app,io/router: expand IME snippets if a new range overlaps the old

Instead of cmpletely replacing the IME snippet for every update, expand
the old range if there is overlap. This change avoids never-ending
restarts of the IME on Android where snippets are expanded in two
calls, one for expanding before the selection and one for exanding after
the selection.

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

app/ime_test.go

@@ -108,6 +108,27 @@ func FuzzIME(f *testing.F) {
 			newState := r.EditorState()
 			// We don't track caret position.
 			state.Selection.Caret = newState.Selection.Caret
+			// Expanded snippets are ok.
+			their, our := newState.Snippet, state.EditorState.Snippet
+			beforeLen := 0
+			for before := our.Start - their.Start; before > 0; before-- {
+				_, n := utf8.DecodeRuneInString(their.Text[beforeLen:])
+				beforeLen += n
+			}
+			afterLen := 0
+			for after := their.End - our.End; after > 0; after-- {
+				_, n := utf8.DecodeLastRuneInString(their.Text[:len(their.Text)-afterLen])
+				afterLen += n
+			}
+			if beforeLen > 0 {
+				our.Text = their.Text[:beforeLen] + our.Text
+				our.Start = their.Start
+			}
+			if afterLen > 0 {
+				our.Text = our.Text + their.Text[len(their.Text)-afterLen:]
+				our.End = their.End
+			}
+			state.EditorState.Snippet = our
 			if newState != state.EditorState {
 				t.Errorf("IME state: %+v\neditor state: %+v", state.EditorState, newState)
 			}

app/window.go

@@ -492,7 +492,6 @@ func (c *callbacks) EditorInsert(text string) {
 func (c *callbacks) EditorReplace(r key.Range, text string) {
 	c.w.imeState.Replace(r, text)
 	c.Event(key.EditEvent{Range: r, Text: text})
-	c.Event(key.SnippetEvent(c.w.imeState.Snippet.Range))
 }
 
 func (c *callbacks) SetEditorSelection(r key.Range) {

io/router/router.go

@@ -142,7 +142,20 @@ func (q *Router) Queue(events ...event.Event) bool {
 			q.pointer.queue.Push(e, &q.handlers)
 		case key.Event:
 			q.queueKeyEvent(e)
-		case key.EditEvent, key.FocusEvent, key.SnippetEvent, key.SelectionEvent:
+		case key.SnippetEvent:
+			// Expand existing, overlapping snippet.
+			if r := q.key.queue.content.Snippet.Range; rangeOverlaps(r, key.Range(e)) {
+				if e.Start > r.Start {
+					e.Start = r.Start
+				}
+				if e.End < r.End {
+					e.End = r.End
+				}
+			}
+			if f := q.key.queue.focus; f != nil {
+				q.handlers.Add(f, e)
+			}
+		case key.EditEvent, key.FocusEvent, key.SelectionEvent:
 			if f := q.key.queue.focus; f != nil {
 				q.handlers.Add(f, e)
 			}
@@ -153,6 +166,20 @@ func (q *Router) Queue(events ...event.Event) bool {
 	return q.handlers.HadEvents()
 }
 
+func rangeOverlaps(r1, r2 key.Range) bool {
+	r1 = rangeNorm(r1)
+	r2 = rangeNorm(r2)
+	return r1.Start <= r2.Start && r2.Start < r1.End ||
+		r1.Start <= r2.End && r2.End < r1.End
+}
+
+func rangeNorm(r key.Range) key.Range {
+	if r.End < r.Start {
+		r.End, r.Start = r.Start, r.End
+	}
+	return r
+}
+
 func (q *Router) queueKeyEvent(e key.Event) {
 	kq := &q.key.queue
 	f := q.key.queue.focus