[Layout] Treat flex factors as true factors (#2349)

* Treat flex factors as factors

* Add snapshot tests

* Address comments

AsyncDisplayKit/Private/ASStackUnpositionedLayout.mm

@@ -131,8 +131,8 @@ static const CGFloat kViolationEpsilon = 0.01;
  */
 static std::function<CGFloat(const ASStackUnpositionedItem &)> flexFactorInViolationDirection(const CGFloat violation)
 {
-  if (fabs(violation) < kViolationEpsilon) {
-    return [](const ASStackUnpositionedItem &item) { return 0; };
+  if (std::fabs(violation) < kViolationEpsilon) {
+    return [](const ASStackUnpositionedItem &item) { return 0.0; };
   } else if (violation > 0) {
     return [](const ASStackUnpositionedItem &item) { return item.child.style.flexGrow; };
   } else {
@@ -140,9 +140,11 @@ static std::function<CGFloat(const ASStackUnpositionedItem &)> flexFactorInViola
   }
 }
 
-static inline CGFloat scaledFlexShrinkFactor(const ASStackUnpositionedItem &item, const ASStackLayoutSpecStyle &style)
+static inline CGFloat scaledFlexShrinkFactor(const ASStackUnpositionedItem &item,
+                                             const ASStackLayoutSpecStyle &style,
+                                             const CGFloat flexFactorSum)
 {
-  return stackDimension(style.direction, item.layout.size) * item.child.style.flexShrink;
+  return stackDimension(style.direction, item.layout.size) * (item.child.style.flexShrink / flexFactorSum);
 }
 
 /**
@@ -150,20 +152,22 @@ static inline CGFloat scaledFlexShrinkFactor(const ASStackUnpositionedItem &item
  @param items The unpositioned items from the original unconstrained layout pass.
  @param style The layout style to be applied to all children.
  @param violation The amount that the stack layout violates its size range.
+ @param flexFactorSum The sum of each item's flex factor as determined by the provided violation.
  @return A lambda capable of computing the flex shrink adjustment, if any, for a particular item.
  */
-static std::function<CGFloat(const ASStackUnpositionedItem &, BOOL)> flexShrinkAdjustment(const std::vector<ASStackUnpositionedItem> &items,
-                                                                                          const ASStackLayoutSpecStyle &style,
-                                                                                          const CGFloat violation)
+static std::function<CGFloat(const ASStackUnpositionedItem &)> flexShrinkAdjustment(const std::vector<ASStackUnpositionedItem> &items,
+                                                                                    const ASStackLayoutSpecStyle &style,
+                                                                                    const CGFloat violation,
+                                                                                    const CGFloat flexFactorSum)
 {
-  const CGFloat scaledFlexShrinkFactorSum = std::accumulate(items.begin(), items.end(), 0, [&](CGFloat x, const ASStackUnpositionedItem &item) {
-    return x + scaledFlexShrinkFactor(item, style);
+  const CGFloat scaledFlexShrinkFactorSum = std::accumulate(items.begin(), items.end(), 0.0, [&](CGFloat x, const ASStackUnpositionedItem &item) {
+    return x + scaledFlexShrinkFactor(item, style, flexFactorSum);
   });
-  return [style, scaledFlexShrinkFactorSum, violation](const ASStackUnpositionedItem &item, BOOL isFirstFlex) {
-    const CGFloat scaledFlexShrinkFactorRatio = scaledFlexShrinkFactor(item, style) / scaledFlexShrinkFactorSum;
+  return [style, scaledFlexShrinkFactorSum, violation, flexFactorSum](const ASStackUnpositionedItem &item) {
+    const CGFloat scaledFlexShrinkFactorRatio = scaledFlexShrinkFactor(item, style, flexFactorSum) / scaledFlexShrinkFactorSum;
     // The item should shrink proportionally to the scaled flex shrink factor ratio computed above.
     // Unlike the flex grow adjustment the flex shrink adjustment needs to take the size of each item into account.
-    return -fabs(scaledFlexShrinkFactorRatio * violation);
+    return -std::fabs(scaledFlexShrinkFactorRatio * violation);
   };
 }
 
