ui/text: replace Editor.Update with Next for stepping through events

Before this change, the Editor cleared its content after each
Submission event. If it didn't multiple submits for a frame would
not result in the cleared text for clients that wants to clear the
Editor between submits.

However, for clients that do not want to clear the content or that
wants to validate the text before accepting it were not supported.

Instead, switch to a event stepping model, where the client can
call Next to receive each EditorEvent (that is, Submit event) in
turn.

We can then delete the Submit flag on Editor and always report Submit
events.

We can also make Layout flush the pending events now that Editor
always has access to its Config and input queue.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/text/editor.go

@@ -25,7 +25,6 @@ type Editor struct {
 	Face       Face
 	Alignment  Alignment
 	SingleLine bool
-	Submit     bool
 
 	oldCfg            ui.Config
 	blinkStart        time.Time
@@ -56,18 +55,16 @@ type EditorEvent interface {
 	isEditorEvent()
 }
 
-type Submission struct {
-	Text string
-}
+type Submit struct{}
 
 const (
 	blinksPerSecond  = 1
 	maxBlinkDuration = 10 * time.Second
 )
 
-func (s Submission) isEditorEvent() {}
+func (s Submit) isEditorEvent() {}
 
-func (e *Editor) Update() []EditorEvent {
+func (e *Editor) Next() (EditorEvent, bool) {
 	if cfg := *e.Config; cfg != e.oldCfg {
 		e.invalidate()
 		e.oldCfg = cfg
@@ -106,7 +103,6 @@ func (e *Editor) Update() []EditorEvent {
 		}
 	}
 	stop := (sdist > 0 && soff >= smax) || (sdist < 0 && soff <= smin)
-	var events []EditorEvent
 	for _, ke := range e.Inputs.For(e) {
 		e.blinkStart = e.Config.Now
 		switch ke := ke.(type) {
@@ -116,11 +112,9 @@ func (e *Editor) Update() []EditorEvent {
 			if !e.focused {
 				break
 			}
-			if e.Submit && (ke.Name == key.NameReturn || ke.Name == key.NameEnter) {
+			if ke.Name == key.NameReturn || ke.Name == key.NameEnter {
 				if !ke.Modifiers.Contain(key.ModShift) {
-					events = append(events, Submission{e.Text()})
-					e.SetText("")
-					break
+					return Submit{}, true
 				}
 			}
 			if e.command(ke) {
@@ -139,7 +133,7 @@ func (e *Editor) Update() []EditorEvent {
 	if stop {
 		e.scroller.Stop()
 	}
-	return events
+	return nil, false
 }
 
 func (e *Editor) caretWidth() fixed.Int26_6 {
@@ -148,6 +142,11 @@ func (e *Editor) caretWidth() fixed.Int26_6 {
 }
 
 func (e *Editor) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
+	for {
+		if _, ok := e.Next(); !ok {
+			break
+		}
+	}
 	twoDp := int(e.Config.Val(ui.Dp(2)) + 0.5)
 	e.padLeft, e.padRight = twoDp, twoDp
 	maxWidth := cs.Width.Max