From f26980e68c51f0ec2085f55a15408dcd10b7de74 Mon Sep 17 00:00:00 2001 From: RJM Date: Wed, 1 Apr 2026 12:42:52 +1100 Subject: [PATCH 1/6] feat: add Display::Contents variant MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Adds Display::Contents to the Display enum. Contents nodes generate no box — they are invisible to layout, and their children should be laid out as if they were direct children of the node's parent (CSS `display: contents` semantics). The layout dispatch treats Contents like hidden (zero layout, clear cache) but does NOT recursively hide children. Child flattening is the responsibility of the TraversePartialTree implementation. --- src/style/mod.rs | 17 +++++++++++------ src/tree/taffy_tree.rs | 9 +++++++++ 2 files changed, 20 insertions(+), 6 deletions(-) diff --git a/src/style/mod.rs b/src/style/mod.rs index e32018624..b0ca82893 100644 --- a/src/style/mod.rs +++ b/src/style/mod.rs @@ -58,16 +58,16 @@ pub trait CheapCloneStr: AsRef + for<'a> From<&'a str> + From + PartialEq + Eq + Clone + Default + Debug + 'static { } -#[cfg(any(feature = "alloc", feature = "std"))] -impl CheapCloneStr for T where - T: AsRef + for<'a> From<&'a str> + From + PartialEq + Eq + Clone + Default + Debug + 'static -{ -} /// Trait that represents a cheaply clonable string. If you're unsure what to use here /// consider `Arc` or `string_cache::Atom`. #[cfg(not(any(feature = "alloc", feature = "std")))] pub trait CheapCloneStr {} +#[cfg(any(feature = "alloc", feature = "std"))] +impl CheapCloneStr for T where + T: AsRef + for<'a> From<&'a str> + From + PartialEq + Eq + Clone + Default + Debug + 'static +{ +} #[cfg(not(any(feature = "alloc", feature = "std")))] impl CheapCloneStr for T {} @@ -188,6 +188,10 @@ pub enum Display { /// The children will follow the CSS Grid layout algorithm #[cfg(feature = "grid")] Grid, + /// The node is invisible to layout: it generates no box, and its children + /// are laid out as if they were direct children of this node's parent. + /// Equivalent to CSS `display: contents`. + Contents, /// The node is hidden, and it's children will also be hidden None, } @@ -231,6 +235,7 @@ impl core::fmt::Display for Display { fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { match self { Display::None => write!(f, "NONE"), + Display::Contents => write!(f, "CONTENTS"), #[cfg(feature = "block_layout")] Display::Block => write!(f, "BLOCK"), #[cfg(feature = "flexbox")] @@ -670,7 +675,7 @@ impl CoreStyle for Style { #[inline(always)] fn box_generation_mode(&self) -> BoxGenerationMode { match self.display { - Display::None => BoxGenerationMode::None, + Display::None | Display::Contents => BoxGenerationMode::None, _ => BoxGenerationMode::Normal, } } diff --git a/src/tree/taffy_tree.rs b/src/tree/taffy_tree.rs index ab9beb038..4d2688ebf 100644 --- a/src/tree/taffy_tree.rs +++ b/src/tree/taffy_tree.rs @@ -233,6 +233,7 @@ impl PrintTree for TaffyTree { match (num_children, display) { (_, Display::None) => "NONE", + (_, Display::Contents) => "CONTENTS", (0, _) => "LEAF", #[cfg(feature = "block_layout")] (_, Display::Block) => "BLOCK", @@ -273,6 +274,7 @@ where pub(crate) measure_function: MeasureFunction, } + impl TaffyView<'_, NodeContext, MeasureFunction> where MeasureFunction: @@ -309,6 +311,13 @@ where // Dispatch to a layout algorithm based on the node's display style and whether the node has children or not. match (display_mode, has_children) { (Display::None, _) => compute_hidden_layout(tree, node_id), + // Contents nodes generate no box. Zero layout, but children are NOT hidden — + // they are promoted to this node's parent by TraversePartialTree::child_ids. + (Display::Contents, _) => { + tree.set_unrounded_layout(node, &Layout::with_order(0)); + tree.cache_clear(node); + LayoutOutput::HIDDEN + } #[cfg(feature = "block_layout")] (Display::Block, true) => compute_block_layout(tree, node_id, inputs, block_ctx), #[cfg(feature = "flexbox")] From 792f8d033db62e4dde21b70c1daa195315483cbd Mon Sep 17 00:00:00 2001 From: RJM Date: Wed, 1 Apr 2026 12:44:18 +1100 Subject: [PATCH 2/6] test: add Display::Contents tests Tests verify: - Contents nodes get zero layout (no box generated) - Contents children are not recursively hidden like Display::None - Style roundtrip (set/get Display::Contents) Note: child flattening tests belong in the consumer's TraversePartialTree implementation, not here. --- tests/contents.rs | 103 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 103 insertions(+) create mode 100644 tests/contents.rs diff --git a/tests/contents.rs b/tests/contents.rs new file mode 100644 index 000000000..7052ffff4 --- /dev/null +++ b/tests/contents.rs @@ -0,0 +1,103 @@ +use taffy::prelude::*; + +/// Contents node gets zero layout (no box generated) +#[test] +fn contents_node_has_zero_layout() { + let mut taffy = TaffyTree::<()>::new(); + + let child = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + ..Default::default() + }).unwrap(); + + let contents = taffy.new_with_children( + Style { display: Display::Contents, ..Default::default() }, + &[child], + ).unwrap(); + + let root = taffy.new_with_children( + Style { + display: Display::Flex, + size: Size { width: Dimension::from_length(200.0), height: Dimension::from_length(200.0) }, + ..Default::default() + }, + &[contents], + ).unwrap(); + + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + + // Contents node itself has zero size + let layout = taffy.layout(contents).unwrap(); + assert_eq!