Auto merge of #7312 - servo:flex-experimental, r=SimonSapin

Initial (very rudimentary) flexbox implementation.

This is #7154 with two additional commits (that I did rather than ask @zentner-kyle to do it because it was a bit tricky.)

r? @pcwalton for the last two commit

r=me+pcwalton in #7154 for earlier commits.

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components/layout/construct.rs

@@ -16,6 +16,7 @@
 use block::BlockFlow;
 use context::LayoutContext;
 use data::{HAS_NEWLY_CONSTRUCTED_FLOW, LayoutDataWrapper};
+use flex::FlexFlow;
 use floats::FloatKind;
 use flow::{MutableFlowUtils, MutableOwnedFlowUtils};
 use flow::{self, AbsoluteDescendants, Flow, ImmutableFlowUtils, IS_ABSOLUTELY_POSITIONED};
@@ -1277,6 +1278,14 @@ impl<'a> FlowConstructor<'a> {
         ConstructionResult::Flow(flow, AbsoluteDescendants::new())
     }
 
+    /// Builds a flow for a node with 'display: flex'.
+    fn build_flow_for_flex(&mut self, node: &ThreadSafeLayoutNode, float_kind: Option<FloatKind>)
+                           -> ConstructionResult {
+        let fragment = self.build_fragment_for_block(node);
+        let flow = Arc::new(FlexFlow::from_fragment(fragment, float_kind));
+        self.build_flow_for_block_like(flow, node)
+    }
+
     /// Attempts to perform incremental repair to account for recent changes to this node. This
     /// can fail and return false, indicating that flows will need to be reconstructed.
     ///
@@ -1518,6 +1527,13 @@ impl<'a> PostorderNodeMutTraversal for FlowConstructor<'a> {
                 self.set_flow_construction_result(node, construction_result)
             }
 
+            // Flex items contribute flex flow construction results.
+            (display::T::flex, float_value, _) => {
+                let float_kind = FloatKind::from_property(float_value);
+                let construction_result = self.build_flow_for_flex(node, float_kind);
+                self.set_flow_construction_result(node, construction_result)
+            }
+
             // Block flows that are not floated contribute block flow construction results.
             //
             // TODO(pcwalton): Make this only trigger for blocks and handle the other `display`

components/layout/display_list_builder.rs

@@ -13,6 +13,7 @@
 use azure::azure_hl::Color;
 use block::BlockFlow;
 use context::LayoutContext;
+use flex::FlexFlow;
 use flow::{self, BaseFlow, Flow, IS_ABSOLUTELY_POSITIONED, NEEDS_LAYER};
 use flow_ref;
 use fragment::{CoordinateSystem, Fragment, IframeFragmentInfo, ImageFragmentInfo};
@@ -1886,6 +1887,23 @@ impl ListItemFlowDisplayListBuilding for ListItemFlow {
     }
 }
 
+pub trait FlexFlowDisplayListBuilding {
+    fn build_display_list_for_flex(&mut self,
+                                   display_list: Box<DisplayList>,
+                                   layout_context: &LayoutContext);
+}
+
+impl FlexFlowDisplayListBuilding for FlexFlow {
+    fn build_display_list_for_flex(&mut self,
+                                   display_list: Box<DisplayList>,
+                                   layout_context: &LayoutContext) {
+        // Draw the rest of the block.
+        self.as_mut_block().build_display_list_for_block(display_list,
+                                                         layout_context,
+                                                         BorderPaintingMode::Separate)
+    }
+}
+
 trait BaseFlowDisplayListBuilding {
     fn build_display_items_for_debugging_tint(&self,
                                               display_list: &mut DisplayList,

