Small changes required by the coming layout debugger (#337)

* Small changes required by the layout debugger
- `ASDisplayNode` can be told to not flatten its layout immediately but later on. The unflattened layout is also stored in a separate property. It's needed for inspecting not only display nodes but also layout specs used to compute a layout tree.
- `ASLayout` can be told to always retain its sublayout elements. This is needed especially for layout specs since they are usually not retained after an ASLayout was computed.

* Update CHANGELOG

* Address comments

CHANGELOG.md

@@ -34,4 +34,5 @@
 - [Fix] Fix a major regression in our image node contents caching. [Adlai Holler](https://github.com/Adlai-Holler) [#287](https://github.com/TextureGroup/Texture/pull/287)
 - [Fix] Fixed a bug where ASVideoNodeDelegate error reporting callback would crash an app because of not responding to selector. [Sergey Petrachkov](https://github.com/Petrachkov) [#291](https://github.com/TextureGroup/Texture/issues/291)
 - [IGListKit] Add IGListKit headers to public section of Xcode project [Michael Schneider](https://github.com/maicki)[#286](https://github.com/TextureGroup/Texture/pull/286)
-- [Layout] Ensure -layout and -layoutDidFinish are called only if a node is loaded. [Huy Nguyen](https://github.com/nguyenhuy) [#285](https://github.com/TextureGroup/Texture/pull/285)
+- [Layout] Ensure -layout and -layoutDidFinish are called only if a node is loaded. [Huy Nguyen](https://github.com/nguyenhuy) [#285](https://github.com/TextureGroup/Texture/pull/285)
+- [Layout Debugger] Small changes needed for the coming layout debugger [Huy Nguyen](https://github.com/nguyenhuy) [#337](https://github.com/TextureGroup/Texture/pull/337)

Source/ASDisplayNode+Layout.mm

@@ -911,6 +911,12 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
   ASDisplayNodeAssertTrue(displayNodeLayout->layout.size.width >= 0.0);
   ASDisplayNodeAssertTrue(displayNodeLayout->layout.size.height >= 0.0);
   
+  // Flatten the layout if it wasn't done before (@see -calculateLayoutThatFits:).
+  if ([ASDisplayNode shouldStoreUnflattenedLayouts]) {
+    _unflattenedLayout = displayNodeLayout->layout;
+    displayNodeLayout->layout = [_unflattenedLayout filteredNodeLayoutTree];
+  }
+  
   _calculatedDisplayNodeLayout = displayNodeLayout;
 }
 

Source/ASDisplayNode.h

@@ -553,6 +553,30 @@ extern NSInteger const ASDefaultDrawingPriority;
  */
 @interface ASDisplayNode (Debugging) <ASDebugNameProvider>
 
+/**
+ * Set to YES to tell all ASDisplayNode instances to store their unflattened layouts.
+ *
+ * The layout can be accessed via `-unflattenedCalculatedLayout`.
+ *
+ * Flattened layouts use less memory and are faster to lookup. On the other hand, unflattened layouts are useful for debugging
+ * because they preserve original information.
+ */
++ (void)setShouldStoreUnflattenedLayouts:(BOOL)shouldStore;
+
+/**
+ * Whether or not ASDisplayNode instances should store their unflattened layouts. 
+ *
+ * The layout can be accessed via `-unflattenedCalculatedLayout`.
+ * 
+ * Flattened layouts use less memory and are faster to lookup. On the other hand, unflattened layouts are useful for debugging
+ * because they preserve original information.
+ *
+ * Defaults to NO.
+ */
++ (BOOL)shouldStoreUnflattenedLayouts;
+
+@property (nonatomic, strong, readonly, nullable) ASLayout *unflattenedCalculatedLayout;
+
 /**
  * @abstract Return a description of the node hierarchy.
  *

Source/ASDisplayNode.mm

@@ -82,6 +82,7 @@ NSInteger const ASDefaultDrawingPriority = ASDefaultTransactionPriority;
 @synthesize threadSafeBounds = _threadSafeBounds;
 
 static BOOL suppressesInvalidCollectionUpdateExceptions = NO;
+static std::atomic_bool storesUnflattenedLayouts = ATOMIC_VAR_INIT(NO);
 
 + (BOOL)suppressesInvalidCollectionUpdateExceptions
 {
@@ -887,6 +888,8 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   if (_pendingDisplayNodeLayout != nullptr) {
     _pendingDisplayNodeLayout->invalidate();
   }
+  
+  _unflattenedLayout = nil;
 
