Do not notify text watchers when replace is a no-op

Bug 6344997

The early exit we used to do when both replaced and replacement
strings were empty has been added back.

Only this time it correctly also makes sure no spans from the
replacement string would get added with a 0-length.

Change-Id: Ifc38a7e3619c57aa7647c0a8e63d7627d86f1036

Author: Gilles Debunne

core/java/android/text/SpannableStringBuilder.java

@@ -428,6 +428,12 @@ public SpannableStringBuilder replace(final int start, final int end,
         final int origLen = end - start;
         final int newLen = tbend - tbstart;
 
+        if (origLen == 0 && newLen == 0 && !hasNonExclusiveExclusiveSpanAt(tb, tbstart)) {
+            // This is a no-op iif there are no spans in tb that would be added (with a 0-length)
+            // Early exit so that the text watchers do not get notified
+            return this;
+        }
+
         TextWatcher[] textWatchers = getSpans(start, start + origLen, TextWatcher.class);
         sendBeforeTextChanged(textWatchers, start, origLen, newLen);
 
@@ -470,6 +476,20 @@ public SpannableStringBuilder replace(final int start, final int end,
         return this; 
     }
 
+    private static boolean hasNonExclusiveExclusiveSpanAt(CharSequence text, int offset) {
+        if (text instanceof Spanned) {
+            Spanned spanned = (Spanned) text;
+            Object[] spans = spanned.getSpans(offset, offset, Object.class);
+            final int length = spans.length;
+            for (int i = 0; i < length; i++) {
+                Object span = spans[i];
+                int flags = spanned.getSpanFlags(span);
+                if (flags != Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) return true;
+            }
+        }
+        return false;
+    }
+
     private void sendToSpanWatchers(int replaceStart, int replaceEnd, int nbNewChars) {
         for (int i = 0; i < mSpanCountBeforeAdd; i++) {
             int spanStart = mSpanStarts[i];