Bug 1476127: Implement 'contain:size' for select elements. r=TYLin

Note that this is an imperfect implementation, in that it doesn't exactly
match the sizing behavior of a truly empty `<select>` element.  I've filed
followup bug 1562057 on that.  However, the behavior that's implemented
here *does* successfully make us ignore a `<select>`'s contents for sizing
purposes, and it's much better than what we do currently (which is pretty
broken via inheriting a partial `contain:size` implementation from our
parent class, nsBlockFrame).

Differential Revision: https://phabricator.services.mozilla.com/D36253

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

layout/forms/nsComboboxControlFrame.cpp

@@ -716,8 +716,9 @@ nscoord nsComboboxControlFrame::GetIntrinsicISize(
         presContext, aRenderingContext, GetWritingMode());
   }
 
+  const bool isContainSize = StyleDisplay()->IsContainSize();
   nscoord displayISize = 0;
-  if (MOZ_LIKELY(mDisplayFrame)) {
+  if (MOZ_LIKELY(mDisplayFrame) && !isContainSize) {
     displayISize = nsLayoutUtils::IntrinsicForContainer(aRenderingContext,
                                                         mDisplayFrame, aType);
   }
@@ -727,13 +728,15 @@ nscoord nsComboboxControlFrame::GetIntrinsicISize(
     bool isUsingOverlayScrollbars =
         LookAndFeel::GetInt(LookAndFeel::eIntID_UseOverlayScrollbars) != 0;
     if (aType == nsLayoutUtils::MIN_ISIZE) {
-      dropdownContentISize = mDropdownFrame->GetMinISize(aRenderingContext);
+      dropdownContentISize =
+          isContainSize ? 0 : mDropdownFrame->GetMinISize(aRenderingContext);
       if (isUsingOverlayScrollbars) {
         dropdownContentISize += scrollbarWidth;
       }
     } else {
       NS_ASSERTION(aType == nsLayoutUtils::PREF_ISIZE, "Unexpected type");
-      dropdownContentISize = mDropdownFrame->GetPrefISize(aRenderingContext);
+      dropdownContentISize =
+          isContainSize ? 0 : mDropdownFrame->GetPrefISize(aRenderingContext);
       if (isUsingOverlayScrollbars) {
         dropdownContentISize += scrollbarWidth;
       }

layout/generic/nsBlockFrame.cpp

@@ -1861,11 +1861,20 @@ void nsBlockFrame::ComputeFinalSize(const ReflowInput& aReflowInput,
 
     // Don't carry out a block-end margin when our BSize is fixed.
     aMetrics.mCarriedOutBEndMargin.Zero();
-  } else if (aReflowInput.mStyleDisplay->IsContainSize()) {
+  } else if (!IsComboboxControlFrame() &&
+             aReflowInput.mStyleDisplay->IsContainSize()) {
     // If we're size-containing and we don't have a specified size, then our
     // final size should actually be computed from only our border and padding,
     // as though we were empty.
     // Hence this case is a simplified version of the case below.
+    //
+    // NOTE: We exempt the nsComboboxControlFrame subclass from taking this
+    // special case, because comboboxes implicitly honors the size-containment
+    // behavior on its nsComboboxDisplayFrame child (which it shrinkwraps)
+    // rather than on the nsComboboxControlFrame. (Moreover, the DisplayFrame
+    // child doesn't even need any special content-size-ignoring behavior in
+    // its reflow method, because that method just resolves "auto" BSize values
+    // to one line-height rather than by measuring its contents' BSize.)
     nscoord contentBSize = 0;
     nscoord autoBSize = aReflowInput.ApplyMinMaxBSize(contentBSize);
     aMetrics.mCarriedOutBEndMargin.Zero();

layout/reftests/w3c-css/submitted/contain/reftest.list

@@ -35,8 +35,8 @@ fuzzy-if(webrender&&winWidget,0-24,0-2) == contain-size-inline-flex-001.html con
 == contain-size-fieldset-002.html contain-size-fieldset-002-ref.html
 == contain-size-multicol-002.html contain-size-multicol-002-ref.html
 == contain-size-multicol-003.html contain-size-multicol-003-ref.html
-fails == contain-size-select-elem-001.html contain-size-select-elem-001-ref.html # bug 1476127
-fails == contain-size-select-elem-002.html contain-size-select-elem-002-ref.html # bug 1476127
+fuzzy-if(Android,0-4,0-4) == contain-size-select-elem-001.html contain-size-select-elem-001-ref.html # bug 1480862
+fails-if(!gtkWidget) == contain-size-select-elem-002.html contain-size-select-elem-002-ref.html # bug 1562057
 == contain-layout-overflow-001.html contain-layout-overflow-001-ref.html
 == contain-layout-overflow-002.html contain-layout-overflow-002-ref.html
 == contain-size-table-caption-001.html contain-size-table-caption-001-ref.html