Use CSS terminology for sizing rules (#1460)

Summary:
X-link: https://github.com/facebook/react-native/pull/41390

Pull Request resolved: https://github.com/facebook/yoga/pull/1460

Yoga passes `MeasureMode`/`YGMeasureMode` to express constraints in how a box should be measured, given definite or indefinite available space.

This is modeled after Android [MeasureSpec](https://developer.android.com/reference/android/view/View.MeasureSpec), with a table above `calculateLayoutImpl()` explaining the CSS terms they map to. This can be confusing when flipping between the spec, and code.

This switches internal usages to the CSS terms, but leaves around `YGMeasureMode` since it is the public API passed to measure functions.

Reviewed By: joevilches

Differential Revision: D51068417

fbshipit-source-id: 0a76266a4e7e0cc39996164607229c3c41de2818

yoga/YGNode.cpp

@@ -351,13 +351,13 @@ bool YGNodeCanUseCachedMeasurement(
     float marginColumn,
     YGConfigRef config) {
   return yoga::canUseCachedMeasurement(
-      scopedEnum(widthMode),
+      sizingMode(scopedEnum(widthMode)),
       availableWidth,
-      scopedEnum(heightMode),
+      sizingMode(scopedEnum(heightMode)),
       availableHeight,
-      scopedEnum(lastWidthMode),
+      sizingMode(scopedEnum(lastWidthMode)),
       lastAvailableWidth,
-      scopedEnum(lastHeightMode),
+      sizingMode(scopedEnum(lastHeightMode)),
       lastAvailableHeight,
       lastComputedWidth,
       lastComputedHeight,

yoga/YGNode.h

@@ -186,6 +186,19 @@ typedef struct YGSize {
 } YGSize;
 
 /**
+ * Returns the computed dimensions of the node, following the contraints of
+ * `widthMode` and `heightMode`:
+ *
+ * YGMeasureModeUndefined: The parent has not imposed any constraint on the
+ * child. It can be whatever size it wants.
+ *
+ * YGMeasureModeAtMost: The child can be as large as it wants up to the
+ * specified size.
+ *
+ * YGMeasureModeExactly: The parent has determined an exact size for the
+ * child. The child is going to be given those bounds regardless of how big it
+ * wants to be.
+ *
  * @returns the size of the leaf node, measured under the given contraints.
  */
 typedef YGSize (*YGMeasureFunc)(

yoga/algorithm/Cache.cpp

@@ -12,51 +12,52 @@
 namespace facebook::yoga {
 
 static inline bool sizeIsExactAndMatchesOldMeasuredSize(
-    MeasureMode sizeMode,
+    SizingMode sizeMode,
     float size,
     float lastComputedSize) {
-  return sizeMode == MeasureMode::Exactly &&
+  return sizeMode == SizingMode::StretchFit &&
       yoga::inexactEquals(size, lastComputedSize);
 }
 
-static inline bool oldSizeIsUnspecifiedAndStillFits(
-    MeasureMode sizeMode,
+static inline bool oldSizeIsMaxContentAndStillFits(
+    SizingMode sizeMode,
     float size,
-    MeasureMode lastSizeMode,
+    SizingMode lastSizeMode,
     float lastComputedSize) {
-  return sizeMode == MeasureMode::AtMost &&
-      lastSizeMode == MeasureMode::Undefined &&
+  return sizeMode == SizingMode::FitContent &&
+      lastSizeMode == SizingMode::MaxContent &&
       (size >= lastComputedSize || yoga::inexactEquals(size, lastComputedSize));
 }
 
-static inline bool newMeasureSizeIsStricterAndStillValid(
-    MeasureMode sizeMode,
+static inline bool newSizeIsStricterAndStillValid(
+    SizingMode sizeMode,
     float size,
-    MeasureMode lastSizeMode,
+    SizingMode lastSizeMode,
     float lastSize,
     float lastComputedSize) {
-  return lastSizeMode == MeasureMode::AtMost &&
-      sizeMode == MeasureMode::AtMost && !std::isnan(lastSize) &&
-      !std::isnan(size) && !std::isnan(lastComputedSize) && lastSize > size &&
+  return lastSizeMode == SizingMode::FitContent &&
+      sizeMode == SizingMode::FitContent && yoga::isDefined(lastSize) &&
+      yoga::isDefined(size) && yoga::isDefined(lastComputedSize) &&
+      lastSize > size &&
       (lastComputedSize <= size || yoga::inexactEquals(size, lastComputedSize));
 }
 