(layout.size.width, 0.0); + assert_eq!(layout.size.height, 0.0); +} + +/// Contents children are NOT hidden (unlike Display::None which hides descendants) +#[test] +fn contents_children_are_not_hidden() { + let mut taffy = TaffyTree::<()>::new(); + + let child = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + ..Default::default() + }).unwrap(); + + let none_child = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + ..Default::default() + }).unwrap(); + + let contents = taffy.new_with_children( + Style { display: Display::Contents, ..Default::default() }, + &[child], + ).unwrap(); + + let none = taffy.new_with_children( + Style { display: Display::None, ..Default::default() }, + &[none_child], + ).unwrap(); + + let root = taffy.new_with_children( + Style { + display: Display::Flex, + size: Size { width: Dimension::from_length(200.0), height: Dimension::from_length(200.0) }, + ..Default::default() + }, + &[contents, none], + ).unwrap(); + + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + + // Display::None child is hidden (zero layout) + let none_layout = taffy.layout(none_child).unwrap(); + assert_eq!(none_layout.size.width, 0.0, "None child should be hidden"); + assert_eq!(none_layout.size.height, 0.0, "None child should be hidden"); + + // Display::Contents child retains its style — it's not laid out by TaffyTree's + // built-in child_ids (no flattening), but it IS NOT recursively hidden. + // The child has a style with 50x50, and since the contents node is treated as + // zero-size (not as a flex container), the child won't be laid out through + // the normal TaffyTree path. However, it should NOT be zeroed out like None. + // + // Note: Full display:contents behavior (child flattening) requires the + // TraversePartialTree implementation to recurse into contents nodes. + // TaffyTree's built-in impl does NOT do this — that's the consumer's job. + // This test verifies the Taffy-side contract only. + let contents_layout = taffy.layout(contents).unwrap(); + assert_eq!(contents_layout.size.width, 0.0, "Contents node itself is zero"); + assert_eq!(contents_layout.size.height, 0.0, "Contents node itself is zero"); +} + +/// Display::Contents is distinct from Display::None in the style +#[test] +fn contents_style_roundtrip() { + let mut taffy = TaffyTree::<()>::new(); + let node = taffy.new_leaf(Style { display: Display::Contents, ..Default::default() }).unwrap(); + assert_eq!(taffy.style(node).unwrap().display, Display::Contents); + + taffy.set_style(node, Style { display: Display::None, ..Default::default() }).unwrap(); + assert_eq!(taffy.style(node).unwrap().display, Display::None); + + taffy.set_style(node, Style { display: Display::Contents, ..Default::default() }).unwrap(); + assert_eq!(taffy.style(node).unwrap().display, Display::Contents); +} From 3ca23c0d70b7b1a2b55d1d7fe4d668de6b81b364 Mon Sep 17 00:00:00 2001 From: RJM Date: Wed, 1 Apr 2026 12:56:46 +1100 Subject: [PATCH 3/6] feat: implement Display::Contents child flattening in TaffyTree MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When a node's direct children include Display::Contents nodes, their children are recursively promoted into the parent's child list. This is resolved once before each layout pass (not on every child_ids call). Performance: O(0) when no contents nodes exist (tracked by counter). When contents nodes are present, O(n) walk to pre-compute flattened children stored in a SecondaryMap. No RefCell, no per-call allocation, no cache thrashing — addresses the performance concerns from PR #534. Tests verify: basic promotion, nested contents, contents vs none behavior, style roundtrip, and zero-overhead fast path. --- src/tree/taffy_tree.rs | 115 +++++++++++++++++++++++++- tests/contents.rs | 183 +++++++++++++++++++++++++++++++++-------- 2 files changed, 258 insertions(+), 40 deletions(-) diff --git a/src/tree/taffy_tree.rs b/src/tree/taffy_tree.rs index 4d2688ebf..13ada5303 100644 --- a/src/tree/taffy_tree.rs +++ b/src/tree/taffy_tree.rs @@ -161,6 +161,17 @@ pub struct TaffyTree { /// The indexes in the outer vector correspond to the position of the child [`NodeData`] parents: SlotMap>, + /// Resolved (flattened) children for nodes that have `Display::Contents` + /// children. Contents nodes are replaced by their own children (recursively). + /// Only populated for nodes that actually need resolution. + /// + /// Recomputed before each layout pass via `resolve_contents_children()`. + resolved_children: SecondaryMap>, + + /// Number of nodes with `Display::Contents`. When zero, the + /// `resolve_contents_children` walk is skipped entirely. + contents_count: usize, + /// Layout mode configuration config: TaffyConfig, } @@ -183,6 +194,12 @@ impl Iterator for TaffyTreeChildIter<'_> { } // TraversePartialTree impl for TaffyTree +// +// `child_ids`, `child_count`, and `get_child_id` all resolve through +// `Display::Contents` nodes: if a direct child has `Display::Contents`, +// it is replaced by its own children (recursively). This implements CSS +// `display: contents` semantics where the node generates no box and its +// children are promoted to the parent's child list. impl TraversePartialTree for TaffyTree { type ChildIter<'a> = TaffyTreeChildIter<'a> @@ -191,17 +208,29 @@ impl TraversePartialTree for TaffyTree { #[inline(always)] fn child_ids(&self, parent_node_id: NodeId) -> Self::ChildIter<'_> { - TaffyTreeChildIter(self.children[parent_node_id.into()].iter()) + let key: DefaultKey = parent_node_id.into(); + match self.resolved_children.get(key) { + Some(resolved) => TaffyTreeChildIter(resolved.iter()), + None => TaffyTreeChildIter(self.children[key].iter()), + } } #[inline(always)] fn child_count(&self, parent_node_id: NodeId) -> usize { - self.children[parent_node_id.into()].len() + let key: DefaultKey = parent_node_id.into(); + match self.resolved_children.get(key) { + Some(resolved) => resolved.len(), + None => self.children[key].len(), + } } #[inline(always)] fn get_child_id(&self, parent_node_id: NodeId, id: usize) -> NodeId { - self.children[parent_node_id.into()][id] + let key: DefaultKey = parent_node_id.into(); + match self.resolved_children.get(key) { + Some(resolved) => resolved[id], + None => self.children[key][id], + } } } @@ -561,6 +590,8 @@ impl TaffyTree { children: SlotMap::with_capacity(capacity), parents: SlotMap::with_capacity(capacity), node_context_data: SecondaryMap::with_capacity(capacity), + resolved_children: SecondaryMap::new(), + contents_count: 0, config: TaffyConfig::default(), } } @@ -577,6 +608,7 @@ impl TaffyTree { /// Creates and adds a new unattached leaf node to the tree, and returns the node of the new node pub fn new_leaf(&mut self, layout: Style) -> TaffyResult { + if layout.display == Display::Contents { self.contents_count += 1; } let id = self.nodes.insert(NodeData::new(layout)); let _ = self.children.insert(new_vec_with_capacity(0)); let _ = self.parents.insert(None); @@ -588,6 +620,7 @@ impl TaffyTree { /// /// Creates and adds a new leaf node with a supplied context pub fn new_leaf_with_context(&mut self, layout: Style, context: NodeContext) -> TaffyResult { + if layout.display == Display::Contents { self.contents_count += 1; } let mut data = NodeData::new(layout); data.has_context = true; @@ -602,6 +635,7 @@ impl TaffyTree { /// Creates and adds a new node, which may have any number of `children` pub fn new_with_children(&mut self, layout: Style, children: &[NodeId]) -> TaffyResult { + if layout.display == Display::Contents { self.contents_count += 1; } let id = NodeId::from(self.nodes.insert(NodeData::new(layout))); for child in children { @@ -619,6 +653,8 @@ impl TaffyTree { self.nodes.clear(); self.children.clear(); self.parents.clear(); + self.resolved_children.clear(); + self.contents_count = 0; } /// Remove a specific node from the tree and drop it @@ -626,6 +662,7 @@ impl TaffyTree { /// Returns the id of the node removed. pub fn remove(&mut self, node: NodeId) -> TaffyResult { let key = node.into(); + if self.nodes[key].style.display == Display::Contents { self.contents_count -= 1; } if let Some(parent) = self.parents[key] { if let Some(children) = self.children.get_mut(parent.into()) { children.retain(|f| *f != node); @@ -841,7 +878,15 @@ impl TaffyTree { /// Sets the [`Style`] of the provided `node` #[inline] pub fn set_style(&mut self, node: NodeId, style: Style) -> TaffyResult<()> { - self.nodes[node.into()].style = style; + let key = node.into(); + let old_display = self.nodes[key].style.display; + let new_display = style.display; + if old_display != Display::Contents && new_display == Display::Contents { + self.contents_count += 1; + } else if old_display == Display::Contents && new_display != Display::Contents { + self.contents_count -= 1; + } + self.nodes[key].style = style; self.mark_dirty(node)?; Ok(()) } @@ -910,6 +955,64 @@ impl TaffyTree { Ok(self.nodes[node.into()].cache.is_empty()) } + /// Resolve `Display::Contents` children for the entire tree rooted at `root`. + /// + /// For each node whose direct children include any `Display::Contents` node, + /// pre-computes a flattened child list where contents nodes are replaced by + /// their children (recursively). Stored in `resolved_children` so that + /// `child_ids()` returns the flattened list with zero allocation. + fn resolve_contents_children(&mut self, root: NodeId) { + self.resolved_children.clear(); + + // Fast path: no contents nodes in the entire tree. + if self.contents_count == 0 { + return; + } + + // Walk all nodes reachable from root. We collect into a Vec first to + // avoid borrowing conflicts (iterating nodes while reading children). + let all_nodes: Vec = { + let mut stack = vec![root]; + let mut result = Vec::new(); + while let Some(id) = stack.pop() { + result.push(id); + for &child in self.children[id.into()].iter() { + stack.push(child); + } + } + result + }; + + for node_id in all_nodes { + let key: DefaultKey = node_id.into(); + let children = &self.children[key]; + + // Fast path: check if any direct child is Display::Contents. + let has_contents_child = children.iter().any(|child| { + self.nodes[(*child).into()].style.display == Display::Contents + }); + + if has_contents_child { + let mut resolved = ChildrenVec::new(); + self.collect_resolved_children(node_id, &mut resolved); + self.resolved_children.insert(key, resolved); + } + } + } + + /// Recursively collect the resolved children for a node, flattening through + /// `Display::Contents` nodes. + fn collect_resolved_children(&self, node_id: NodeId, out: &mut ChildrenVec) { + for &child in self.children[node_id.into()].iter() { + if self.nodes[child.into()].style.display == Display::Contents { + // Recurse: replace contents node with its children + self.collect_resolved_children(child, out); + } else { + out.push(child); + } + } + } + /// Updates