components/layout/flex.rs

@@ -0,0 +1,446 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Layout for elements with a CSS `display` property of `flex`.
+
+#![deny(unsafe_code)]
+
+use block::BlockFlow;
+use context::LayoutContext;
+use display_list_builder::FlexFlowDisplayListBuilding;
+use floats::FloatKind;
+use flow;
+use flow::INLINE_POSITION_IS_STATIC;
+use flow::IS_ABSOLUTELY_POSITIONED;
+use flow::ImmutableFlowUtils;
+use flow::mut_base;
+use flow::{Flow, FlowClass, OpaqueFlow};
+use flow::{HAS_LEFT_FLOATED_DESCENDANTS, HAS_RIGHT_FLOATED_DESCENDANTS};
+use fragment::{Fragment, FragmentBorderBoxIterator};
+use incremental::{REFLOW, REFLOW_OUT_OF_FLOW};
+use layout_debug;
+use model::{IntrinsicISizes};
+use style::computed_values::{flex_direction, float};
+use style::properties::style_structs;
+use style::values::computed::LengthOrPercentageOrAuto;
+
+use euclid::{Point2D, Rect};
+use gfx::display_list::DisplayList;
+use model::MaybeAuto;
+use std::cmp::max;
+use std::sync::Arc;
+use style::properties::ComputedValues;
+use util::geometry::Au;
+use util::logical_geometry::LogicalSize;
+use util::opts;
+
+// A mode describes which logical axis a flex axis is parallel with.
+// The logical axises are inline and block, the flex axises are main and cross.
+// When the flex container has flex-direction: column or flex-direction: column-reverse, the main axis
+// should be block. Otherwise, it should be inline.
+#[derive(Debug)]
+enum Mode {
+    Inline,
+    Block
+}
+
+/// A block with the CSS `display` property equal to `flex`.
+#[derive(Debug)]
+pub struct FlexFlow {
+    /// Data common to all block flows.
+    block_flow: BlockFlow,
+    /// The logical axis which the main axis will be parallel with.
+    /// The cross axis will be parallel with the opposite logical axis.
+    main_mode: Mode,
+}
+
+fn flex_style(fragment: &Fragment) -> &style_structs::Flex {
+    fragment.style.get_flex()
+}
+
+// TODO(zentner): This function should use flex-basis.
+fn flex_item_inline_sizes(flow: &mut Flow) -> IntrinsicISizes {
+    let _scope = layout_debug_scope!("flex::flex_item_inline_sizes");
+    debug!("flex_item_inline_sizes");
+    let base = flow::mut_base(flow);
+
+    debug!("FlexItem intrinsic inline sizes: {:?}, {:?}",
+           base.intrinsic_inline_sizes.minimum_inline_size,
+           base.intrinsic_inline_sizes.preferred_inline_size);
+
+    IntrinsicISizes {
+        minimum_inline_size: base.intrinsic_inline_sizes.minimum_inline_size,
+        preferred_inline_size: base.intrinsic_inline_sizes.preferred_inline_size,
+    }
+}
+
+impl FlexFlow {
+    pub fn from_fragment(fragment: Fragment,
+                         flotation: Option<FloatKind>)
+                         -> FlexFlow {
+
+        let main_mode = match flex_style(&fragment).flex_direction {
+            flex_direction::T::row_reverse    => Mode::Inline,
+            flex_direction::T::row            => Mode::Inline,
+            flex_direction::T::column_reverse => Mode::Block,
+            flex_direction::T::column         => Mode::Block
+        };
+
+        let this = FlexFlow {
+            block_flow: BlockFlow::from_fragment(fragment, flotation),
+            main_mode: main_mode
+        };
+
+        this
+    }
+
+    // TODO(zentner): This function should use flex-basis.
+    // Currently, this is the core of BlockFlow::bubble_inline_sizes() with all float logic
+    // stripped out, and max replaced with union_nonbreaking_inline.
+    fn inline_mode_bubble_inline_sizes(&mut self) {
+        let fixed_width = match self.block_flow.fragment.style().get_box().width {
+            LengthOrPercentageOrAuto::Length(_) => true,
+            _ => false,
+        };
+
+        let mut computation = self.block_flow.fragment.compute_intrinsic_inline_sizes();
+        if !fixed_width {
+            for kid in self.block_flow.base.child_iter() {
+                let is_absolutely_positioned =
+                    flow::base(kid).flags.contains(IS_ABSOLUTELY_POSITIONED);
+                if !is_absolutely_positioned {
+                    computation.union_nonbreaking_inline(&flex_item_inline_sizes(kid));
+                }
+            }
+        }
+        self.block_flow.base.intrinsic_inline_sizes = computation.finish();
+    }
+
+    // TODO(zentner): This function should use flex-basis.
+    // Currently, this is the core of BlockFlow::bubble_inline_sizes() with all float logic
+    // stripped out.
+    fn block_mode_bubble_inline_sizes(&mut self) {
+        let fixed_width = match self.block_flow.fragment.style().get_box().width {
+            LengthOrPercentageOrAuto::Length(_) => true,
+            _ => false,
+        };
+
+        let mut computation = self.block_flow.fragment.compute_intrinsic_inline_sizes();
+        if !fixed_width {
+            for kid in self.block_flow.base.child_iter() {
+                let is_absolutely_positioned =
+                    flow::base(kid).flags.contains(IS_ABSOLUTELY_POSITIONED);