@@ -174,17 +178,13 @@ static std::function<CGFloat(const ASStackUnpositionedItem &, BOOL)> flexShrinkA
  @param flexFactorSum The sum of each item's flex factor as determined by the provided violation.
  @return A lambda capable of computing the flex grow adjustment, if any, for a particular item.
  */
-static std::function<CGFloat(const ASStackUnpositionedItem &, BOOL)> flexGrowAdjustment(const std::vector<ASStackUnpositionedItem> &items,
-                                                                                        const CGFloat violation,
-                                                                                        const CGFloat flexFactorSum)
+static std::function<CGFloat(const ASStackUnpositionedItem &)> flexGrowAdjustment(const std::vector<ASStackUnpositionedItem> &items,
+                                                                                  const CGFloat violation,
+                                                                                  const CGFloat flexFactorSum)
 {
-  const CGFloat violationPerFlexFactor = floorf(violation / flexFactorSum);
-  const CGFloat remainingViolation = violation - (violationPerFlexFactor * flexFactorSum);
   // To compute the flex grow adjustment distribute the violation proportionally based on each item's flex grow factor.
-  // If there happens to be a violation remaining make sure it is allocated to the first flexible child.
-  return [violationPerFlexFactor, remainingViolation](const ASStackUnpositionedItem &item, BOOL isFirstFlex) {
-    // Only apply the remaining violation for the first flexible child that has a flex grow factor.
-    return violationPerFlexFactor * item.child.style.flexGrow + (isFirstFlex && item.child.style.flexGrow > 0 ? remainingViolation : 0);
+  return [violation, flexFactorSum](const ASStackUnpositionedItem &item) {
+    return std::floor(violation * (item.child.style.flexGrow / flexFactorSum));
   };
 }
 
@@ -196,15 +196,15 @@ static std::function<CGFloat(const ASStackUnpositionedItem &, BOOL)> flexGrowAdj
  @param flexFactorSum The sum of each item's flex factor as determined by the provided violation.
  @return A lambda capable of computing the flex adjustment for a particular item.
  */
-static std::function<CGFloat(const ASStackUnpositionedItem &, BOOL)> flexAdjustmentInViolationDirection(const std::vector<ASStackUnpositionedItem> &items,
-                                                                                                        const ASStackLayoutSpecStyle &style,
-                                                                                                        const CGFloat violation,
-                                                                                                        const CGFloat flexFactorSum)
+static std::function<CGFloat(const ASStackUnpositionedItem &)> flexAdjustmentInViolationDirection(const std::vector<ASStackUnpositionedItem> &items,
+                                                                                                  const ASStackLayoutSpecStyle &style,
+                                                                                                  const CGFloat violation,
+                                                                                                  const CGFloat flexFactorSum)
 {
   if (violation > 0) {
     return flexGrowAdjustment(items, violation, flexFactorSum);
   } else {
-    return flexShrinkAdjustment(items, style, violation);
+    return flexShrinkAdjustment(items, style, violation, flexFactorSum);
   }
 }
 
@@ -352,7 +352,7 @@ static void flexChildrenAlongStackDimension(std::vector<ASStackUnpositionedItem>
   std::function<CGFloat(const ASStackUnpositionedItem &)> flexFactor = flexFactorInViolationDirection(violation);
   // The flex factor sum is needed to determine if flexing is necessary.
   // This value is also needed if the violation is positive and flexible children need to grow, so keep it around.
-  const CGFloat flexFactorSum = std::accumulate(items.begin(), items.end(), 0, [&](CGFloat x, const ASStackUnpositionedItem &item) {
+  const CGFloat flexFactorSum = std::accumulate(items.begin(), items.end(), 0.0, [&](CGFloat x, const ASStackUnpositionedItem &item) {
     return x + flexFactor(item);
   });
   // If no children are able to flex then there is nothing left to do. Bail.
@@ -363,17 +363,23 @@ static void flexChildrenAlongStackDimension(std::vector<ASStackUnpositionedItem>
     }
     return;
   }
-  std::function<CGFloat(const ASStackUnpositionedItem &, BOOL)> flexAdjustment = flexAdjustmentInViolationDirection(items,
-                                                                                                                    style,
-                                                                                                                    violation,
-                                                                                                                    flexFactorSum);
+  std::function<CGFloat(const ASStackUnpositionedItem &)> flexAdjustment = flexAdjustmentInViolationDirection(items,
+                                                                                                              style,
+                                                                                                              violation,
+                                                                                                              flexFactorSum);
+
+  // Compute any remaining violation to the first flexible child.
+  const CGFloat remainingViolation = std::accumulate(items.begin(), items.end(), violation, [&](CGFloat x, const ASStackUnpositionedItem &item) {
+    return x - flexAdjustment(item);
+  });
   BOOL isFirstFlex = YES;
   for (ASStackUnpositionedItem &item : items) {
-    const CGFloat currentFlexAdjustment = flexAdjustment(item, isFirstFlex);
+    const CGFloat currentFlexAdjustment = flexAdjustment(item);
     // Children are consider inflexible if they do not need to make a flex adjustment.
     if (currentFlexAdjustment != 0) {
       const CGFloat originalStackSize = stackDimension(style.direction, item.layout.size);
-      const CGFloat flexedStackSize = originalStackSize + currentFlexAdjustment;
+      // Only apply the remaining violation for the first flexible child that has a flex grow factor.
+      const CGFloat flexedStackSize = originalStackSize + currentFlexAdjustment + (isFirstFlex && item.child.style.flexGrow > 0 ? remainingViolation : 0);
       item.layout = crossChildLayout(item.child,
                                      style,
                                      MAX(flexedStackSize, 0),