 bool canUseCachedMeasurement(
-    const MeasureMode widthMode,
+    const SizingMode widthMode,
     const float availableWidth,
-    const MeasureMode heightMode,
+    const SizingMode heightMode,
     const float availableHeight,
-    const MeasureMode lastWidthMode,
+    const SizingMode lastWidthMode,
     const float lastAvailableWidth,
-    const MeasureMode lastHeightMode,
+    const SizingMode lastHeightMode,
     const float lastAvailableHeight,
     const float lastComputedWidth,
     const float lastComputedHeight,
     const float marginRow,
     const float marginColumn,
     const yoga::Config* const config) {
-  if ((!std::isnan(lastComputedHeight) && lastComputedHeight < 0) ||
-      (!std::isnan(lastComputedWidth) && lastComputedWidth < 0)) {
+  if ((yoga::isDefined(lastComputedHeight) && lastComputedHeight < 0) ||
+      ((yoga::isDefined(lastComputedWidth)) && lastComputedWidth < 0)) {
     return false;
   }
 
@@ -87,33 +88,32 @@ bool canUseCachedMeasurement(
       hasSameWidthSpec ||
       sizeIsExactAndMatchesOldMeasuredSize(
           widthMode, availableWidth - marginRow, lastComputedWidth) ||
-      oldSizeIsUnspecifiedAndStillFits(
+      oldSizeIsMaxContentAndStillFits(
           widthMode,
           availableWidth - marginRow,
           lastWidthMode,
           lastComputedWidth) ||
-      newMeasureSizeIsStricterAndStillValid(
+      newSizeIsStricterAndStillValid(
           widthMode,
           availableWidth - marginRow,
           lastWidthMode,
           lastAvailableWidth,
           lastComputedWidth);
 
-  const bool heightIsCompatible =
-      hasSameHeightSpec ||
+  const bool heightIsCompatible = hasSameHeightSpec ||
       sizeIsExactAndMatchesOldMeasuredSize(
-          heightMode, availableHeight - marginColumn, lastComputedHeight) ||
-      oldSizeIsUnspecifiedAndStillFits(
-          heightMode,
-          availableHeight - marginColumn,
-          lastHeightMode,
-          lastComputedHeight) ||
-      newMeasureSizeIsStricterAndStillValid(
-          heightMode,
-          availableHeight - marginColumn,
-          lastHeightMode,
-          lastAvailableHeight,
-          lastComputedHeight);
+                                      heightMode,
+                                      availableHeight - marginColumn,
+                                      lastComputedHeight) ||
+      oldSizeIsMaxContentAndStillFits(heightMode,
+                                      availableHeight - marginColumn,
+                                      lastHeightMode,
+                                      lastComputedHeight) ||
+      newSizeIsStricterAndStillValid(heightMode,
+                                     availableHeight - marginColumn,
+                                     lastHeightMode,
+                                     lastAvailableHeight,
+                                     lastComputedHeight);
 
   return widthIsCompatible && heightIsCompatible;
 }

yoga/algorithm/Cache.h

@@ -7,19 +7,19 @@
 
 #pragma once
 
+#include <yoga/algorithm/SizingMode.h>
 #include <yoga/config/Config.h>
-#include <yoga/enums/MeasureMode.h>
 
 namespace facebook::yoga {
 
 bool canUseCachedMeasurement(
-    MeasureMode widthMode,
+    SizingMode widthMode,
     float availableWidth,
-    MeasureMode heightMode,
+    SizingMode heightMode,
     float availableHeight,
-    MeasureMode lastWidthMode,
+    SizingMode lastWidthMode,
     float lastAvailableWidth,
-    MeasureMode lastHeightMode,
+    SizingMode lastHeightMode,
     float lastAvailableHeight,
     float lastComputedWidth,
     float lastComputedHeight,