+                let child_base = flow::mut_base(kid);
+                if !is_absolutely_positioned {
+                    computation.content_intrinsic_sizes.minimum_inline_size =
+                        max(computation.content_intrinsic_sizes.minimum_inline_size,
+                            child_base.intrinsic_inline_sizes.minimum_inline_size);
+
+                    computation.content_intrinsic_sizes.preferred_inline_size =
+                        max(computation.content_intrinsic_sizes.preferred_inline_size,
+                            child_base.intrinsic_inline_sizes.preferred_inline_size);
+                }
+            }
+        }
+        self.block_flow.base.intrinsic_inline_sizes = computation.finish();
+    }
+
+    // TODO(zentner): This function needs to be radically different for multi-line flexbox.
+    // Currently, this is the core of BlockFlow::propagate_assigned_inline_size_to_children() with
+    // all float and table logic stripped out.
+    fn block_mode_assign_inline_sizes(&mut self,
+                                      _layout_context: &LayoutContext,
+                                      inline_start_content_edge: Au,
+                                      inline_end_content_edge: Au,
+                                      content_inline_size: Au) {
+        let _scope = layout_debug_scope!("flex::block_mode_assign_inline_sizes");
+        debug!("block_mode_assign_inline_sizes");
+
+        // Calculate non-auto block size to pass to children.
+        let content_block_size = self.block_flow.fragment.style().content_block_size();
+
+        let explicit_content_size =
+            match (content_block_size, self.block_flow.base.block_container_explicit_block_size) {
+            (LengthOrPercentageOrAuto::Percentage(percent), Some(container_size)) => {
+                Some(container_size.scale_by(percent))
+            }
+            (LengthOrPercentageOrAuto::Percentage(_), None) |
+            (LengthOrPercentageOrAuto::Auto, _) => None,
+            (LengthOrPercentageOrAuto::Length(length), _) => Some(length),
+        };
+
+        // FIXME (mbrubeck): Get correct mode for absolute containing block
+        let containing_block_mode = self.block_flow.base.writing_mode;
+
+        let mut iterator = self.block_flow.base.child_iter().enumerate().peekable();
+        while let Some((_, kid)) = iterator.next() {
+            {
+                let kid_base = flow::mut_base(kid);
+                kid_base.block_container_explicit_block_size = explicit_content_size;
+            }
+
+            // The inline-start margin edge of the child flow is at our inline-start content edge,
+            // and its inline-size is our content inline-size.
+            let kid_mode = flow::base(kid).writing_mode;
+            {
+                let kid_base = flow::mut_base(kid);
+                if kid_base.flags.contains(INLINE_POSITION_IS_STATIC) {
+                    kid_base.position.start.i =
+                        if kid_mode.is_bidi_ltr() == containing_block_mode.is_bidi_ltr() {
+                            inline_start_content_edge
+                        } else {
+                            // The kid's inline 'start' is at the parent's 'end'
+                            inline_end_content_edge
+                        };
+                }
+                kid_base.block_container_inline_size = content_inline_size;
+                kid_base.block_container_writing_mode = containing_block_mode;
+            }
+        }
+    }
+
+    // TODO(zentner): This function should actually flex elements!
+    // Currently, this is the core of InlineFlow::propagate_assigned_inline_size_to_children() with
+    // fragment logic stripped out.
+    fn inline_mode_assign_inline_sizes(&mut self,
+                                       _layout_context: &LayoutContext,
+                                       inline_start_content_edge: Au,
+                                       _inline_end_content_edge: Au,
+                                       content_inline_size: Au) {
+        let _scope = layout_debug_scope!("flex::inline_mode_assign_inline_sizes");
+        debug!("inline_mode_assign_inline_sizes");
+
+        debug!("content_inline_size = {:?}", content_inline_size);
+        debug!("child_count = {:?}", ImmutableFlowUtils::child_count(self as &Flow) as i32);
+        let even_content_inline_size = content_inline_size / ImmutableFlowUtils::child_count(self as &Flow) as i32;
+
+        let inline_size = self.block_flow.base.block_container_inline_size;
+        let container_mode = self.block_flow.base.block_container_writing_mode;
+        self.block_flow.base.position.size.inline = inline_size;
+
+        let block_container_explicit_block_size = self.block_flow.base.block_container_explicit_block_size;
+        let mut inline_child_start = inline_start_content_edge;
+        for kid in self.block_flow.base.child_iter() {
+            let kid_base = flow::mut_base(kid);