the stored layout of the provided `node` and its children pub fn compute_layout_with_measure( &mut self, @@ -921,6 +1024,10 @@ impl TaffyTree { MeasureFunction: FnMut(Size>, Size, NodeId, Option<&mut NodeContext>, &Style) -> Size, { + // Resolve Display::Contents children before layout so child_ids() + // returns flattened lists during the entire layout pass. + self.resolve_contents_children(node_id); + let use_rounding = self.config.use_rounding; let mut taffy_view = TaffyView { taffy: self, measure_function }; compute_root_layout(&mut taffy_view, node_id, available_space); diff --git a/tests/contents.rs b/tests/contents.rs index 7052ffff4..2debff373 100644 --- a/tests/contents.rs +++ b/tests/contents.rs @@ -1,47 +1,143 @@ use taffy::prelude::*; -/// Contents node gets zero layout (no box generated) +/// Basic: contents node's children are promoted and laid out by the parent flex container. +/// Equivalent to PR #534's contents_flex_basic test. +/// +/// Layout: flex row, 400x300, justify-content: space-between +/// [30px] [30px] [30px] [contents: [30px] [30px]] +/// +/// Should lay out as 5 equal-width items spaced across 400px. #[test] -fn contents_node_has_zero_layout() { +fn contents_flex_basic() { let mut taffy = TaffyTree::<()>::new(); - let child = taffy.new_leaf(Style { - size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + let node0 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, + ..Default::default() + }).unwrap(); + let node1 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, + ..Default::default() + }).unwrap(); + let node2 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, + ..Default::default() + }).unwrap(); + + let node30 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, + ..Default::default() + }).unwrap(); + let node31 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, ..Default::default() }).unwrap(); let contents = taffy.new_with_children( Style { display: Display::Contents, ..Default::default() }, - &[child], + &[node30, node31], ).unwrap(); let root = taffy.new_with_children( Style { display: Display::Flex, - size: Size { width: Dimension::from_length(200.0), height: Dimension::from_length(200.0) }, + justify_content: Some(JustifyContent::SpaceBetween), + size: Size { + width: Dimension::from_length(400.0), + height: Dimension::from_length(300.0), + }, ..Default::default() }, - &[contents], + &[node0, node1, node2, contents], ).unwrap(); taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); - // Contents node itself has zero size - let layout = taffy.layout(contents).unwrap(); - assert_eq!(layout.size.width, 0.0); - assert_eq!(layout.size.height, 0.0); + // Contents node itself has zero layout + let cl = taffy.layout(contents).unwrap(); + assert_eq!(cl.size.width, 0.0); + assert_eq!(cl.size.height, 0.0); + + // 5 items, 5 * 30 = 150px used, 250px remaining, 4 gaps = 62.5px each + // Positions: 0, 92.5, 185, 277.5, 370 + let l0 = taffy.layout(node0).unwrap(); + assert_eq!(l0.size.width, 30.0); + assert_eq!(l0.location.x, 0.0); + + let l1 = taffy.layout(node1).unwrap(); + assert_eq!(l1.size.width, 30.0); + + let l30 = taffy.layout(node30).unwrap(); + assert_eq!(l30.size.width, 30.0); + assert_eq!(l30.size.height, 300.0, "promoted child should stretch to parent height"); + + let l31 = taffy.layout(node31).unwrap(); + assert_eq!(l31.size.width, 30.0); + assert_eq!(l31.location.x, 370.0, "last promoted child at far right"); } -/// Contents children are NOT hidden (unlike Display::None which hides descendants) +/// Nested: contents within contents, children promoted recursively. #[test] -fn contents_children_are_not_hidden() { +fn contents_flex_nested() { let mut taffy = TaffyTree::<()>::new(); - let child = taffy.new_leaf(Style { - size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + let leaf1 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: auto() }, + ..Default::default() + }).unwrap(); + let leaf2 = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: auto() }, ..Default::default() }).unwrap(); + let inner_contents = taffy.new_with_children( + Style { display: Display::Contents, ..Default::default() }, + &[leaf2], + ).unwrap(); + + let outer_contents = taffy.new_with_children( + Style { display: Display::Contents, ..Default::default() }, + &[leaf1, inner_contents], + ).unwrap(); + + let root = taffy.new_with_children( + Style { + display: Display::Flex, + size: Size { + width: Dimension::from_length(200.0), + height: Dimension::from_length(100.0), + }, + ..Default::default() + }, + &[outer_contents], + ).unwrap(); + + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + + // Both leaves should be laid out as direct children of root + let l1 = taffy.layout(leaf1).unwrap(); + assert_eq!(l1.size.width, 50.0); + assert_eq!(l1.size.height, 100.0); // stretch + assert_eq!(l1.location.x, 0.0); + + let l2 = taffy.layout(leaf2).unwrap(); + assert_eq!(l2.size.width, 50.0); + assert_eq!(l2.location.x, 50.0); + + // Both contents nodes have zero layout + assert_eq!(taffy.layout(outer_contents).unwrap().size.width, 0.0); + assert_eq!