[layoutng] Support computing min-content and max-content

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

Index: third_party/WebKit/Source/core/layout/ng/ng_box.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_box.cc b/third_party/WebKit/Source/core/layout/ng/ng_box.cc
index 40062d95e97e529b9d4adec139b79c4ada13e61d..6e430da1e2ece72a56a513d3652539d60b4a3b49 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_box.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_box.cc
@@ -7,6 +7,7 @@
 #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_builder.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_direction.h"
 #include "core/layout/ng/ng_fragment.h"
@@ -63,6 +64,66 @@ bool NGBox::Layout(const NGConstraintSpace* constraint_space,
   return true;
 }
 
+bool NGBox::ComputeOrSynthesizeMinAndMaxContentSizes(

[atotic, 2016/11/01 21:56:02]

This routine name is 41 chars long, 1/2 of our line budget.
Suggestion:
// Use comment to describe Synthesize
Rename to ComputeMinMaxContentSizes

[cbiesinger, 2016/11/02 20:18:08]

Ok, I renamed it back to ComputeMinAndMaxContentSizes. Note that Gleb requested
the rename earlier. However, NGBox::Layout does have differences from
NGBlockLayoutAlgorithm::Layout as well, so maybe the same name is not so bad.

+    MinAndMaxContentSizes* sizes) {
+  if (!algorithm_) {
+    NGConstraintSpaceBuilder builder(
+        FromPlatformWritingMode(Style()->getWritingMode()));
+
+    builder.SetContainerSize(NGLogicalSize(LayoutUnit(), LayoutUnit()));
+    // TODO(layoutng): Use builder.ToConstraintSpace.ToLogicalConstraintSpace
+    // once
+    // that's available.
+    NGConstraintSpace* constraint_space = new NGConstraintSpace(
+        FromPlatformWritingMode(Style()->getWritingMode()),
+        FromPlatformDirection(Style()->direction()),
+        builder.ToConstraintSpace());
+
+    algorithm_ =

[atotic, 2016/11/01 21:56:02]

algorithm_ is used in 2 functions (Layout & MinMax) for different purposes. This
can lead to hard-to-debug error if caller interleaves them (as you noted in
.h:37 docs). Suggestion:

have two different algorithm_ members (_layout_algorithm, _minmax_algorithm).

Inside Layout, DCHECK(_minmax == null)
Inside MinMax, DCHECK(_layout == null)

This would catch the error if it happens.

[cbiesinger, 2016/11/02 20:18:08]

OK -- I will do that for now. Once we have the state machine we can maybe use
the state variable for a similar assert and don't need to store two layout
algorithms.

+        new NGBlockLayoutAlgorithm(Style(), FirstChild(), constraint_space);
+  }
+  // TODO(cbiesinger): For orthogonal children, we need to always synthesize.
+  NGLayoutAlgorithm::MinAndMaxState state =
+      algorithm_->ComputeMinAndMaxContentSizes(sizes);
+  if (state == NGLayoutAlgorithm::Success)
+    return true;
+  if (state == NGLayoutAlgorithm::Pending)
+    return false;
+  DCHECK_EQ(state, NGLayoutAlgorithm::NotImplemented);
+
+  // TODO(cbiesinger): Replace the loops below with a state machine like in
+  // Layout.
+
+  // Have to synthesize this value.
+  NGPhysicalFragment* physical_fragment;
+  while (!algorithm_->Layout(&physical_fragment))
+    continue;
+  NGFragment* fragment = new NGFragment(
+      FromPlatformWritingMode(Style()->getWritingMode()),
+      FromPlatformDirection(Style()->direction()), physical_fragment);
+
+  sizes->min_content = fragment->InlineOverflow();
+
+  // Now, redo with infinite space for max_content
+  NGConstraintSpaceBuilder builder(
+      FromPlatformWritingMode(Style()->getWritingMode()));
+  builder.SetContainerSize(NGLogicalSize(LayoutUnit::max(), LayoutUnit()));
+  NGConstraintSpace* constraint_space = new NGConstraintSpace(
+      FromPlatformWritingMode(Style()->getWritingMode()),
+      FromPlatformDirection(Style()->direction()), builder.ToConstraintSpace());
+
+  algorithm_ =
+      new NGBlockLayoutAlgorithm(Style(), FirstChild(), constraint_space);
+  while (!algorithm_->Layout(&physical_fragment))
+    continue;
+
+  fragment = new NGFragment(FromPlatformWritingMode(Style()->getWritingMode()),
+                            FromPlatformDirection(Style()->direction()),
+                            physical_fragment);
+  sizes->max_content = fragment->InlineOverflow();
+  return true;
+}
+
 const ComputedStyle* NGBox::Style() const {
   if (style_)
     return style_.get();
@@ -97,6 +158,13 @@ void NGBox::SetFirstChild(NGBox* child) {
   first_child_ = child;
 }
 
+DEFINE_TRACE(NGBox) {
+  visitor->trace(algorithm_);
+  visitor->trace(fragment_);
+  visitor->trace(next_sibling_);
+  visitor->trace(first_child_);
+}
+
 void NGBox::PositionUpdated() {
   if (!layout_box_)
     return;