+
+            kid_base.block_container_inline_size = even_content_inline_size;
+            kid_base.block_container_writing_mode = container_mode;
+            kid_base.block_container_explicit_block_size = block_container_explicit_block_size;
+            kid_base.position.start.i = inline_child_start;
+            inline_child_start = inline_child_start + even_content_inline_size;
+        }
+    }
+
+    // TODO(zentner): This function should actually flex elements!
+    fn block_mode_assign_block_size<'a>(&mut self, layout_context: &'a LayoutContext<'a>) {
+        self.block_flow.assign_block_size(layout_context)
+    }
+
+    // TODO(zentner): This function should actually flex elements!
+    // Currently, this is the core of TableRowFlow::assign_block_size() with
+    // float related logic stripped out.
+    fn inline_mode_assign_block_size<'a>(&mut self, layout_context: &'a LayoutContext<'a>) {
+        let _scope = layout_debug_scope!("flex::inline_mode_assign_block_size");
+
+        let mut max_block_size = Au(0);
+        let thread_id = self.block_flow.base.thread_id;
+        for kid in self.block_flow.base.child_iter() {
+            kid.assign_block_size_for_inorder_child_if_necessary(layout_context, thread_id);
+
+            {
+                let child_fragment = &mut kid.as_mut_block().fragment;
+                // TODO: Percentage block-size
+                let child_specified_block_size =
+                    MaybeAuto::from_style(child_fragment.style().content_block_size(),
+                                          Au(0)).specified_or_zero();
+                max_block_size =
+                    max(max_block_size,
+                        child_specified_block_size +
+                        child_fragment.border_padding.block_start_end());
+            }
+            let child_node = flow::mut_base(kid);
+            child_node.position.start.b = Au(0);
+            max_block_size = max(max_block_size, child_node.position.size.block);
+        }
+
+        let mut block_size = max_block_size;
+        // TODO: Percentage block-size
+
+        block_size = match MaybeAuto::from_style(self.block_flow
+                                                     .fragment
+                                                     .style()
+                                                     .content_block_size(),
+                                                 Au(0)) {
+            MaybeAuto::Auto => block_size,
+            MaybeAuto::Specified(value) => max(value, block_size),
+        };
+
+        // Assign the block-size of own fragment
+        let mut position = self.block_flow.fragment.border_box;
+        position.size.block = block_size;
+        self.block_flow.fragment.border_box = position;
+        self.block_flow.base.position.size.block = block_size;
+
+        // Assign the block-size of kid fragments, which is the same value as own block-size.
+        for kid in self.block_flow.base.child_iter() {
+            {
+                let kid_fragment = &mut kid.as_mut_block().fragment;
+                let mut position = kid_fragment.border_box;
+                position.size.block = block_size;
+                kid_fragment.border_box = position;
+            }
+
+            // Assign the child's block size.
+            flow::mut_base(kid).position.size.block = block_size
+        }
+    }
+}
+
+impl Flow for FlexFlow {
+    fn class(&self) -> FlowClass {
+        FlowClass::Flex
+    }
+
+    fn as_mut_block<'a>(&'a mut self) -> &'a mut BlockFlow {
+        &mut self.block_flow
+    }
+
+    fn bubble_inline_sizes(&mut self) {
+        let _scope = layout_debug_scope!("flex::bubble_inline_sizes {:x}",
+                                         self.block_flow.base.debug_id());
+
+        // Flexbox Section 9.0: Generate anonymous flex items:
+        // This part was handled in the flow constructor.
+
+        // Flexbox Section 9.1: Re-order the flex items (and any absolutely positioned flex
+        // container children) according to their order.
+        // TODO(zentner): We need to re-order the items at some point. However, all the operations
+        // here ignore order, so we can afford to do it later, if necessary.
+
+        // `flex item`s (our children) cannot be floated. Furthermore, they all establish BFC's.
+        // Therefore, we do not have to handle any floats here.
+
+        let mut flags = self.block_flow.base.flags;
+        flags.remove(HAS_LEFT_FLOATED_DESCENDANTS);
+        flags.remove(HAS_RIGHT_FLOATED_DESCENDANTS);
+
+        match self.main_mode {
+            Mode::Inline => self.inline_mode_bubble_inline_sizes(),
+            Mode::Block  => self.block_mode_bubble_inline_sizes()
+        }
+
+        // Although our children can't be floated, we can.
+        match self.block_flow.fragment.style().get_box().float {
+            float::T::none => {}
+            float::T::left => flags.insert(HAS_LEFT_FLOATED_DESCENDANTS),
