fix(ios): honor layout weight in stacks

guides/components.md

@@ -199,6 +199,10 @@ cancel_tap = {self(), :cancel}
 """
 ```
 
+A single weighted child expands into the parent's remaining main-axis space. Multiple
+weighted children divide that space evenly on iOS; Android additionally honors unequal
+numeric ratios. Weight values must be positive. Use equal weights for cross-platform layouts.
+
 ### `:box`
 
 A single-child container. Use it to add background, padding, or corner radius to a child:

ios/MobNode.h

@@ -173,7 +173,8 @@ NS_ASSUME_NONNULL_BEGIN
 @property(nonatomic, strong, nullable) UIColor *color; // track / indicator color
 
 // Layout behaviour
-@property(nonatomic) BOOL fillWidth; // fill parent width (default NO; button default YES)
+@property(nonatomic) CGFloat layoutWeight; // positive = expand on a row/column's main axis
+@property(nonatomic) BOOL fillWidth; // fill parent width (default NO; button default YES)
 @property(nonatomic)
  BOOL fillHeight; // fill parent height (default NO) — used for full-screen overlays/dialogs
 @property(nonatomic) CGFloat cornerRadius; // rounded corners in pt (default 0)

ios/MobNode.m

@@ -35,6 +35,7 @@ - (instancetype)init {
  _contentModeStr = @"fit";
  _fixedWidth = 0.0;
  _fixedHeight = 0.0;
+ _layoutWeight = 0.0;
  _fillWidth = NO;
  _cornerRadius = 0.0;
  _nativeViewHandle = -1; // -1 = no native component slot assigned (MOB-100)

ios/MobRootView.swift

@@ -47,6 +47,11 @@
  }
 }
 
+enum MobLayoutWeightAxis {
+ case horizontal
+ case vertical
+}
+
 extension View {
  @ViewBuilder
  func ifLet<T>(_ value: T?, transform: (Self, T) -> some View) -> some View {
@@ -241,13 +246,21 @@
 
 struct MobNodeView: View {
  let node: MobNode
+ private let layoutWeightAxis: MobLayoutWeightAxis?
+
+ init(node: MobNode, layoutWeightAxis: MobLayoutWeightAxis? = nil) {
+ self.node = node
+ self.layoutWeightAxis = layoutWeightAxis
+ }
 
  var body: some View {
  Group {
  switch node.nodeType {
  case .column:
  VStack(alignment: .leading, spacing: 0) {
- ForEach(Array(node.childNodes.enumerated()), id: \.offset) { _, child in MobNodeView(node: child) }
+ ForEach(Array(node.childNodes.enumerated()), id: \.offset) { _, child in
+ MobNodeView(node: child, layoutWeightAxis: .vertical)
+ }
  }
  // fill_height: true lets a column flex to fill its parent so children
  // with Spacer() or fill_height of their own can pin to the bottom.
@@ -272,7 +285,9 @@
  }
  }()
  HStack(alignment: alignment, spacing: 0) {
- ForEach(Array(node.childNodes.enumerated()), id: \.offset) { _, child in MobNodeView(node: child) }
+ ForEach(Array(node.childNodes.enumerated()), id: \.offset) { _, child in
+ MobNodeView(node: child, layoutWeightAxis: .horizontal)
+ }
  }
  // Without maxWidth: .infinity an HStack hugs its content.
  // Flex Spacers inside then have nothing to expand into and
@@ -513,6 +528,12 @@
  EmptyView()
  }
  }
+ // Weight sizing must wrap the node's own visual decoration. Applying
+ // the frame from the parent after MobNodeView has painted its
+ // background leaves an expanded transparent region around a
+ // content-sized fill. Repaint that decoration on the weighted frame
+ // so iOS matches Compose's weight-before-nodeModifier ordering.
+ .modifier(MobLayoutWeight(node: node, axis: layoutWeightAxis))
  // Per-node offset — applied uniformly to every node type. Default is
  // (0, 0) which is a no-op. Used by SquareTriangle's hexagonal
  // snowflake to position rings absolutely within a center-aligned box.