AsyncDisplayKitTests/ASStackLayoutSpecSnapshotTests.mm

@@ -21,6 +21,15 @@
 
 @implementation ASStackLayoutSpecSnapshotTests
 
+#pragma mark - XCTestCase
+
+- (void)setUp
+{
+  [super setUp];
+  
+  self.recordMode = NO;
+}
+
 #pragma mark - Utility methods
 
 static NSArray<ASDisplayNode *> *defaultSubnodes()
@@ -597,13 +606,13 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testLayoutSpec:layoutSpec sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testPositiveViolationIsDistributedEquallyAmongFlexibleChildren
+- (void)testPositiveViolationIsDistributedEqually
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
   
   NSArray<ASDisplayNode *> *subnodes = defaultSubnodesWithSameSize({50, 50}, 0);
-  subnodes[0].style.flexGrow = 0;
-  subnodes[2].style.flexGrow = 0;
+  subnodes[0].style.flexGrow = 1;
+  subnodes[2].style.flexGrow = 1;
 
   // In this scenario a width of 350 results in a positive violation of 200.
   // Due to each flexible subnode specifying a flex grow factor of 1 the violation will be distributed evenly.
@@ -611,7 +620,21 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testPositiveViolationIsDistributedProportionallyAmongFlexibleChildren
+- (void)testPositiveViolationIsDistributedEquallyWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
+  
+  NSArray<ASDisplayNode *> *subnodes = defaultSubnodesWithSameSize({50, 50}, 0);
+  subnodes[0].style.flexGrow = 0.5;
+  subnodes[2].style.flexGrow = 0.5;
+  
+  // In this scenario a width of 350 results in a positive violation of 200.
+  // Due to each flexible child component specifying a flex grow factor of 0.5 the violation will be distributed evenly.
+  static ASSizeRange kSize = {{350, 350}, {350, 350}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testPositiveViolationIsDistributedProportionally
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
 
@@ -627,7 +650,23 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testPositiveViolationIsDistributedEquallyAmongGrowingAndShrinkingFlexibleChildren
+- (void)testPositiveViolationIsDistributedProportionallyWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
+
+  NSArray<ASDisplayNode *> *subnodes = defaultSubnodesWithSameSize({50, 50}, 0);
+  subnodes[0].style.flexGrow = 0.25;
+  subnodes[1].style.flexGrow = 0.50;
+  subnodes[2].style.flexGrow = 0.25;
+
+  // In this scenario a width of 350 results in a positive violation of 200.
+  // The first and third child components specify a flex grow factor of 0.25 and will flex by 50.
+  // The second child component specifies a flex grow factor of 0.25 and will flex by 100.
+  static ASSizeRange kSize = {{350, 350}, {350, 350}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testPositiveViolationIsDistributedEquallyAmongMixedChildren
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
   
@@ -647,7 +686,27 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testPositiveViolationIsDistributedProportionallyAmongGrowingAndShrinkingFlexibleChildren
+- (void)testPositiveViolationIsDistributedEquallyAmongMixedChildrenWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
+  
+  const CGSize kSubnodeSize = {50, 50};
+  NSArray<ASDisplayNode *> *subnodes = defaultSubnodesWithSameSize(kSubnodeSize, 0);
+  subnodes = [subnodes arrayByAddingObject:ASDisplayNodeWithBackgroundColor([UIColor yellowColor], kSubnodeSize)];
+  
+  subnodes[0].style.flexShrink = 1.0;
+  subnodes[1].style.flexGrow = 0.5;
+  subnodes[2].style.flexShrink = 0.0;
+  subnodes[3].style.flexGrow = 0.5;
+  
+  // In this scenario a width of 400 results in a positive violation of 200.
+  // The first and third child components specify a flex shrink factor of 1 and 0, respectively. They won't flex.
+  // The second and fourth child components specify a flex grow factor of 0.5 and will flex by 100.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testPositiveViolationIsDistributedProportionallyAmongMixedChildren
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
   