+            float::T::right => flags.insert(HAS_RIGHT_FLOATED_DESCENDANTS),
+        }
+        self.block_flow.base.flags = flags
+    }
+
+    fn assign_inline_sizes(&mut self, layout_context: &LayoutContext) {
+        let _scope = layout_debug_scope!("flex::assign_inline_sizes {:x}", self.block_flow.base.debug_id());
+        debug!("assign_inline_sizes");
+
+        if !self.block_flow.base.restyle_damage.intersects(REFLOW_OUT_OF_FLOW | REFLOW) {
+            return
+        }
+
+        // Our inline-size was set to the inline-size of the containing block by the flow's parent.
+        // Now compute the real value.
+        let containing_block_inline_size = self.block_flow.base.block_container_inline_size;
+        self.block_flow.compute_used_inline_size(layout_context, containing_block_inline_size);
+        if self.block_flow.base.flags.is_float() {
+            self.block_flow.float.as_mut().unwrap().containing_inline_size = containing_block_inline_size
+        }
+
+        // Move in from the inline-start border edge.
+        let inline_start_content_edge = self.block_flow.fragment.border_box.start.i +
+            self.block_flow.fragment.border_padding.inline_start;
+
+        debug!("inline_start_content_edge = {:?}", inline_start_content_edge);
+
+        let padding_and_borders = self.block_flow.fragment.border_padding.inline_start_end();
+
+        // Distance from the inline-end margin edge to the inline-end content edge.
+        let inline_end_content_edge =
+            self.block_flow.fragment.margin.inline_end +
+            self.block_flow.fragment.border_padding.inline_end;
+
+        debug!("padding_and_borders = {:?}", padding_and_borders);
+        debug!("self.block_flow.fragment.border_box.size.inline = {:?}",
+               self.block_flow.fragment.border_box.size.inline);
+        let content_inline_size = self.block_flow.fragment.border_box.size.inline - padding_and_borders;
+
+        match self.main_mode {
+            Mode::Inline =>
+                self.inline_mode_assign_inline_sizes(layout_context,
+                                                     inline_start_content_edge,
+                                                     inline_end_content_edge,
+                                                     content_inline_size),
+            Mode::Block  =>
+                self.block_mode_assign_inline_sizes(layout_context,
+                                                    inline_start_content_edge,
+                                                    inline_end_content_edge,
+                                                    content_inline_size)
+        }
+    }
+
+    fn assign_block_size<'a>(&mut self, layout_context: &'a LayoutContext<'a>) {
+        self.block_flow.assign_block_size(layout_context);
+        match self.main_mode {
+            Mode::Inline =>
+                self.inline_mode_assign_block_size(layout_context),
+            Mode::Block  =>
+                self.block_mode_assign_block_size(layout_context)
+        }
+    }
+
+    fn compute_absolute_position(&mut self, layout_context: &LayoutContext) {
+        self.block_flow.compute_absolute_position(layout_context)
+    }
+
+    fn place_float_if_applicable<'a>(&mut self, layout_context: &'a LayoutContext<'a>) {
+        self.block_flow.place_float_if_applicable(layout_context)
+    }
+
+    fn update_late_computed_inline_position_if_necessary(&mut self, inline_position: Au) {
+        self.block_flow.update_late_computed_inline_position_if_necessary(inline_position)
+    }
+
+    fn update_late_computed_block_position_if_necessary(&mut self, block_position: Au) {
+        self.block_flow.update_late_computed_block_position_if_necessary(block_position)
+    }
+
+    fn build_display_list(&mut self, layout_context: &LayoutContext) {
+        self.build_display_list_for_flex(Box::new(DisplayList::new()), layout_context);
+
+        if opts::get().validate_display_list_geometry {
+            self.block_flow.base.validate_display_list_geometry();
+        }
+    }
+
+    fn repair_style(&mut self, new_style: &Arc<ComputedValues>) {
+        self.block_flow.repair_style(new_style)
+    }
+
+    fn compute_overflow(&self) -> Rect<Au> {
+        self.block_flow.compute_overflow()
+    }
+
+    fn generated_containing_block_size(&self, flow: OpaqueFlow) -> LogicalSize<Au> {
+        self.block_flow.generated_containing_block_size(flow)
+    }
+
+    fn iterate_through_fragment_border_boxes(&self,
+                                             iterator: &mut FragmentBorderBoxIterator,
+                                             level: i32,
+                                             stacking_context_position: &Point2D<Au>) {
+        self.block_flow.iterate_through_fragment_border_boxes(iterator, level, stacking_context_position);
+    }
+
+    fn mutate_fragments(&mut self, mutator: &mut FnMut(&mut Fragment)) {
+        self.block_flow.mutate_fragments(mutator);
+    }
+}

