Auto merge of #26838 - servo:flexbox, r=nox

Flexbox, the boring parts

I have a local branch starting to implement https://drafts.csswg.org/css-flexbox/#layout-algorithm. It’s not PR-ready yet, but it’s going to be large so here are some of the less interesting parts meaningful by themselves. Landing the module split in particular will help reduce merge conflicts.

CC https://github.com/servo/servo/issues/26639

5 files changed, 71 insertions, 45 deletions

diff --git a/components/layout_2020/flexbox.rs b/components/layout_2020/flexbox/construct.rs
index 32ea3340ff7..e23858efe7f 100644
--- a/components/layout_2020/flexbox.rs
+++ b/components/layout_2020/flexbox/construct.rs
@@ -2,36 +2,21 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+use super::{FlexContainer, FlexLevelBox};
 use crate::cell::ArcRefCell;
 use crate::context::LayoutContext;
 use crate::dom_traversal::{
     BoxSlot, Contents, NodeAndStyleInfo, NodeExt, NonReplacedContents, TraversalHandler,
 };
 use crate::element_data::LayoutBox;
-use crate::formatting_contexts::{IndependentFormattingContext, IndependentLayout};
+use crate::formatting_contexts::IndependentFormattingContext;
 use crate::fragments::Tag;
-use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
+use crate::positioned::AbsolutelyPositionedBox;
 use crate::sizing::{BoxContentSizes, ContentSizes, ContentSizesRequest};
 use crate::style_ext::DisplayGeneratingBox;
-use crate::ContainingBlock;
 use rayon::iter::{IntoParallelIterator, ParallelIterator};
 use std::borrow::Cow;
-use style::values::computed::Length;
 use style::values::specified::text::TextDecorationLine;
-use style::Zero;
-
-// FIXME: `min-width: auto` is not zero: https://drafts.csswg.org/css-flexbox/#min-size-auto
-
-#[derive(Debug, Serialize)]
-pub(crate) struct FlexContainer {
-    children: Vec<ArcRefCell<FlexLevelBox>>,
-}
-
-#[derive(Debug, Serialize)]
-pub(crate) enum FlexLevelBox {
-    FlexItem(IndependentFormattingContext),
-    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
-}
 
