[ASTextNode] Ensure that isTruncated computes the correct value when sizing fast-path is used. (#2550) (#2763)

* Fix fast-path isTruncated.

* Clean up formatting; remove extra char.

AsyncDisplayKit/ASTextNode.mm

@@ -1163,7 +1163,7 @@ static NSAttributedString *DefaultTruncationAttributedString()
   ASDN::MutexLocker l(__instanceLock__);
   
   ASTextKitRenderer *renderer = [self _renderer];
-  return renderer.firstVisibleRange.length < _attributedText.length;
+  return renderer.isTruncated;
 }
 
 - (void)setPointSizeScaleFactors:(NSArray *)pointSizeScaleFactors

AsyncDisplayKit/TextKit/ASTextKitRenderer.h

@@ -85,6 +85,11 @@
  */
 - (NSUInteger)lineCount;
 
+/**
+ Whether or not the text is truncated.
+ */
+- (BOOL)isTruncated;
+
 @end
 
 @interface ASTextKitRenderer (ASTextKitRendererConvenience)

AsyncDisplayKit/TextKit/ASTextKitRenderer.mm

@@ -261,6 +261,18 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
   return lineCount;
 }
 
+- (BOOL)isTruncated
+{
+  if (self.canUseFastPath) {
+    CGRect boundedRect = [_attributes.attributedString boundingRectWithSize:CGSizeMake(_constrainedSize.width, CGFLOAT_MAX)
+                                                                    options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingTruncatesLastVisibleLine
+                                                                    context:nil];
+    return boundedRect.size.height > _constrainedSize.height;
+  } else {
+    return self.firstVisibleRange.length < _attributes.attributedString.length;
+  }
+}
+
 - (std::vector<NSRange>)visibleRanges
 {
   return _truncater.visibleRanges;