[LayoutNG] Fix orthogonal writing mode child margin strut from being used in collapsing margins cal…

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.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_block_layout_algorithm.h"
 
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_fragment_builder.h"
 #include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_length_utils.h"
 #include "core/layout/ng/ng_units.h"
 #include "core/style/ComputedStyle.h"
 #include "platform/LengthFunctions.h"
 
 namespace blink {
 namespace {
 
 LayoutUnit ComputeCollapsedMarginBlockStart(
     const NGMarginStrut& prev_margin_strut,
     const NGMarginStrut& curr_margin_strut) {
   return std::max(prev_margin_strut.margin_block_end,
                   curr_margin_strut.margin_block_start) -
          std::max(prev_margin_strut.negative_margin_block_end.abs(),
                   curr_margin_strut.negative_margin_block_start.abs());
 }
 
+// Returns true if a in-flow block-level child creates a new formatting context.

[Gleb Lanbin, 2016/10/18 22:54:10]

.nit if a function returns boolean then google3 code style recommends to start a
doc string with "whether". Example: Whether an in-flow block-level child ...

[ikilpatrick, 2016/10/18 22:59:28]

Done, thanks!

+//
+// This will *NOT* check the following cases:
+//  - The child is out-of-flow, e.g. floating or abs-pos.
+//  - The child is a inline-level, e.g. "display: inline-block".
+//  - The child establishes a new formatting context, but should be a child of
+//    another layout algorithm, e.g. "display: table-caption" or flex-item.
+bool IsNewFormattingContextForInFlowBlockLevelChild(
+    const NGConstraintSpace& space,
+    const ComputedStyle& style) {
+  // TODO(layout-dev): This doesn't capture a few cases which can't be computed
+  // directly from style yet:
+  //  - The child is a <fieldset>.
+  //  - "column-span: all" is set on the child (requires knowledge that we are
+  //    in a multi-col formatting context).
+  //    (https://drafts.csswg.org/css-multicol-1/#valdef-column-span-all)
+
+  if (style.specifiesColumns() || style.containsPaint() ||
+      style.containsLayout())
+    return true;
+
+  if (!style.isOverflowVisible())
+    return true;
+
+  EDisplay display = style.display();
+  if (display == EDisplay::Grid || display == EDisplay::Flex ||
+      display == EDisplay::Box)
+    return true;
+
+  if (space.WritingMode() != FromPlatformWritingMode(style.getWritingMode()))
+    return true;
+
+  return false;
+}
+
 }  // namespace
 
 NGBlockLayoutAlgorithm::NGBlockLayoutAlgorithm(
     PassRefPtr<const ComputedStyle> style,
     NGBox* first_child)
     : style_(style),
       first_child_(first_child),
       state_(kStateInit),
       is_fragment_margin_strut_block_start_updated_(false) {
   DCHECK(style_);
@@ skipping 29 matching lines @@
       builder_ = new NGFragmentBuilder(NGPhysicalFragmentBase::FragmentBox);
       builder_->SetDirection(constraint_space->Direction());
       builder_->SetWritingMode(constraint_space->WritingMode());
       builder_->SetInlineSize(inline_size).SetBlockSize(block_size);
       current_child_ = first_child_;
       state_ = kStateChildLayout;
       return false;
     }
     case kStateChildLayout: {
       if (current_child_) {
+        constraint_space_for_children_->SetIsNewFormattingContext(
+            IsNewFormattingContextForInFlowBlockLevelChild(
+                *constraint_space, *current_child_->Style()));
+
         NGFragment* fragment;
         if (!current_child_->Layout(constraint_space_for_children_, &fragment))
           return false;
         NGBoxStrut child_margins = computeMargins(
             *constraint_space_for_children_, *current_child_->Style(),
             constraint_space_for_children_->WritingMode(),
             constraint_space_for_children_->Direction());
         ApplyAutoMargins(*constraint_space_for_children_,
                          *current_child_->Style(), *fragment, child_margins);
 
@@ skipping 107 matching lines @@
 
 void NGBlockLayoutAlgorithm::UpdateMarginStrut(const NGMarginStrut& from) {
   if (!is_fragment_margin_strut_block_start_updated_) {
     builder_->SetMarginStrutBlockStart(from);
     is_fragment_margin_strut_block_start_updated_ = true;
   }
   builder_->SetMarginStrutBlockEnd(from);
 }
 
 }  // namespace blink