 impl FlexContainer {
     pub fn construct<'dom>(
@@ -230,23 +215,3 @@ where
         FlexContainer { children }
     }
 }
-
-impl FlexContainer {
-    pub(crate) fn layout(
-        &self,
-        layout_context: &LayoutContext,
-        positioning_context: &mut PositioningContext,
-        containing_block: &ContainingBlock,
-        tree_rank: usize,
-    ) -> IndependentLayout {
-        // FIXME
-        let _ = layout_context;
-        let _ = positioning_context;
-        let _ = containing_block;
-        let _ = tree_rank;
-        IndependentLayout {
-            fragments: Vec::new(),
-            content_block_size: Length::zero(),
-        }
-    }
-}
diff --git a/components/layout_2020/flexbox/layout.rs b/components/layout_2020/flexbox/layout.rs
new file mode 100644
index 00000000000..1da062b7764
--- /dev/null
+++ b/components/layout_2020/flexbox/layout.rs
@@ -0,0 +1,33 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use super::FlexContainer;
+use crate::context::LayoutContext;
+use crate::formatting_contexts::IndependentLayout;
+use crate::positioned::PositioningContext;
+use crate::ContainingBlock;
+use style::values::computed::Length;
+use style::Zero;
+
+// FIXME: `min-width: auto` is not zero: https://drafts.csswg.org/css-flexbox/#min-size-auto
+
+impl FlexContainer {
+    pub(crate) fn layout(
+        &self,
+        layout_context: &LayoutContext,
+        positioning_context: &mut PositioningContext,
+        containing_block: &ContainingBlock,
+        tree_rank: usize,
+    ) -> IndependentLayout {
+        // FIXME
+        let _ = layout_context;
+        let _ = positioning_context;
+        let _ = containing_block;
+        let _ = tree_rank;
+        IndependentLayout {
+            fragments: Vec::new(),
+            content_block_size: Length::zero(),
+        }
+    }
+}
diff --git a/components/layout_2020/flexbox/mod.rs b/components/layout_2020/flexbox/mod.rs
new file mode 100644
index 00000000000..c7aed0bd0e9
--- /dev/null
+++ b/components/layout_2020/flexbox/mod.rs
@@ -0,0 +1,21 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::cell::ArcRefCell;
+use crate::formatting_contexts::IndependentFormattingContext;
+use crate::positioned::AbsolutelyPositionedBox;
+
+mod construct;
+mod layout;
+
+#[derive(Debug, Serialize)]
+pub(crate) struct FlexContainer {
+    children: Vec<ArcRefCell<FlexLevelBox>>,
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) enum FlexLevelBox {
+    FlexItem(IndependentFormattingContext),
+    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
+}
diff --git a/components/style/properties/longhands/position.mako.rs b/components/style/properties/longhands/position.mako.rs
index 239c2edd5cb..25354ab19af 100644
--- a/components/style/properties/longhands/position.mako.rs
+++ b/components/style/properties/longhands/position.mako.rs
@@ -72,7 +72,8 @@ ${helpers.predefined_type(
 ${helpers.single_keyword(
     "flex-direction",
     "row row-reverse column column-reverse",
-    engines="gecko servo-2013",
+    engines="gecko servo-2013 servo-2020",
+    servo_2020_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-direction-property",
     extra_prefixes="webkit",
     animation_value_type="discrete",
@@ -83,7 +84,8 @@ ${helpers.single_keyword(
 ${helpers.single_keyword(
     "flex-wrap",
     "nowrap wrap wrap-reverse",
-    engines="gecko servo-2013",
+    engines="gecko servo-2013 servo-2020",
+    servo_2020_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-wrap-property",
     extra_prefixes="webkit",
     animation_value_type="discrete",
@@ -205,7 +207,8 @@ ${helpers.predefined_type(
     "flex-grow",
     "NonNegativeNumber",
     "From::from(0.0)",
-    engines="gecko servo-2013",
+    engines="gecko servo-2013 servo-2020",
+    servo_2020_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-grow-property",
     extra_prefixes="webkit",
     animation_value_type="NonNegativeNumber",
@@ -216,7 +219,8 @@ ${helpers.predefined_type(
     "flex-shrink",
     "NonNegativeNumber",
     "From::from(1.0)",
-    engines="gecko servo-2013",
+    engines="gecko servo-2013 servo-2020",
+    servo_2020_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-shrink-property",
     extra_prefixes="webkit",
     animation_value_type="NonNegativeNumber",
@@ -278,7 +282,8 @@ ${helpers.predefined_type(
     "flex-basis",
     "FlexBasis",
     "computed::FlexBasis::auto()",
-    engines="gecko servo-2013",
+    engines="gecko servo-2013 servo-2020",
+    servo_2020_pref="layout.flexbox.enabled",
     spec="https://drafts.csswg.org/css-flexbox/#flex-basis-property",
     extra_prefixes="webkit",
     animation_value_type="FlexBasis",
diff --git a/components/style/properties/shorthands/position.mako.rs b/components/style/properties/shorthands/position.mako.rs
index 48e56e6ef3c..ff9b5cd5790 100644
--- a/components/style/properties/shorthands/position.mako.rs
+++ b/components/style/properties/shorthands/position.mako.rs
@@ -5,7 +5,8 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="flex-flow"
-                    engines="gecko servo-2013"
+                    engines="gecko servo-2013 servo-2020",
+                    servo_2020_pref="layout.flexbox.enabled",
                     sub_properties="flex-direction flex-wrap"
                     extra_prefixes="webkit"
                     derive_serialize="True"
@@ -45,7 +46,8 @@
 </%helpers:shorthand>
 
 <%helpers:shorthand name="flex"
-                    engines="gecko servo-2013"
+                    engines="gecko servo-2013 servo-2020",
+                    servo_2020_pref="layout.flexbox.enabled",
                     sub_properties="flex-grow flex-shrink flex-basis"
                     extra_prefixes="webkit"
                     derive_serialize="True"