components/layout/flow.rs

@@ -517,6 +517,7 @@ pub enum FlowClass {
     TableCaption,
     TableCell,
     Multicol,
+    Flex,
 }
 
 /// A top-down traversal.
@@ -1173,6 +1174,8 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
             FlowClass::Table => !child.is_proper_table_child(),
             FlowClass::TableRowGroup => !child.is_table_row(),
             FlowClass::TableRow => !child.is_table_cell(),
+            // FIXME(zentner): According to spec, anonymous flex items are only needed for text.
+            FlowClass::Flex => child.is_inline_flow(),
             _ => false
         }
     }
@@ -1210,6 +1213,15 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
                 let hide = node.style().get_inheritedtable().empty_cells == empty_cells::T::hide;
                 Arc::new(TableCellFlow::from_node_fragment_and_visibility_flag(node, fragment, !hide))
             },
+            FlowClass::Flex => {
+                let fragment =
+                    Fragment::from_opaque_node_and_style(node.opaque(),
+                                                         PseudoElementType::Normal,
+                                                         style,
+                                                         node.restyle_damage(),
+                                                         SpecificFragmentInfo::Generic);
+                Arc::new(BlockFlow::from_fragment(fragment, None))
+            },
             _ => {
                 panic!("no need to generate a missing child")
             }

