Compute margin block start for 1st block in LayoutNG root constraint space

third_party/WebKit/Source/core/layout/ng/ng_box.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ng/ng_box.h"
 
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/layout/ng/layout_ng_block_flow.h"
 #include "core/layout/ng/ng_block_layout_algorithm.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_direction.h"
 #include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_fragment_builder.h"
 #include "core/layout/ng/ng_length_utils.h"
 #include "core/layout/ng/ng_writing_mode.h"
 
 namespace blink {
+namespace {
+// TODO(layout-ng): Add m_isNewBfc flag to ComputedStyle and set it from
+// StyleResolver instead of getting it calculated by createsNewFormattingContext
+bool isNewBlockFormattingContext(const LayoutBox* layout_box) {

[ikilpatrick, 2016/09/29 00:18:11]

I went and read through some of the specs, the best terminology here is:

establishesFormattingContext (or createsNewFormattingContext is also ok).

this doesn't just check for block formatting context so needs to be more
general.

[cbiesinger, 2016/09/29 00:41:28]

nit: Shouldn't this function start with an uppercase character?

[Gleb Lanbin, 2016/09/29 17:11:15]

Done.

[Gleb Lanbin, 2016/09/29 17:11:15]

Done.

+  return layout_box && toLayoutBlock(layout_box)->createsNewFormattingContext();
+}
+}  // namespace
+
 NGBox::NGBox(LayoutObject* layout_object)
     : layout_box_(toLayoutBox(layout_object)) {
   DCHECK(layout_box_);
 }
 
 NGBox::NGBox(ComputedStyle* style) : layout_box_(nullptr), style_(style) {
   DCHECK(style_);
 }
 
 bool NGBox::Layout(const NGConstraintSpace* constraint_space,
                    NGFragment** out) {
   if (layout_box_ && layout_box_->isOutOfFlowPositioned())
     layout_box_->containingBlock()->insertPositionedObject(layout_box_);
   // We can either use the new layout code to do the layout and then copy the
   // resulting size to the LayoutObject, or use the old layout code and
   // synthesize a fragment.
   if (CanUseNewLayout()) {
     if (!algorithm_)
       algorithm_ = new NGBlockLayoutAlgorithm(Style(), FirstChild());
     // Change the coordinate system of the constraint space.
     NGConstraintSpace* child_constraint_space = new NGConstraintSpace(
         FromPlatformWritingMode(Style()->getWritingMode()),
         FromPlatformDirection(Style()->direction()), constraint_space);
+    child_constraint_space->SetIsNewBfc(
+        isNewBlockFormattingContext(layout_box_));
 
     NGPhysicalFragment* fragment = nullptr;
     if (!algorithm_->Layout(child_constraint_space, &fragment))
       return false;
     fragment_ = fragment;
 
     if (layout_box_) {
       layout_box_->setWidth(fragment_->Width());
       layout_box_->setHeight(fragment_->Height());
       NGBoxStrut border_and_padding =
@@ skipping 98 matching lines @@
 
 bool NGBox::CanUseNewLayout() {
   if (!layout_box_)
     return true;
   if (!layout_box_->isLayoutBlockFlow())
     return false;
   const LayoutBlockFlow* block_flow = toLayoutBlockFlow(layout_box_);
   return !block_flow->childrenInline() || !block_flow->firstChild();
 }
 }  // namespace blink