Use CSS terminology for sizing rules (facebook#1460)

Summary:
X-link: facebook/react-native#41390


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

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,