components/layout/lib.rs

@@ -72,6 +72,7 @@ pub mod construct;
 pub mod context;
 pub mod data;
 pub mod display_list_builder;
+pub mod flex;
 pub mod floats;
 pub mod flow;
 pub mod flow_list;

components/script/dom/webidls/CSSStyleDeclaration.webidl

@@ -204,4 +204,6 @@ partial interface CSSStyleDeclaration {
   [SetterThrows, TreatNullAs=EmptyString] attribute DOMString transitionTimingFunction;
   [SetterThrows, TreatNullAs=EmptyString] attribute DOMString transitionProperty;
   [SetterThrows, TreatNullAs=EmptyString] attribute DOMString transitionDelay;
+
+  [SetterThrows, TreatNullAs=EmptyString] attribute DOMString flexDirection;
 };

components/style/properties.mako.rs

@@ -407,15 +407,66 @@ pub mod longhands {
     ${new_style_struct("Box", is_inherited=False)}
 
     // TODO(SimonSapin): don't parse `inline-table`, since we don't support it
-    <%self:single_keyword_computed name="display"
-            custom_cascade="True"
-            values="inline block inline-block
+    <%self:longhand name="display" custom_cascade="True">
+        <%
+            values = """inline block inline-block
                 table inline-table table-row-group table-header-group table-footer-group
                 table-row table-column-group table-column table-cell table-caption
-            list-item
-            none">
+                list-item flex
+                none
+            """.split()
+            experimental_values = set("flex".split())
+        %>
+        pub use self::computed_value::T as SpecifiedValue;
         use values::computed::Context;
 
+        pub mod computed_value {
+            #[allow(non_camel_case_types)]
+            #[derive(Clone, Eq, PartialEq, Copy, Hash, RustcEncodable, Debug, HeapSizeOf)]
+            #[derive(Deserialize, Serialize)]
+            pub enum T {
+                % for value in values:
+                    ${to_rust_ident(value)},
+                % endfor
+            }
+
+            impl ::cssparser::ToCss for T {
+                fn to_css<W>(&self, dest: &mut W) -> ::std::fmt::Result
+                where W: ::std::fmt::Write {
+                    match self {
+                        % for value in values:
+                            &T::${to_rust_ident(value)} => dest.write_str("${value}"),
+                        % endfor
+                    }
+                }
+            }
+        }
+        #[inline] pub fn get_initial_value() -> computed_value::T {
+            computed_value::T::${to_rust_ident(values[0])}
+        }
+        pub fn parse(_context: &ParserContext, input: &mut Parser)
+                     -> Result<SpecifiedValue, ()> {
+            match_ignore_ascii_case! { try!(input.expect_ident()),
+                % for value in values[:-1]:
+                    "${value}" => {
+                        % if value in experimental_values:
+                            if !::util::opts::experimental_enabled() { return Err(()) }
+                        % endif
+                        Ok(computed_value::T::${to_rust_ident(value)})
+                    },
+                % endfor
+                % for value in values[-1:]:
+                    "${value}" => {
+                        % if value in experimental_values:
+                            if !::util::opts::experimental_enabled() { return Err(()) }
+                        % endif
+                        Ok(computed_value::T::${to_rust_ident(value)})
+                    }
+                % endfor
+                _ => Err(())
+            }
+        }
+
         impl ToComputedValue for SpecifiedValue {
             type ComputedValue = computed_value::T;
 
@@ -457,7 +508,7 @@ pub mod longhands {
                 longhands::_servo_text_decorations_in_effect::derive_from_display(*computed_value,
                                                                                   &context);
         }
-    </%self:single_keyword_computed>
+    </%self:longhand>
 
