{Type: eventFocus}, false},
+		{"paste", GocuiEvent{Type: eventPaste}, false},
+		{"error", GocuiEvent{Type: eventError}, false},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			assert.Equal(t, s.withheld, eventWithheldWhileBlocking(&s.event))
+		})
+	}
+}
+
+// setupKeyRecorder wires a keybinding on a focused view that records each time
+// it fires, and returns the key event that triggers it plus the record slice.
+func setupKeyRecorder(t *testing.T, g *Gui) (GocuiEvent, *[]int) {
+	t.Helper()
+
+	_, _ = g.SetView("main", 0, 0, 80, 22, 0)
+	_, err := g.SetCurrentView("main")
+	assert.NoError(t, err)
+
+	fired := []int{}
+	callCount := 0
+	key := NewKeyRune('x')
+	g.SetKeybinding("main", key, func(*Gui, *View) error {
+		callCount++
+		fired = append(fired, callCount)
+		return nil
+	})
+
+	return GocuiEvent{Type: eventKey, Key: key}, &fired
+}
+
+func TestBlockingEvents_KeysBufferedAndReplayed(t *testing.T) {
+	g := newTestGui(t)
+	keyEvent, fired := setupKeyRecorder(t, g)
+
+	// Not blocking: the key dispatches immediately.
+	assert.NoError(t, g.handleEvent(&keyEvent))
+	assert.Len(t, *fired, 1)
+
+	// While blocking: the key is buffered, not dispatched.
+	g.BeginBlockingEvents()
+	assert.NoError(t, g.handleEvent(&keyEvent))
+	assert.NoError(t, g.handleEvent(&keyEvent))
+	assert.Len(t, *fired, 1, "buffered keys must not dispatch while blocking")
+
+	// Unblocking replays the buffered keys.
+	assert.NoError(t, g.EndBlockingEvents())
+	assert.Len(t, *fired, 3, "both buffered keys should replay on unblock")
+	assert.Empty(t, g.bufferedKeyEvents)
+}
+
+func TestBlockingEvents_NestsWithCounter(t *testing.T) {
+	g := newTestGui(t)
+	keyEvent, fired := setupKeyRecorder(t, g)
+
+	g.BeginBlockingEvents()
+	g.BeginBlockingEvents()
+	assert.NoError(t, g.handleEvent(&keyEvent))
+
+	// The inner block ending still leaves us blocked: no replay yet.
+	assert.NoError(t, g.EndBlockingEvents())
+	assert.Empty(t, *fired)
+
+	// Only the outermost block ending replays.
+	assert.NoError(t, g.EndBlockingEvents())
+	assert.Len(t, *fired, 1)
+}
+
+func TestBlockingEvents_MouseClicksDroppedNotBuffered(t *testing.T) {
+	g := newTestGui(t)
+
+	g.BeginBlockingEvents()
+	click := GocuiEvent{Type: eventMouse, Key: NewKeyName(MouseLeft)}
+	assert.NoError(t, g.handleEvent(&click))
+	assert.Empty(t, g.bufferedKeyEvents, "mouse clicks must be dropped, not buffered")
+	assert.NoError(t, g.EndBlockingEvents())
+}

pkg/gocui/gui.go

@@ -210,6 +210,14 @@ type Gui struct {
 	// MainLoop starts. IsUIThread compares against it. Written once, read from
 	// worker goroutines, so it's atomic.
 	uiThreadID atomic.Int64
+
+	// blockInputCount, when greater than zero, withholds keyboard input from
+	// the handlers: key events are buffered into bufferedKeyEvents and replayed
+	// once the count drops back to zero, while mouse clicks and hover are
+	// dropped outright. It's a counter so blocking can nest. Both fields are
+	// only touched on the UI thread. See BeginBlockingEvents.
+	blockInputCount   int
+	bufferedKeyEvents []GocuiEvent
 }
 
 type NewGuiOpts struct {
@@ -806,6 +814,42 @@ func (g *Gui) IsUIThread() bool {
 	return goid.Get() == g.uiThreadID.Load()
 }
 
+// BeginBlockingEvents starts withholding keyboard input from the handlers, so a
+// long-running operation can't be disrupted by keys the user presses while it
+// runs. Keys are buffered and replayed once EndBlockingEvents balances this
+// call; mouse clicks and hover are dropped for the duration. Scrolling,
+// resizing, focus changes and all rendering keep working throughout. It's a
+// counter, so blocking nests; every call must be paired with EndBlockingEvents.
+//
+// Must be called on the UI thread. Callers arrange this by beginning the block
+// synchronously from the keybinding handler, before dispatching the operation
+// to a worker — beginning it from the worker would race the next queued
+// keypress, which is exactly the input we mean to withhold.
+func (g *Gui) BeginBlockingEvents() {
+	g.blockInputCount++
+}
+
+// EndBlockingEvents balances a BeginBlockingEvents call. When the last nested
+// block ends, the keys buffered while blocked are replayed in order through the
+// normal dispatch path, so they act on the now-current context (a key whose
+// binding no longer exists is simply ignored, just as if it had been pressed
+// now). Must be called on the UI thread.
+func (g *Gui) EndBlockingEvents() error {
+	g.blockInputCount--
+	if g.blockInputCount > 0 {
+		return nil
+	}
+
+	buffered := g.bufferedKeyEvents
+	g.bufferedKeyEvents = nil
+	for i := range buffered {
+		if err := g.handleEvent(&buffered[i]); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // OnUIThreadAndWait runs f on the main event-loop goroutine and blocks the
 // caller until f has run, returning f's error. Use it to read UI-thread-owned
 // state (the model, contexts) from a worker without racing the UI thread.
@@ -1052,6 +1096,17 @@ func (g *Gui) processRemainingEvents() (bool, error) {
 // handleEvent handles an event, based on its type (key-press, error,
 // etc.)
 func (g *Gui) handleEvent(ev *GocuiEvent) error {
+	if g.blockInputCount > 0 && eventWithheldWhileBlocking(ev) {
+		if ev.Type == eventKey {
+			// Buffer keys so they replay against fresh state on unblock.
+			g.bufferedKeyEvents = append(g.bufferedKeyEvents, *ev)
+		}
+		// Mouse clicks and hover fall through to here without being buffered:
+		// replaying them once the operation has changed the layout underneath
+		// them would target the wrong thing, so we drop them outright.
+		return nil
+	}
+
 	switch ev.Type {
 	case eventKey, eventMouse, eventMouseMove:
 		return g.onKey(ev)
@@ -1070,6 +1125,24 @@ func (g *Gui) handleEvent(ev *GocuiEvent) error {
 	}
 }
 
+// eventWithheldWhileBlocking reports whether an event must not reach the
+// handlers while input is blocked (see BeginBlockingEvents). Key events are
+// withheld (buffered for replay); mouse clicks and hover are withheld (dropped).
+// Everything else — mouse scrolling, resize, focus, paste, errors — flows
+// through as usual.
+func eventWithheldWhileBlocking(ev *GocuiEvent) bool {
+	switch ev.Type {
+	case eventKey:
+		return true
+	case eventMouse:
+		return !IsMouseScrollKey(ev.Key.KeyName())
+	case eventMouseMove:
+		return true
+	default:
+		return false
+	}
+}
+
 func (g *Gui) onResize() {
 	// not sure if we actually need this
 	// g.screen.Sync()