Bug 666041 patch 8: Add special handling for "min-width: auto" value on flex items. r=dbaron

layout/generic/nsHTMLReflowState.cpp

@@ -2502,10 +2502,22 @@ nsHTMLReflowState::ComputeMinMaxValues(nscoord aContainingBlockWidth,
                                        nscoord aContainingBlockHeight,
                                        const nsHTMLReflowState* aContainingBlockRS)
 {
+#ifdef MOZ_FLEXBOX
+  nsFlexContainerFrame* flexContainerFrame = GetFlexContainer(frame);
+#endif // MOZ_FLEXBOX
+
   // Handle "min-width: auto"
   if (eStyleUnit_Auto == mStylePosition->mMinWidth.GetUnit()) {
-    // XXXdholbert For flex items, this needs to behave like -moz-min-content.
     mComputedMinWidth = 0;
+#ifdef MOZ_FLEXBOX
+    if (flexContainerFrame && flexContainerFrame->IsHorizontal()) {
+      mComputedMinWidth =
+        ComputeWidthValue(aContainingBlockWidth,
+                          mStylePosition->mBoxSizing,
+                          nsStyleCoord(NS_STYLE_WIDTH_MIN_CONTENT,
+                                       eStyleUnit_Enumerated));
+    }
+#endif // MOZ_FLEXBOX
   } else {
     mComputedMinWidth = ComputeWidthValue(aContainingBlockWidth,
                                           mStylePosition->mBoxSizing,

layout/style/nsComputedDOMStyle.cpp

@@ -23,6 +23,7 @@
 #include "nsCSSProps.h"
 #include "nsCSSKeywords.h"
 #include "nsDOMCSSRect.h"
+#include "nsFlexContainerFrame.h"
 #include "nsGkAtoms.h"
 #include "nsHTMLReflowState.h"
 #include "nsThemeConstants.h"
@@ -3388,12 +3389,22 @@ nsComputedDOMStyle::DoGetMinWidth()
   nsStyleCoord minWidth = GetStylePosition()->mMinWidth;
 
   if (eStyleUnit_Auto == minWidth.GetUnit()) {
-    // In non-flexbox contexts, "min-width: auto" means "min-width: 0".
-    // XXXdholbert For flex items, we should set |minWidth| to the
-    // -moz-min-content keyword, instead of 0.
+    // "min-width: auto" means "0", unless we're a flex item in a horizontal
+    // flex container, in which case it means "min-content"
     minWidth.SetCoordValue(0);
-  }
+#ifdef MOZ_FLEXBOX
+    if (mOuterFrame && mOuterFrame->IsFlexItem()) {
+      nsIFrame* flexContainer = mOuterFrame->GetParent();
+      MOZ_ASSERT(flexContainer &&
+                 flexContainer->GetType() == nsGkAtoms::flexContainerFrame,
+                 "IsFlexItem() lied...?");
 
+      if (static_cast<nsFlexContainerFrame*>(flexContainer)->IsHorizontal()) {
+        minWidth.SetIntValue(NS_STYLE_WIDTH_MIN_CONTENT, eStyleUnit_Enumerated);
+      }
+    }
+#endif // MOZ_FLEXBOX
+  }
   SetValueToCoord(val, minWidth, true,
                   &nsComputedDOMStyle::GetCBContentWidth,
                   nsCSSProps::kWidthKTable);