@@ -668,6 +727,27 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
+- (void)testPositiveViolationIsDistributedProportionallyAmongMixedChildrenWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
+  
+  const CGSize kSubnodeSize = {50, 50};
+  NSArray<ASDisplayNode *> *subnodes = defaultSubnodesWithSameSize(kSubnodeSize, 0);
+  subnodes = [subnodes arrayByAddingObject:ASDisplayNodeWithBackgroundColor([UIColor yellowColor], kSubnodeSize)];
+  
+  subnodes[0].style.flexShrink = 1.0;
+  subnodes[1].style.flexGrow = 0.75;
+  subnodes[2].style.flexShrink = 0.0;
+  subnodes[3].style.flexGrow = 0.25;
+  
+  // In this scenario a width of 400 results in a positive violation of 200.
+  // The first and third child components specify a flex shrink factor of 1 and 0, respectively. They won't flex.
+  // The second child component specifies a flex grow factor of 0.75 and will flex by 150.
+  // The fourth child component specifies a flex grow factor of 0.25 and will flex by 50.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
 - (void)testRemainingViolationIsAppliedProperlyToFirstFlexibleChild
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
@@ -688,7 +768,27 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testNegativeViolationIsDistributedProportionallyBasedOnSizeAmongFlexibleChildren
+- (void)testRemainingViolationIsAppliedProperlyToFirstFlexibleChildWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
+  
+  NSArray<ASDisplayNode *> *subnodes = @[
+    ASDisplayNodeWithBackgroundColor([UIColor greenColor], {50, 25}),
+    ASDisplayNodeWithBackgroundColor([UIColor blueColor], {50, 0}),
+    ASDisplayNodeWithBackgroundColor([UIColor redColor], {50, 100})
+  ];
+
+  subnodes[0].style.flexGrow = 0.0;
+  subnodes[1].style.flexGrow = 0.5;
+  subnodes[2].style.flexGrow = 0.5;
+  
+  // In this scenario a width of 300 results in a positive violation of 175.
+  // The second and third child components specify a flex grow factor of 0.5 and will flex by 88 and 87, respectively.
+  static ASSizeRange kSize = {{300, 300}, {300, 300}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testNegativeViolationIsDistributedBasedOnSize
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
   
@@ -708,7 +808,27 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testNegativeViolationIsDistributedProportionallyBasedOnSizeAndFlexFactorAmongFlexibleChildren
+- (void)testNegativeViolationIsDistributedBasedOnSizeWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
+  
+  NSArray<ASDisplayNode *> *subnodes = @[
+    ASDisplayNodeWithBackgroundColor([UIColor greenColor], {300, 50}),
+    ASDisplayNodeWithBackgroundColor([UIColor blueColor], {100, 50}),
+    ASDisplayNodeWithBackgroundColor([UIColor redColor], {200, 50})
+  ];
+  
+  subnodes[0].style.flexShrink = 0.5;
+  subnodes[1].style.flexShrink = 0.0;
+  subnodes[2].style.flexShrink = 0.5;
+
+  // In this scenario a width of 400 results in a negative violation of 200.
+  // The first and third child components specify a flex shrink factor of 0.5 and will flex by -120 and -80, respectively.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testNegativeViolationIsDistributedBasedOnSizeAndFlexFactor
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
   
@@ -729,7 +849,28 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testNegativeViolationIsDistributedProportionallyBasedOnSizeAmongGrowingAndShrinkingFlexibleChildren
+- (void)testNegativeViolationIsDistributedBasedOnSizeAndFlexFactorWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
+  
+  NSArray<ASDisplayNode *> *subnodes = @[
+    ASDisplayNodeWithBackgroundColor([UIColor greenColor], {50, 300}),
+    ASDisplayNodeWithBackgroundColor([UIColor blueColor], {50, 100}),
+    ASDisplayNodeWithBackgroundColor([UIColor redColor], {50, 200})
+  ];
+  
+  subnodes[0].style.flexShrink = 0.4;
+  subnodes[1].style.flexShrink = 0.2;
+  subnodes[2].style.flexShrink = 0.4;
+
+  // In this scenario a width of 400 results in a negative violation of 200.
+  // The first and third child components specify a flex shrink factor of 0.4 and will flex by -109 and -72, respectively.
+  // The second child component specifies a flex shrink factor of 0.2 and will flex by -18.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testNegativeViolationIsDistributedBasedOnSizeAmongMixedChildrenChildren
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
   