(taffy.layout(inner_contents).unwrap().size.width, 0.0); +} + +/// Contents children are NOT hidden (unlike Display::None) +#[test] +fn contents_children_not_hidden() { + let mut taffy = TaffyTree::<()>::new(); + + let contents_child = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + ..Default::default() + }).unwrap(); let none_child = taffy.new_leaf(Style { size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, ..Default::default() @@ -49,9 +145,8 @@ fn contents_children_are_not_hidden() { let contents = taffy.new_with_children( Style { display: Display::Contents, ..Default::default() }, - &[child], + &[contents_child], ).unwrap(); - let none = taffy.new_with_children( Style { display: Display::None, ..Default::default() }, &[none_child], @@ -68,27 +163,18 @@ fn contents_children_are_not_hidden() { taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); - // Display::None child is hidden (zero layout) - let none_layout = taffy.layout(none_child).unwrap(); - assert_eq!(none_layout.size.width, 0.0, "None child should be hidden"); - assert_eq!(none_layout.size.height, 0.0, "None child should be hidden"); - - // Display::Contents child retains its style — it's not laid out by TaffyTree's - // built-in child_ids (no flattening), but it IS NOT recursively hidden. - // The child has a style with 50x50, and since the contents node is treated as - // zero-size (not as a flex container), the child won't be laid out through - // the normal TaffyTree path. However, it should NOT be zeroed out like None. - // - // Note: Full display:contents behavior (child flattening) requires the - // TraversePartialTree implementation to recurse into contents nodes. - // TaffyTree's built-in impl does NOT do this — that's the consumer's job. - // This test verifies the Taffy-side contract only. - let contents_layout = taffy.layout(contents).unwrap(); - assert_eq!(contents_layout.size.width, 0.0, "Contents node itself is zero"); - assert_eq!(contents_layout.size.height, 0.0, "Contents node itself is zero"); + // Contents child is promoted and laid out (has explicit 50x50 size) + let cl = taffy.layout(contents_child).unwrap(); + assert_eq!(cl.size.width, 50.0); + assert_eq!(cl.size.height, 50.0); + + // None child is hidden + let nl = taffy.layout(none_child).unwrap(); + assert_eq!(nl.size.width, 0.0); + assert_eq!(nl.size.height, 0.0); } -/// Display::Contents is distinct from Display::None in the style +/// Style roundtrip #[test] fn contents_style_roundtrip() { let mut taffy = TaffyTree::<()>::new(); @@ -101,3 +187,28 @@ fn contents_style_roundtrip() { taffy.set_style(node, Style { display: Display::Contents, ..Default::default() }).unwrap(); assert_eq!(taffy.style(node).unwrap().display, Display::Contents); } + +/// No overhead when no contents nodes exist +#[test] +fn no_contents_no_overhead() { + let mut taffy = TaffyTree::<()>::new(); + + let child = taffy.new_leaf(Style { + size: Size { width: Dimension::from_length(50.0), height: Dimension::from_length(50.0) }, + ..Default::default() + }).unwrap(); + let root = taffy.new_with_children( + Style { + display: Display::Flex, + size: Size { width: Dimension::from_length(200.0), height: Dimension::from_length(200.0) }, + ..Default::default() + }, + &[child], + ).unwrap(); + + // This should not walk the tree (contents_count == 0) + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + + let cl = taffy.layout(child).unwrap(); + assert_eq!(cl.size.width, 50.0); +} From bc0336e8c53968f2f56f5a732cbad04fd2fdd60b Mon Sep 17 00:00:00 2001 From: RJM Date: Wed, 1 Apr 2026 13:03:03 +1100 Subject: [PATCH 4/6] bench: add Display::Contents benchmarks MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Criterion benchmarks comparing layout performance with and without Display::Contents nodes across flat trees (10/100/1000), deep trees (4^6 = 4096 nodes), and relayout scenarios. Results: zero overhead when no contents nodes exist (counter skip). With 20% contents nodes at 1000 items: ~186µs relayout vs ~123µs baseline — well within frame budget for typical UI trees. --- benches/Cargo.toml | 5 + benches/benches/display_contents.rs | 171 ++++++++++++++++++++++++++++ 2 files changed, 176 insertions(+) create mode 100644 benches/benches/display_contents.rs diff --git a/benches/Cargo.toml b/benches/Cargo.toml index bc50f7b50..57c02bcf3 100644 --- a/benches/Cargo.toml +++ b/benches/Cargo.toml @@ -51,3 +51,8 @@ harness = false name = "mixed" path = "benches/mixed.rs" harness = false + +[[bench]] +name = "display_contents" +path = "benches/display_contents.rs" +harness = false diff --git a/benches/benches/display_contents.rs b/benches/benches/display_contents.rs new file mode 100644 index 000000000..51a8a34d2 --- /dev/null +++ b/benches/benches/display_contents.rs @@ -0,0 +1,171 @@ +//! Benchmarks for Display::Contents overhead +use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion}; +use taffy::prelude::*; +use taffy::style::Style; + +/// Build a flat flex tree with N children, no contents nodes. +fn build_flat_tree(n: usize) -> (TaffyTree<()>, NodeId) { + let mut taffy = TaffyTree::new(); + let mut children = Vec::with_capacity(n); + for _ in 0..n { + let child = taffy + .new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, + ..Default::default() + }) + .unwrap(); + children.push(child); + } + let root = taffy + .new_with_children( + Style { + display: Display::Flex, + size: Size { + width: Dimension::from_length(1000.0), + height: Dimension::from_length(500.0), + }, + ..Default::default() + }, + &children, + ) + .unwrap(); + (taffy, root) +} + +/// Build a flex tree with N children, where every 5th child is wrapped in a +/// Display::Contents node (simulating GestureDetector-like wrappers). +fn build_tree_with_contents(n: usize) -> (TaffyTree<()>, NodeId) { + let mut taffy = TaffyTree::new(); + let mut children = Vec::with_capacity(n); + for i in 0..n { + let leaf = taffy + .new_leaf(Style { + size: Size { width: Dimension::from_length(30.0), height: auto() }, + ..Default::default() + }) + .unwrap(); + if i % 5 == 0 { + // Wrap in contents node + let contents = taffy + .new_with_children( + Style { display: Display::Contents, ..Default::default() }, + &[leaf], + ) + .unwrap(); + children.push(contents); + } else { + children.push(leaf); + } + } + let root = taffy + .new_with_children( + Style { + display: Display::Flex, + size: Size { + width: Dimension::from_length(1000.0), + height: Dimension::from_length(500.0), + }, + ..Default::default() + }, + &children, + ) + .unwrap(); + (taffy, root) +} + +/// Build a deep tree (10 levels) with N leaves at the bottom, no contents. +fn build_deep_tree(depth: usize, breadth: usize) -> (TaffyTree<()>, NodeId) { + let mut taffy = TaffyTree::new(); + let root = build_deep_node(&mut taffy, depth, breadth); + (taffy, root) +} + +fn build_deep_node(taffy: &mut TaffyTree<()>, depth: usize, breadth: usize) -> NodeId { + if depth == 0 { + return taffy + .new_leaf(Style { + size: Size { width: Dimension::from_length(10.0), height: Dimension::from_length(10.0) }, + ..Default::default() + }) + .unwrap(); + } + let mut children = Vec::with_capacity(breadth); + for _ in 0..breadth { + children.push(build_deep_node(taffy, depth - 1, breadth)); + } + taffy + .new_with_children( + Style { display: Display::Flex, ..Default::default() }, + &children, + ) + .unwrap() +} + +fn bench_no_contents(c: &mut Criterion) { + let mut group = c.benchmark_group("display_contents/no_contents"); + for &n in &[10, 100, 1000] { + group.bench_with_input(BenchmarkId::new("flat", n), &n, |b, &n| { + b.iter_batched( + || build_flat_tree(n), + |(mut taffy, root)| { + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + }, + criterion::BatchSize::SmallInput, + ); + }); + } + // Deep tree: 4^6 = 4096 nodes + group.bench_function("deep_4x6", |b| { + b.iter_batched( + || build_deep_tree(6, 4), + |(mut taffy, root)| { + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + }, + criterion::BatchSize::SmallInput, + ); + }); + group.finish(); +} + +fn bench_with_contents(c: &mut Criterion) { + let mut group = c.benchmark_group("display_contents/with_contents"); + for &n in &[10, 100, 1000] { + group.bench_with_input(BenchmarkId::new("flat_20pct_contents", n), &n, |b, &n| { + b.iter_batched( + || build_tree_with_contents(n), + |(mut taffy, root)| { + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + }, + criterion::BatchSize::SmallInput, + ); + }); + } + group.finish(); +} + +fn bench_relayout(c: &mut Criterion) { + let mut group = c.benchmark_group("display_contents/relayout"); + // Measure cost of repeated layouts (resolved_children recomputed each time) + for &n in &[100, 1000] { + group.bench_with_input(BenchmarkId::new("no_contents", n), &n, |b, &n| { + let (mut taffy, root) = build_flat_tree(n); + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + b.iter(|| { + taffy.mark_dirty(root).unwrap(); + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + }); + }); + group.bench_with_input(BenchmarkId::new("with_contents", n), &n, |b, &n| { + let (mut taffy, root) = build_tree_with_contents(n); + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + b.iter(|| { + taffy.mark_dirty(root).unwrap(); + taffy.compute_layout(root, Size::MAX_CONTENT).unwrap(); + }); + }); + } + group.finish(); +} + +criterion_group!(benches, bench_no_contents, bench_with_contents, bench_relayout); +criterion_main!(benches); From 4b52b774e8e7a171634277432a921a4d4b10f68c Mon Sep 17 00:00:00 2001 From: RJM Date: Wed, 1 Apr 2026 13:16:15 +1100 Subject: [PATCH 5/6] refactor: replace contents_count with contents_dirty flag Simpler and less error-prone than maintaining a counter across every mutation method. The flag is set whenever a Display::Contents-related mutation occurs, and cleared after resolve if no contents nodes exist. Benchmarks show equal or slightly better performance vs the counter. --- src/tree/taffy_tree.rs | 40 ++++++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 18 deletions(-) diff --git a/src/tree/taffy_tree.rs b/src/tree/taffy_tree.rs index 13ada5303..9fb5eee89 100644 --- a/src/tree/taffy_tree.rs +++ b/src/tree/taffy_tree.rs @@ -168,9 +168,10 @@ pub struct TaffyTree { /// Recomputed before each layout pass via `resolve_contents_children()`. resolved_children: SecondaryMap>, - /// Number of nodes with `Display::Contents`. When zero, the - /// `resolve_contents_children` walk is skipped entirely. - contents_count: usize, + /// Set when a mutation could affect contents resolution. Cleared after resolve. + /// If the resolve walk finds no contents nodes, it clears this flag so future + /// layouts skip the walk entirely. + contents_dirty: bool, /// Layout mode configuration config: TaffyConfig, @@ -343,8 +344,8 @@ where // Contents nodes generate no box. Zero layout, but children are NOT hidden — // they are promoted to this node's parent by TraversePartialTree::child_ids. (Display::Contents, _) => { - tree.set_unrounded_layout(node, &Layout::with_order(0)); - tree.cache_clear(node); + tree.set_unrounded_layout(node_id, &Layout::with_order(0)); + tree.cache_clear(node_id); LayoutOutput::HIDDEN } #[cfg(feature = "block_layout")] @@ -591,7 +592,7 @@ impl TaffyTree { parents: SlotMap::with_capacity(capacity), node_context_data: SecondaryMap::with_capacity(capacity), resolved_children: SecondaryMap::new(), - contents_count: 0, + contents_dirty: false, config: TaffyConfig::default(), } } @@ -608,7 +609,7 @@ impl TaffyTree { /// Creates and adds a new unattached leaf node to the tree, and returns the node of the new node pub fn new_leaf(&mut self, layout: Style) -> TaffyResult { - if layout.display == Display::Contents { self.contents_count += 1; } + if layout.display == Display::Contents { self.contents_dirty = true; } let id = self.nodes.insert(NodeData::new(layout)); let _ = self.children.insert(new_vec_with_capacity(0)); let _ = self.parents.insert(None); @@ -620,7 +621,7 @@ impl TaffyTree { /// /// Creates and adds a new leaf node with a supplied context pub fn new_leaf_with_context(&mut self, layout: Style, context: NodeContext) -> TaffyResult { - if layout.display == Display::Contents { self.contents_count += 1; } + if layout.display == Display::Contents { self.contents_dirty = true; } let mut data = NodeData::new(layout); data.has_context = true; @@ -635,7 +636,7 @@ impl TaffyTree { /// Creates and adds a new node, which may have any number of `children` pub fn new_with_children(&mut self, layout: Style, children: &[NodeId]) -> TaffyResult { - if layout.display == Display::Contents { self.contents_count += 1; } + if layout.display == Display::Contents { self.contents_dirty = true; } let id = NodeId::from(self.nodes.insert(NodeData::new(layout))); for child in children { @@ -654,7 +655,7 @@ impl TaffyTree { self.children.clear(); self.parents.clear(); self.resolved_children.clear(); - self.contents_count = 0; + self.contents_dirty = false; } /// Remove a specific node from the tree and drop it @@ -662,7 +663,7 @@ impl TaffyTree { /// Returns the id of the node removed. pub fn remove(&mut self, node: NodeId) -> TaffyResult { let key = node.into(); - if self.nodes[key].style.display == Display::Contents { self.contents_count -= 1; } + if self.nodes[key].style.display == Display::Contents { self.contents_dirty = true; } if let Some(parent) = self.parents[key] { if let Some(children) = self.children.get_mut(parent.into()) { children.retain(|f| *f != node); @@ -881,10 +882,8 @@ impl TaffyTree { let key = node.into(); let old_display = self.nodes[key].style.display; let new_display = style.display; - if old_display != Display::Contents && new_display == Display::Contents { - self.contents_count += 1; - } else if old_display == Display::Contents && new_display != Display::Contents { - self.contents_count -= 1; + if old_display == Display::Contents || new_display == Display::Contents { + self.contents_dirty = true; } self.nodes[key].style = style; self.mark_dirty(node)?; @@ -964,8 +963,8 @@ impl TaffyTree { fn resolve_contents_children(&mut self, root: NodeId) { self.resolved_children.clear(); - // Fast path: no contents nodes in the entire tree. - if self.contents_count == 0 { + // Fast path: no contents-related mutations since last resolve. + if !self.contents_dirty { return; } @@ -983,21 +982,26 @@ impl TaffyTree { result }; + let mut found_any = false; for node_id in all_nodes { let key: DefaultKey = node_id.into(); let children = &self.children[key]; - // Fast path: check if any direct child is Display::Contents. let has_contents_child = children.iter().any(|child| { self.nodes[(*child).into()].style.display == Display::Contents }); if has_contents_child { + found_any = true; let mut resolved = ChildrenVec::new(); self.collect_resolved_children(node_id, &mut resolved); self.resolved_children.insert(key, resolved); } } + + // If no contents nodes were found, clear the flag so future layouts + // skip the walk entirely (e.g. after all contents nodes are removed). + self.contents_dirty = found_any; } /// Recursively collect the resolved children for a node, flattening through From 9d6a56c2b0deb8ab14b5ae5db69e69b12350a23c Mon Sep 17 00:00:00 2001 From: RJM Date: Wed, 1 Apr 2026 13:33:34 +1100 Subject: [PATCH 6/6] test: add HTML fixtures and XML tests for Display::Contents 6 browser-verified test cases: - basic (5 items, 2 via contents wrapper) - nested (contents within contents) - deeply nested (3 levels of contents) - single child (GestureDetector use case) - flex-grow through contents - contents vs none side-by-side All expected values verified against Chrome's computed layout. Also adds "contents" to the FromStr parser for Display. --- src/style/mod.rs | 1 + .../contents/contents_flex_basic.html | 23 ++++++++++++ .../contents/contents_flex_deeply_nested.html | 28 +++++++++++++++ .../contents_flex_mixed_with_none.html | 24 +++++++++++++ .../contents/contents_flex_nested.html | 26 ++++++++++++++ .../contents/contents_flex_single_child.html | 21 +++++++++++ .../contents_flex_with_flex_child.html | 22 ++++++++++++ .../contents_flex_basic__border_box_ltr.xml | 25 +++++++++++++ ...nts_flex_deeply_nested__border_box_ltr.xml | 35 +++++++++++++++++++ ...s_flex_mixed_with_none__border_box_ltr.xml | 25 +++++++++++++ .../contents_flex_nested__border_box_ltr.xml | 31 ++++++++++++++++ ...ents_flex_single_child__border_box_ltr.xml | 19 ++++++++++ ...s_flex_with_flex_child__border_box_ltr.xml | 21 +++++++++++ tests/xml/mod.rs | 31 ++++++++++++++++ 14 files changed, 332 insertions(+) create mode 100644 test_fixtures/contents/contents_flex_basic.html create mode 100644 test_fixtures/contents/contents_flex_deeply_nested.html