@@ -524,6 +545,36 @@
  }
 }
 
+private struct MobLayoutWeight: ViewModifier {
+ let node: MobNode
+ let axis: MobLayoutWeightAxis?
+
+ @ViewBuilder
+ func body(content: Content) -> some View {
+ if node.layoutWeight > 0, let axis {
+ switch axis {
+ case .horizontal:
+ decorate(content.frame(maxWidth: .infinity, alignment: .leading))
+ case .vertical:
+ decorate(content.frame(maxHeight: .infinity, alignment: .top))
+ }
+ } else {
+ content
+ }
+ }
+
+ private func decorate(_ content: some View) -> some View {
+ content
+ .mobBoxBackground(node: node)
+ .overlay(
+ RoundedRectangle(cornerRadius: node.cornerRadius)
+ .stroke(node.borderColor.map { Color($0) } ?? Color.clear,
+ lineWidth: node.borderWidth)
+ .allowsHitTesting(false)
+ )
+ }
+}
+
 // MobFrameTracker — for any node with an :id, set it as the accessibility
 // identifier and report the element's global frame (logical points) to the C
 // registry as it lays out / moves. Untagged nodes pass through untouched, so
@@ -1149,7 +1200,7 @@
 // no manual frame management required.
 private class CameraPreviewUIView: UIView {
  override class var layerClass: AnyClass { AVCaptureVideoPreviewLayer.self }
  var cameraLayer: AVCaptureVideoPreviewLayer { layer as! AVCaptureVideoPreviewLayer }
 }
 
 private struct MobCameraPreviewView: UIViewRepresentable {
@@ -1969,4 +2020,4 @@
  }
  }
  }
 }

ios/mob_nif.m

@@ -1073,6 +1073,10 @@ static void mob_send_change_float(int handle, double value) {
  if (fixedHeight)
  node.fixedHeight = [fixedHeight doubleValue];
 
+ id layoutWeight = props[@"weight"];
+ if (layoutWeight)
+ node.layoutWeight = [layoutWeight doubleValue];
+
  id cornerRadius = props[@"corner_radius"];
  if (cornerRadius)
  node.cornerRadius = [cornerRadius doubleValue];

test/mob/native_layout_weight_test.exs

@@ -0,0 +1,29 @@
+# These source-contract tests guard native SwiftUI behavior that Elixir cannot execute.
+# credo:disable-for-this-file Jump.CredoChecks.VacuousTest
+defmodule Mob.NativeLayoutWeightTest do
+ use ExUnit.Case, async: true
+
+ @ios Path.expand("../../ios", __DIR__)
+
+ test "iOS parses layout weight at the native boundary" do
+ header = File.read!(Path.join(@ios, "MobNode.h"))
+ implementation = File.read!(Path.join(@ios, "MobNode.m"))
+ nif = File.read!(Path.join(@ios, "mob_nif.m"))
+
+ assert header =~ "CGFloat layoutWeight"
+ assert implementation =~ "_layoutWeight = 0.0"
+ assert nif =~ ~s|props[@"weight"]|
+ assert nif =~ "node.layoutWeight = [layoutWeight doubleValue]"
+ end
+
+ test "iOS expands weighted children on their parent's main axis" do
+ source = File.read!(Path.join(@ios, "MobRootView.swift"))
+
+ assert source =~ "MobNodeView(node: child, layoutWeightAxis: .vertical)"
+ assert source =~ "MobNodeView(node: child, layoutWeightAxis: .horizontal)"
+ assert source =~ ".modifier(MobLayoutWeight(node: node, axis: layoutWeightAxis))"
+ assert source =~ "frame(maxHeight: .infinity, alignment: .top)"
+ assert source =~ "frame(maxWidth: .infinity, alignment: .leading)"
+ assert source =~ ".mobBoxBackground(node: node)"
+ end
+end