[ASTextNode] Fix text node truncation (#1863)

* Before truncate a text storage in ASTextKitContext reset the text storage to original value

* Fix ASTextNode tests

We should pass in the constrained size in both cases and the sizes should be the same. We adjust the calculated size in ASTextNode to be a bit narrower in the second case if we truncate again with the calculated size as constrained size it will truncate more and the resulting size will shrink.

AsyncDisplayKit/TextKit/ASTextKitContext.h

@@ -10,6 +10,8 @@
 
 #import <UIKit/UIKit.h>
 
+typedef NSTextStorage *(^ASTextKitContextTextStorageCreationBlock)(NSAttributedString *attributedString);
+
 /**
  A threadsafe container for the TextKit components that ASTextKit uses to lay out and truncate its text.
 
@@ -30,10 +32,19 @@
                          constrainedSize:(CGSize)constrainedSize
               layoutManagerCreationBlock:(NSLayoutManager * (^)(void))layoutCreationBlock
                    layoutManagerDelegate:(id<NSLayoutManagerDelegate>)layoutManagerDelegate
-                textStorageCreationBlock:(NSTextStorage * (^)(NSAttributedString *attributedString))textStorageCreationBlock;
+                textStorageCreationBlock:(ASTextKitContextTextStorageCreationBlock)textStorageCreationBlock;
 
+/**
+ Set the constrained size for the text context.
+ */
 @property (nonatomic, assign, readwrite) CGSize constrainedSize;
 
+/**
+ Resets the text storage to the original value in case it was truncated before. This method is called within
+ a locked context.
+ */
+- (void)resetTextStorage;
+
 /**
  All operations on TextKit values MUST occur within this locked context.  Simultaneous access (even non-mutative) to
  TextKit components may cause crashes.

AsyncDisplayKit/TextKit/ASTextKitContext.mm

@@ -21,8 +21,12 @@
   NSLayoutManager *_layoutManager;
   NSTextStorage *_textStorage;
   NSTextContainer *_textContainer;
+  
+  NSAttributedString *_attributedString;
 }
 
+#pragma mark - Lifecycle
+
 - (instancetype)initWithAttributedString:(NSAttributedString *)attributedString
                            lineBreakMode:(NSLineBreakMode)lineBreakMode
                     maximumNumberOfLines:(NSUInteger)maximumNumberOfLines
@@ -37,16 +41,23 @@
     // Concurrently initialising TextKit components crashes (rdar://18448377) so we use a global lock.
     static std::mutex __static_mutex;
     std::lock_guard<std::mutex> l(__static_mutex);
+    
+    _attributedString = [attributedString copy];
+    
     // Create the TextKit component stack with our default configuration.
     if (textStorageCreationBlock) {
       _textStorage = textStorageCreationBlock(attributedString);
     } else {
-      _textStorage = (attributedString ? [[NSTextStorage alloc] initWithAttributedString:attributedString] : [[NSTextStorage alloc] init]);
+      _textStorage = [[NSTextStorage alloc] init];
+      [self _resetTextStorage];
     }
+    
+    
     _layoutManager = layoutCreationBlock ? layoutCreationBlock() : [[ASLayoutManager alloc] init];
     _layoutManager.usesFontLeading = NO;
     _layoutManager.delegate = layoutManagerDelegate;
     [_textStorage addLayoutManager:_layoutManager];
+
     _textContainer = [[NSTextContainer alloc] initWithSize:constrainedSize];
     // We want the text laid out up to the very edges of the container.
     _textContainer.lineFragmentPadding = 0;
@@ -58,6 +69,21 @@
   return self;
 }
 
+#pragma mark - Text Storage
+
+- (void)resetTextStorage
+{
+  std::lock_guard<std::mutex> l(_textKitMutex);
+  [self _resetTextStorage];
+}
+
+- (void)_resetTextStorage
+{
+  [_textStorage setAttributedString:_attributedString];
+}
+
+#pragma mark - Setter / Getter
+
 - (CGSize)constrainedSize
 {
   std::lock_guard<std::mutex> l(_textKitMutex);
@@ -70,6 +96,8 @@
   _textContainer.size = constrainedSize;
 }
 
+#pragma mark - Locking
+
 - (void)performBlockWithLockedTextKitComponents:(void (^)(NSLayoutManager *,
                                                           NSTextStorage *,
                                                           NSTextContainer *))block

AsyncDisplayKit/TextKit/ASTextKitRenderer.mm

@@ -129,8 +129,12 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
       // If we're updating an existing context, make sure to use the same inset logic used during initialization.
       // This codepath allows us to reuse the
       CGSize shadowConstrainedSize = [[self shadower] insetSizeWithConstrainedSize:constrainedSize];
-      if (_context) _context.constrainedSize = shadowConstrainedSize;
-      if (_fontSizeAdjuster) _fontSizeAdjuster.constrainedSize = shadowConstrainedSize;
+      if (_context) {
+        _context.constrainedSize = shadowConstrainedSize;
+      }
+      if (_fontSizeAdjuster) {
+        _fontSizeAdjuster.constrainedSize = shadowConstrainedSize;
+      }
     }
   }
 }

AsyncDisplayKit/TextKit/ASTextKitTailTruncater.mm

@@ -152,7 +152,12 @@
 
 - (void)truncate
 {
+  // Reset the text storage to start always with the full string
+  [_context resetTextStorage];
+
+  // Start truncation
   [_context performBlockWithLockedTextKitComponents:^(NSLayoutManager *layoutManager, NSTextStorage *textStorage, NSTextContainer *textContainer) {
+    
     NSUInteger originalStringLength = textStorage.length;
     
     [layoutManager ensureLayoutForTextContainer:textContainer];

AsyncDisplayKitTests/ASTextNodeTests.m

@@ -125,7 +125,7 @@ static BOOL CGSizeEqualToSizeWithIn(CGSize size1, CGSize size2, CGFloat delta)
   for (NSInteger i = 10; i < 500; i += 50) {
     CGSize constrainedSize = CGSizeMake(i, i);
     CGSize calculatedSize = [_textNode measure:constrainedSize];
-    CGSize recalculatedSize = [_textNode measure:calculatedSize];
+    CGSize recalculatedSize = [_textNode measure:constrainedSize];
     
     XCTAssertTrue(CGSizeEqualToSizeWithIn(calculatedSize, recalculatedSize, 4.0), @"Recalculated size %@ should be same as original size %@", NSStringFromCGSize(recalculatedSize), NSStringFromCGSize(calculatedSize));
   }
@@ -136,7 +136,7 @@ static BOOL CGSizeEqualToSizeWithIn(CGSize size1, CGSize size2, CGFloat delta)
   for (CGFloat i = 10; i < 500; i *= 1.3) {
     CGSize constrainedSize = CGSizeMake(i, i);
     CGSize calculatedSize = [_textNode measure:constrainedSize];
-    CGSize recalculatedSize = [_textNode measure:calculatedSize];
+    CGSize recalculatedSize = [_textNode measure:constrainedSize];
 
     XCTAssertTrue(CGSizeEqualToSizeWithIn(calculatedSize, recalculatedSize, 11.0), @"Recalculated size %@ should be same as original size %@", NSStringFromCGSize(recalculatedSize), NSStringFromCGSize(calculatedSize));
   }