@@ -749,7 +890,27 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testNegativeViolationIsDistributedProportionallyBasedOnSizeAndFlexFactorAmongGrowingAndShrinkingFlexibleChildren
+- (void)testNegativeViolationIsDistributedBasedOnSizeAmongMixedChildrenWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
+  
+  const CGSize kSubnodeSize = {150, 50};
+  NSArray<ASDisplayNode *> *subnodes = defaultSubnodesWithSameSize(kSubnodeSize, 0);
+  subnodes = [subnodes arrayByAddingObject:ASDisplayNodeWithBackgroundColor([UIColor yellowColor], kSubnodeSize)];
+  
+  subnodes[0].style.flexGrow = 1.0;
+  subnodes[1].style.flexShrink = 0.5;
+  subnodes[2].style.flexGrow = 0.0;
+  subnodes[3].style.flexShrink = 0.5;
+  
+  // In this scenario a width of 400 results in a negative violation of 200.
+  // The first and third child components specify a flex grow factor of 1 and 0, respectively. They won't flex.
+  // The second and fourth child components specify a flex shrink factor of 0.5 and will flex by -100.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testNegativeViolationIsDistributedBasedOnSizeAndFlexFactorAmongMixedChildren
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
   
@@ -773,7 +934,31 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
-- (void)testNegativeViolationIsDistributedProportionallyBasedOnSizeAndFlexFactorDoesNotShrinkToZeroWidth
+- (void)testNegativeViolationIsDistributedBasedOnSizeAndFlexFactorAmongMixedChildrenArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionVertical};
+  
+  NSArray<ASDisplayNode *> *subnodes = @[
+    ASDisplayNodeWithBackgroundColor([UIColor greenColor], {50, 150}),
+    ASDisplayNodeWithBackgroundColor([UIColor blueColor], {50, 100}),
+    ASDisplayNodeWithBackgroundColor([UIColor redColor], {50, 150}),
+    ASDisplayNodeWithBackgroundColor([UIColor yellowColor], {50, 200})
+  ];
+  
+  subnodes[0].style.flexGrow = 1.0;
+  subnodes[1].style.flexShrink = 0.25;
+  subnodes[2].style.flexGrow = 0.0;
+  subnodes[3].style.flexShrink = 0.75;
+  
+  // In this scenario a width of 400 results in a negative violation of 200.
+  // The first and third child components specify a flex grow factor of 1 and 0, respectively. They won't flex.
+  // The second child component specifies a flex shrink factor of 0.25 and will flex by -28.
+  // The fourth child component specifies a flex shrink factor of 0.75 and will flex by -171.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
+- (void)testNegativeViolationIsDistributedBasedOnSizeAndFlexFactorDoesNotShrinkToZero
 {
   ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
   
@@ -794,6 +979,27 @@ static void setCGSizeToNode(CGSize size, ASDisplayNode *node)
   [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
 }
 
+- (void)testNegativeViolationIsDistributedBasedOnSizeAndFlexFactorDoesNotShrinkToZeroWithArbitraryFloats
+{
+  ASStackLayoutSpecStyle style = {.direction = ASStackLayoutDirectionHorizontal};
+  
+  NSArray<ASDisplayNode *> *subnodes = @[
+    ASDisplayNodeWithBackgroundColor([UIColor greenColor], {300, 50}),
+    ASDisplayNodeWithBackgroundColor([UIColor blueColor], {100, 50}),
+    ASDisplayNodeWithBackgroundColor([UIColor redColor], {200, 50})
+  ];
+  
+  subnodes[0].style.flexShrink = 0.25;
+  subnodes[1].style.flexShrink = 0.50;
+  subnodes[2].style.flexShrink = 0.25;
+  
+  // In this scenario a width of 400 results in a negative violation of 200.
+  // The first and third child components specify a flex shrink factor of 0.25 and will flex by 50.
+  // The second child component specifies a flex shrink factor of 0.50 and will flex by -57. It will have a width of 43.
+  static ASSizeRange kSize = {{400, 400}, {400, 400}};
+  [self testStackLayoutSpecWithStyle:style sizeRange:kSize subnodes:subnodes identifier:nil];
+}
+
 - (void)testNestedStackLayoutStretchDoesNotViolateWidth
 {
   ASStackLayoutSpec *stackLayoutSpec = [[ASStackLayoutSpec alloc] init]; // Default direction is horizontal