 #if YOGA_TREE_CONTIGUOUS
   [self invalidateCalculatedYogaLayout];
@@ -1013,7 +1016,6 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   
   // Manually propagate the trait collection here so that any layoutSpec children of layoutSpec will get a traitCollection
   {
-    
     ASDN::SumScopeTimer t(_layoutSpecTotalTime, measureLayoutSpec);
     ASTraitCollectionPropagateDown(layoutElement, self.primitiveTraitCollection);
   }
@@ -1038,7 +1040,13 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   }
   ASDisplayNodeLogEvent(self, @"computedLayout: %@", layout);
 
-  return [layout filteredNodeLayoutTree];
+  // Return the (original) unflattened layout if it needs to be stored. The layout will be flattened later on (@see _locked_setCalculatedDisplayNodeLayout:).
+  // Otherwise, flatten it right away.
+  if (! [ASDisplayNode shouldStoreUnflattenedLayouts]) {
+    layout = [layout filteredNodeLayoutTree];
+  }
+  
+  return layout;
 }
 
 - (CGSize)calculateSizeThatFits:(CGSize)constrainedSize
@@ -3286,6 +3294,22 @@ ASDISPLAYNODE_INLINE BOOL subtreeIsRasterized(ASDisplayNode *node) {
 
 @implementation ASDisplayNode (Debugging)
 
++ (void)setShouldStoreUnflattenedLayouts:(BOOL)shouldStore
+{
+  storesUnflattenedLayouts.store(shouldStore);
+}
+
++ (BOOL)shouldStoreUnflattenedLayouts
+{
+  return storesUnflattenedLayouts.load();
+}
+
+- (ASLayout *)unflattenedCalculatedLayout
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  return _unflattenedLayout;
+}
+
 - (NSString *)displayNodeRecursiveDescription
 {
   return [self _recursiveDescriptionHelperWithIndent:@""];

Source/ASDisplayNodeExtras.h

@@ -98,7 +98,7 @@ extern ASDisplayNode * _Nullable ASLayerToDisplayNode(CALayer * _Nullable layer)
 extern ASDisplayNode * _Nullable ASViewToDisplayNode(UIView * _Nullable view) AS_WARN_UNUSED_RESULT;
 
 /**
- Given a node, returns the root of the node heirarchy (where supernode == nil)
+ Given a node, returns the root of the node hierarchy (where supernode == nil)
  */
 extern ASDisplayNode *ASDisplayNodeUltimateParentOfNode(ASDisplayNode *node) AS_WARN_UNUSED_RESULT;
 

Source/Layout/ASLayout.h

@@ -176,6 +176,18 @@ ASDISPLAYNODE_EXTERN_C_END
 
 @interface ASLayout (Debugging)
 
+/**
+ * Set to YES to tell all ASLayout instances to retain their sublayout elements. Defaults to NO.
+ * Can be overridden at instance level.
+ */
++ (void)setShouldRetainSublayoutLayoutElements:(BOOL)shouldRetain;
+
+/**
+ * Whether or not ASLayout instances should retain their sublayout elements.
+ * Can be overridden at instance level.
+ */
++ (BOOL)shouldRetainSublayoutLayoutElements;
+
 /**
  * Recrusively output the description of the layout tree.
  */

Source/Layout/ASLayout.mm

@@ -76,6 +76,18 @@ static inline NSString * descriptionIndents(NSUInteger indents)
 
 @dynamic frame, type;
 
+static std::atomic_bool static_retainsSublayoutLayoutElements = ATOMIC_VAR_INIT(NO);
+
++ (void)setShouldRetainSublayoutLayoutElements:(BOOL)shouldRetain
+{
+  static_retainsSublayoutLayoutElements.store(shouldRetain);
+}
+
++ (BOOL)shouldRetainSublayoutLayoutElements
+{
+  return static_retainsSublayoutLayoutElements.load();
+}
+
 - (instancetype)initWithLayoutElement:(id<ASLayoutElement>)layoutElement
                                  size:(CGSize)size
                              position:(CGPoint)position
@@ -118,7 +130,7 @@ static inline NSString * descriptionIndents(NSUInteger indents)
     }
     
     _flattened = NO;
-    _retainSublayoutLayoutElements = NO;
+    self.retainSublayoutLayoutElements = [ASLayout shouldRetainSublayoutLayoutElements];
   }
   
   return self;

Source/Private/ASDisplayNodeInternal.h

@@ -211,6 +211,9 @@ FOUNDATION_EXPORT NSString * const ASRenderingEngineDidDisplayNodesScheduledBefo
   
   NSString *_debugName;
 
+#pragma mark - ASDisplayNode (Debugging)
+  ASLayout *_unflattenedLayout;
+
 #if TIME_DISPLAYNODE_OPS
 @public
   NSTimeInterval _debugTimeToCreateView;