yoga/algorithm/SizingMode.h

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <yoga/debug/AssertFatal.h>
+#include <yoga/enums/MeasureMode.h>
+
+namespace facebook::yoga {
+
+/**
+ * Corresponds to a CSS auto box sizes. Missing "min-content", as Yoga does not
+ * current support automatic minimum sizes.
+ * https://www.w3.org/TR/css-sizing-3/#auto-box-sizes
+ * https://www.w3.org/TR/css-flexbox-1/#min-size-auto
+ */
+enum class SizingMode {
+  /**
+   * The size a box would take if its outer size filled the available space in
+   * the given axis; in other words, the stretch fit into the available space,
+   * if that is definite. Undefined if the available space is indefinite.
+   */
+  StretchFit,
+
+  /**
+   * A box’s “ideal” size in a given axis when given infinite available space.
+   * Usually this is the smallest size the box could take in that axis while
+   * still fitting around its contents, i.e. minimizing unfilled space while
+   * avoiding overflow.
+   */
+  MaxContent,
+
+  /**
+   * If the available space in a given axis is definite, equal to
+   * clamp(min-content size, stretch-fit size, max-content size) (i.e.
+   * max(min-content size, min(max-content size, stretch-fit size))). When
+   * sizing under a min-content constraint, equal to the min-content size.
+   * Otherwise, equal to the max-content size in that axis.
+   */
+  FitContent,
+};
+
+inline MeasureMode measureMode(SizingMode mode) {
+  switch (mode) {
+    case SizingMode::StretchFit:
+      return MeasureMode::Exactly;
+    case SizingMode::MaxContent:
+      return MeasureMode::Undefined;
+    case SizingMode::FitContent:
+      return MeasureMode::AtMost;
+  }
+
+  fatalWithMessage("Invalid SizingMode");
+}
+
+inline SizingMode sizingMode(MeasureMode mode) {
+  switch (mode) {
+    case MeasureMode::Exactly:
+      return SizingMode::StretchFit;
+    case MeasureMode::Undefined:
+      return SizingMode::MaxContent;
+    case MeasureMode::AtMost:
+      return SizingMode::FitContent;
+  }
+
+  fatalWithMessage("Invalid MeasureMode");
+}
+
+} // namespace facebook::yoga

yoga/debug/AssertFatal.cpp

@@ -7,8 +7,10 @@
 
 #include <stdexcept>
 
+#include <yoga/config/Config.h>
 #include <yoga/debug/AssertFatal.h>
 #include <yoga/debug/Log.h>
+#include <yoga/node/Node.h>
 
 namespace facebook::yoga {
 

yoga/debug/AssertFatal.h

@@ -8,11 +8,12 @@
 #pragma once
 
 #include <yoga/Yoga.h>
-#include <yoga/config/Config.h>
-#include <yoga/node/Node.h>
 
 namespace facebook::yoga {
 
+class Node;
+class Config;
+
 [[noreturn]] void fatalWithMessage(const char* message);
 
 void assertFatal(bool condition, const char* message);

yoga/node/CachedMeasurement.h

@@ -11,7 +11,7 @@
 
 #include <yoga/Yoga.h>
 
-#include <yoga/enums/MeasureMode.h>
+#include <yoga/algorithm/SizingMode.h>
 #include <yoga/numeric/Comparison.h>
 
 namespace facebook::yoga {
@@ -19,15 +19,15 @@ namespace facebook::yoga {
 struct CachedMeasurement {
   float availableWidth{-1};
   float availableHeight{-1};
-  MeasureMode widthMeasureMode{MeasureMode::Undefined};
-  MeasureMode heightMeasureMode{MeasureMode::Undefined};
+  SizingMode widthSizingMode{SizingMode::MaxContent};
+  SizingMode heightSizingMode{SizingMode::MaxContent};
 
   float computedWidth{-1};
   float computedHeight{-1};
 
   bool operator==(CachedMeasurement measurement) const {
-    bool isEqual = widthMeasureMode == measurement.widthMeasureMode &&
-        heightMeasureMode == measurement.heightMeasureMode;
+    bool isEqual = widthSizingMode == measurement.widthSizingMode &&
+        heightSizingMode == measurement.heightSizingMode;
 
     if (!yoga::isUndefined(availableWidth) ||
         !yoga::isUndefined(measurement.availableWidth)) {