Bug 1312379 part 2 - [css-flexbox] Improve support for CSS Alignment 'last baseline' alignment by exporting the last baseline when asked for. r=dholbert

layout/generic/nsFlexContainerFrame.cpp

@@ -4542,9 +4542,6 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
     aDesiredSize.SetBlockStartAscent(flexContainerAscent);
   }
 
-  // Cache this baseline for use outside of this call.
-  mBaselineFromLastReflow = flexContainerAscent;
-
   // Now: If we're complete, add bottom border/padding to desired height (which
   // we skipped via skipSides) -- unless that pushes us over available height,
   // in which case we become incomplete (unless we already weren't asking for
@@ -4568,6 +4565,16 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
     }
   }
 
+  // Calculate the container baselines so that our parent can baseline-align us.
+  mBaselineFromLastReflow = flexContainerAscent;
+  mLastBaselineFromLastReflow = lines.getLast()->GetLastBaselineOffset();
+  if (mLastBaselineFromLastReflow == nscoord_MIN) {
+    // XXX we fall back to a mirrored first baseline here for now, but this
+    // should probably use the last baseline of the last item or something.
+    mLastBaselineFromLastReflow =
+      desiredSizeInFlexWM.BSize(flexWM) - flexContainerAscent;
+  }
+
   // Convert flex container's final desired size to parent's WM, for outparam.
   aDesiredSize.SetSize(flexWM, desiredSizeInFlexWM);
 

layout/generic/nsFlexContainerFrame.h

@@ -96,7 +96,8 @@ public:
     if (HasAnyStateBits(NS_STATE_FLEX_SYNTHESIZE_BASELINE)) {
       return false;
     }
-    *aBaseline = GetLogicalBaseline(aWM);
+    *aBaseline = aBaselineGroup == BaselineSharingGroup::eFirst ?
+                   mBaselineFromLastReflow : mLastBaselineFromLastReflow;
     return true;
   }
 
@@ -133,6 +134,7 @@ protected:
   explicit nsFlexContainerFrame(nsStyleContext* aContext)
     : nsContainerFrame(aContext)
     , mBaselineFromLastReflow(NS_INTRINSIC_WIDTH_UNKNOWN)
+    , mLastBaselineFromLastReflow(NS_INTRINSIC_WIDTH_UNKNOWN)
   {}
   virtual ~nsFlexContainerFrame();
 
@@ -318,6 +320,8 @@ protected:
                                    // to satisfy their 'order' values?
 
   nscoord mBaselineFromLastReflow;
+  // Note: the last baseline is a distance from our border-box end edge.
+  nscoord mLastBaselineFromLastReflow;
 };
 
 #endif /* nsFlexContainerFrame_h___ */