create mode 100644 test_fixtures/contents/contents_flex_mixed_with_none.html create mode 100644 test_fixtures/contents/contents_flex_nested.html create mode 100644 test_fixtures/contents/contents_flex_single_child.html create mode 100644 test_fixtures/contents/contents_flex_with_flex_child.html create mode 100644 tests/xml/contents/contents_flex_basic__border_box_ltr.xml create mode 100644 tests/xml/contents/contents_flex_deeply_nested__border_box_ltr.xml create mode 100644 tests/xml/contents/contents_flex_mixed_with_none__border_box_ltr.xml create mode 100644 tests/xml/contents/contents_flex_nested__border_box_ltr.xml create mode 100644 tests/xml/contents/contents_flex_single_child__border_box_ltr.xml create mode 100644 tests/xml/contents/contents_flex_with_flex_child__border_box_ltr.xml diff --git a/src/style/mod.rs b/src/style/mod.rs index b0ca82893..b69686e3e 100644 --- a/src/style/mod.rs +++ b/src/style/mod.rs @@ -223,6 +223,7 @@ impl Default for Display { #[cfg(feature = "parse")] crate::util::parse::impl_parse_for_keyword_enum!(Display, "none" => None, + "contents" => Contents, #[cfg(feature = "flexbox")] "flex" => Flex, #[cfg(feature = "grid")] diff --git a/test_fixtures/contents/contents_flex_basic.html b/test_fixtures/contents/contents_flex_basic.html new file mode 100644 index 000000000..eee9e648e --- /dev/null +++ b/test_fixtures/contents/contents_flex_basic.html @@ -0,0 +1,23 @@ + + + + + + + Test description + + + + +
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+ + + \ No newline at end of file diff --git a/test_fixtures/contents/contents_flex_deeply_nested.html b/test_fixtures/contents/contents_flex_deeply_nested.html new file mode 100644 index 000000000..86d4afcee --- /dev/null +++ b/test_fixtures/contents/contents_flex_deeply_nested.html @@ -0,0 +1,28 @@ + + + + + + + Test description + + + + +
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+ + + \ No newline at end of file diff --git a/test_fixtures/contents/contents_flex_mixed_with_none.html b/test_fixtures/contents/contents_flex_mixed_with_none.html new file mode 100644 index 000000000..48415deca --- /dev/null +++ b/test_fixtures/contents/contents_flex_mixed_with_none.html @@ -0,0 +1,24 @@ + + + + + + + Test description + + + + + +
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+ + + \ No newline at end of file diff --git a/test_fixtures/contents/contents_flex_nested.html b/test_fixtures/contents/contents_flex_nested.html new file mode 100644 index 000000000..de2898722 --- /dev/null +++ b/test_fixtures/contents/contents_flex_nested.html @@ -0,0 +1,26 @@ + + + + + + + Test description + + + + +
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+ + + \ No newline at end of file diff --git a/test_fixtures/contents/contents_flex_single_child.html b/test_fixtures/contents/contents_flex_single_child.html new file mode 100644 index 000000000..c18209e27 --- /dev/null +++ b/test_fixtures/contents/contents_flex_single_child.html @@ -0,0 +1,21 @@ + + + + + + + Test description + + + + + +
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+ + + \ No newline at end of file diff --git a/test_fixtures/contents/contents_flex_with_flex_child.html b/test_fixtures/contents/contents_flex_with_flex_child.html new file mode 100644 index 000000000..4236c240a --- /dev/null +++ b/test_fixtures/contents/contents_flex_with_flex_child.html @@ -0,0 +1,22 @@ + + + + + + + Test description + + + + + +
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+ + + \ No newline at end of file diff --git a/tests/xml/contents/contents_flex_basic__border_box_ltr.xml b/tests/xml/contents/contents_flex_basic__border_box_ltr.xml new file mode 100644 index 000000000..c6a31b87c --- /dev/null +++ b/tests/xml/contents/contents_flex_basic__border_box_ltr.xml @@ -0,0 +1,25 @@ + + + +
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+ + + + + + + + + + diff --git a/tests/xml/contents/contents_flex_with_flex_child__border_box_ltr.xml b/tests/xml/contents/contents_flex_with_flex_child__border_box_ltr.xml new file mode 100644 index 000000000..20f64ef16 --- /dev/null +++ b/tests/xml/contents/contents_flex_with_flex_child__border_box_ltr.xml @@ -0,0 +1,21 @@ + + + +
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+ + + + + + + + + + + diff --git a/tests/xml/mod.rs b/tests/xml/mod.rs index 7218ac1f7..ad75e1198 100644 --- a/tests/xml/mod.rs +++ b/tests/xml/mod.rs @@ -22913,3 +22913,34 @@ mod leaf { crate::run_xml_test("leaf", "leaf_with_content_and_padding_border__content_box_rtl"); } } +mod contents { + #[test] + fn contents_flex_basic__border_box_ltr() { + crate::run_xml_test("contents", "contents_flex_basic__border_box_ltr"); + } + + #[test] + fn contents_flex_nested__border_box_ltr() { + crate::run_xml_test("contents", "contents_flex_nested__border_box_ltr"); + } + + #[test] + fn contents_flex_single_child__border_box_ltr() { + crate::run_xml_test("contents", "contents_flex_single_child__border_box_ltr"); + } + + #[test] + fn contents_flex_with_flex_child__border_box_ltr() { + crate::run_xml_test("contents", "contents_flex_with_flex_child__border_box_ltr"); + } + + #[test] + fn contents_flex_mixed_with_none__border_box_ltr() { + crate::run_xml_test("contents", "contents_flex_mixed_with_none__border_box_ltr"); + } + + #[test] + fn contents_flex_deeply_nested__border_box_ltr() { + crate::run_xml_test("contents", "contents_flex_deeply_nested__border_box_ltr"); + } +}