Bug 1501109 Part 1: Change Flex API growth state to match layout algorithm, and use enums from webidl. r=dholbert

Differential Revision: https://phabricator.services.mozilla.com/D9454

--HG--
extra : moz-landing-system : lando

dom/chrome-webidl/Flex.webidl

@@ -39,10 +39,17 @@ interface Flex
 };
 
 /**
- * Lines with items that have been shrunk are shrinking; with items
- * that have grown are growing, and all others are unchanged.
+ * This indicates which flex factor (flex-grow vs. flex-shrink) the
+ * flex layout algorithm uses internally when resolving flexible sizes
+ * in a given flex line, per flexbox spec section 9.7 step 1. Note that
+ * this value doesn't necessarily mean that any items on this line
+ * are *actually* growing (or shrinking).  This simply indicates what
+ * the layout algorithm "wants" to do, based on the free space -- 
+ * and items will stretch from their flex base size in the corresponding
+ * direction, if permitted by their min/max constraints and their
+ * corresponding flex factor.
  */
-enum FlexLineGrowthState { "unchanged", "shrinking", "growing" };
+enum FlexLineGrowthState { "shrinking", "growing" };
 
 [ChromeOnly]
 interface FlexLineValues

dom/flex/FlexLineValues.cpp

@@ -30,18 +30,7 @@ FlexLineValues::FlexLineValues(Flex* aParent,
 
   // Eagerly copy values from aLine, because we're not
   // going to keep it around.
-  switch (aLine->mGrowthState) {
-    case ComputedFlexLineInfo::GrowthState::SHRINKING:
-      mGrowthState = FlexLineGrowthState::Shrinking;
-      break;
-
-    case ComputedFlexLineInfo::GrowthState::GROWING:
-      mGrowthState = FlexLineGrowthState::Growing;
-      break;
-
-    default:
-      mGrowthState = FlexLineGrowthState::Unchanged;
-  };
+  mGrowthState = aLine->mGrowthState;
 
   // Convert all the app unit values into css pixels.
   mCrossStart = nsPresContext::AppUnitsToDoubleCSSPixels(

layout/generic/nsFlexContainerFrame.cpp

@@ -2643,6 +2643,12 @@ FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize,
   const bool isUsingFlexGrow =
     (mTotalOuterHypotheticalMainSize < aFlexContainerMainSize);
 
+  if (aLineInfo) {
+    aLineInfo->mGrowthState = isUsingFlexGrow ?
+                              mozilla::dom::FlexLineGrowthState::Growing :
+                              mozilla::dom::FlexLineGrowthState::Shrinking;
+  }
+
   // Do an "early freeze" for flex items that obviously can't flex in the
   // direction we've chosen:
   FreezeItemsEarly(isUsingFlexGrow, aLineInfo);
@@ -2872,30 +2878,6 @@ FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize,
                 aLineInfo->mItems[itemIndex].mMainBaseSize;
 
               aLineInfo->mItems[itemIndex].mMainDeltaSize = deltaSize;
-              // If any (unfrozen) item on the line is growing, we mark the
-              // aLineInfo structure; likewise if any item is shrinking.
-              // (Note: a line can't contain a mix of items that are growing
-              // and shrinking. Also, the sign of any delta should match the
-              // type of flex factor we're using [grow vs shrink].)
-              if (deltaSize > 0) {
-                MOZ_ASSERT(isUsingFlexGrow,
-                           "Unfrozen items can only grow if we're "
-                           "distributing (positive) space with flex-grow");
-                MOZ_ASSERT(aLineInfo->mGrowthState !=
-                           ComputedFlexLineInfo::GrowthState::SHRINKING,
-                           "shouldn't flip flop from shrinking to growing");
-                aLineInfo->mGrowthState =
-                  ComputedFlexLineInfo::GrowthState::GROWING;
-              } else if (deltaSize < 0) {
-                MOZ_ASSERT(!isUsingFlexGrow,
-                           "Unfrozen items can only shrink if we're "
-                           "distributing (negative) space with flex-shrink");
-                MOZ_ASSERT(aLineInfo->mGrowthState !=
-                           ComputedFlexLineInfo::GrowthState::GROWING,
-                           "shouldn't flip flop from growing to shrinking");
-                aLineInfo->mGrowthState =
-                  ComputedFlexLineInfo::GrowthState::SHRINKING;
-              }
             }
           }
         }
@@ -4770,16 +4752,10 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
          line = line->getNext()) {
       ComputedFlexLineInfo* lineInfo =
         containerInfo->mLines.AppendElement();
-      // Most lineInfo properties will be set later, but we set
-      // mGrowthState to UNCHANGED here because it may be later
-      // modified by ResolveFlexibleLengths().
-      lineInfo->mGrowthState =
-        ComputedFlexLineInfo::GrowthState::UNCHANGED;
-
-      // The remaining lineInfo properties will be filled out at the
-      // end of this function, when we have real values. But we still
-      // add all the items here, so we can capture computed data for
-      // each item.
+      // Most of the remaining lineInfo properties will be filled out at the
+      // end of this function (some will be provided by other functions),
+      // when we have real values. But we still add all the items here, so
+      // we can capture computed data for each item as we proceed.
       for (const FlexItem* item = line->GetFirstItem(); item;
            item = item->getNext()) {
         nsIFrame* frame = item->Frame();

layout/generic/nsFlexContainerFrame.h

@@ -63,11 +63,7 @@ struct ComputedFlexLineInfo
   nscoord mCrossSize;
   nscoord mFirstBaselineOffset;
   nscoord mLastBaselineOffset;
-  enum GrowthState {
-    UNCHANGED,
-    SHRINKING,
-    GROWING,
-  } mGrowthState;
+  mozilla::dom::FlexLineGrowthState mGrowthState;
 };
 
 struct ComputedFlexContainerInfo