     ${single_keyword("position", "static absolute relative fixed")}
     ${single_keyword("float", "none left right")}
@@ -4746,6 +4797,14 @@ pub mod longhands {
         pub use properties::longhands::transition_duration::{get_initial_single_value};
         pub use properties::longhands::transition_duration::{get_initial_value, parse, parse_one};
     </%self:longhand>
+
+    // CSS Flexible Box Layout Module Level 1
+    // http://www.w3.org/TR/css3-flexbox/
+
+    ${new_style_struct("Flex", is_inherited=False)}
+
+    // Flex container properties
+    ${single_keyword("flex-direction", "row row-reverse column column-reverse", experimental=True)}
 }
 
 

tests/ref/basic.list

@@ -98,6 +98,8 @@ flaky_cpu == append_style_a.html append_style_b.html
 == first_child_pseudo_a.html first_child_pseudo_b.html
 == first_of_type_pseudo_a.html first_of_type_pseudo_b.html
 == fixed_width_overrides_child_intrinsic_width_a.html fixed_width_overrides_child_intrinsic_width_ref.html
+experimental == flex_column_direction.html flex_column_direction_ref.html
+experimental == flex_row_direction.html flex_row_direction_ref.html
 == float_clearance_a.html float_clearance_ref.html
 == float_clearance_intrinsic_width_a.html float_clearance_intrinsic_width_ref.html
 == float_intrinsic_height.html float_intrinsic_height_ref.html

tests/ref/flex_column_direction.html

@@ -0,0 +1,37 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>CSS Test: flex container should layout flex items horizontally</title>
+  <link rel="author" title="Kyle Zentner" href="mailto:zentner.kyle@gmail.com">
+  <link rel="help" href="https://drafts.csswg.org/css-flexbox/">
+  <style>
+    body {
+      margin: 0;
+    }
+    .flexbox {
+      display: flex;
+      flex-direction: column;
+      height: 300px;
+    }
+    .first-item {
+      background: orange;
+      height: 150px;
+      width: 100px;
+      flex: 1 0 auto;
+    }
+    .second-item {
+      background: blue;
+      height: 150px;
+      width: 100px;
+      flex: 1 0 auto;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexbox">
+    <div class="first-item"></div>
+    <div class="second-item"></div>
+  </div>
+</body>
+</html>

tests/ref/flex_column_direction_ref.html

@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>CSS Reftest Reference</title>
+  <link rel="author" title="Kyle Zentner" href="mailto:zentner.kyle@gmail.com">
+  <style>
+    body {
+      margin: 0;
+    }
+    .flexbox {
+      height: 300px;
+    }
+    .first-item {
+      background: orange;
+      width: 100px;
+      height: 150px;
+    }
+    .second-item {
+      background: blue;
+      width: 100px;
+      height: 150px;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexbox">
+    <div class="first-item"></div>
+    <div class="second-item"></div>
+  </div>
+</body>
+</html>

tests/ref/flex_row_direction.html

@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>CSS Test: flex container should layout flex items horizontally</title>
+  <link rel="author" title="Kyle Zentner" href="mailto:zentner.kyle@gmail.com">
+  <link rel="help" href="https://drafts.csswg.org/css-flexbox/">
+  <style>
+    body {
+      margin: 0;
+    }
+    .flexbox {
+      display: flex;
+      width: 300px;
+    }
+    .first-item {
+      background: orange;
+      height: 100px;
+      flex: 1 0 auto;
+    }
+    .second-item {
+      background: blue;
+      height: 100px;
+      flex: 1 0 auto;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexbox">
+    <div class="first-item"></div>
+    <div class="second-item"></div>
+  </div>
+</body>
+</html>

tests/ref/flex_row_direction_ref.html

@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>CSS Reftest Reference</title>
+  <link rel="author" title="Kyle Zentner" href="mailto:zentner.kyle@gmail.com">
+  <style>
+    body {
+      margin: 0;
+    }
+    .flexbox {
+      width: 300px;
+    }
+    .first-item {
+      background: orange;
+      height: 100px;
+      width: 150px;
+      float: left;
+    }
+    .second-item {
+      background: blue;
+      height: 100px;
+      width: 150px;
+      float: left;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexbox">
+    <div class="first-item"></div>
+    <div class="second-item"></div>
+  </div>
+</body>
+</html>