Measure a container with no room past its padding as the padding alone [patch]

TUI.Test/ContainerNoRoomMeasureTests.cs

@@ -0,0 +1,69 @@
+// Copyright (c) 2023-2026 ktsu-dev contributors
+
+namespace ktsu.TUI.Test;
+
+using ktsu.TUI.Core.Elements.Layouts;
+using ktsu.TUI.Core.Elements.Primitives;
+using ktsu.TUI.Core.Models;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+/// <summary>
+/// Tests for a container measured at a width its padding takes entirely (ktsu-dev/TUI#249).
+/// </summary>
+/// <remarks>
+/// The container measured its children at width 0, which <see cref="TextElement"/> reads as "no
+/// constraint", so a word-wrapped child reported its full unwrapped height for text that could
+/// never be drawn, and the rows it claimed were taken from the siblings below.
+/// </remarks>
+[TestClass]
+public sealed class ContainerNoRoomMeasureTests
+{
+	/// <summary>
+	/// A border measured at width 1 or 2 reports the bare border, whatever its child is.
+	/// </summary>
+	/// <param name="availableWidth">A width no wider than the border's padding.</param>
+	[TestMethod]
+	[DataRow(1)]
+	[DataRow(2)]
+	public void BorderWithNoRoomForItsChildMeasuresAsTheBareBorder(int availableWidth)
+	{
+		BorderElement border = new() { Child = new TextElement("one\ntwo\nthree\nfour\nfive") { WordWrap = true } };
+
+		Assert.AreEqual(new Dimensions(2, 2), border.CalculateRequiredDimensions(availableWidth));
+	}
+
+	/// <summary>
+	/// A border given one more column than its padding still measures its child.
+	/// </summary>
+	[TestMethod]
+	public void BorderWithOneColumnOfRoomStillMeasuresItsChild()
+	{
+		BorderElement border = new() { Child = new TextElement("ab") { WordWrap = true } };
+
+		Assert.AreEqual(new Dimensions(3, 4), border.CalculateRequiredDimensions(3));
+	}
+
+	/// <summary>
+	/// The issue's layout: a border squeezed to its padding width beside a label leaves the row
+	/// below where the bare border ends, not where its unwrapped child would.
+	/// </summary>
+	[TestMethod]
+	public void SqueezedBorderDoesNotPushTheNextRowDown()
+	{
+		BorderElement border = new() { Child = new TextElement("one\ntwo\nthree\nfour\nfive") { WordWrap = true } };
+		StackPanel row = new(Orientation.Horizontal);
+		row.AddChild(new TextElement("Label text here: "));
+		row.AddChild(border);
+		StackPanel panel = new(Orientation.Vertical);
+		panel.AddChild(row);
+		panel.AddChild(new TextElement("below"));
+		panel.Position = Position.Origin;
+		panel.Dimensions = new Dimensions(19, 20);
+		RecordingConsoleProvider provider = new();
+
+		panel.ArrangeChildren();
+		panel.Render(provider);
+
+		Assert.AreEqual(2, provider.WritesOf("below").Single().Position.Y);
+	}
+}

TUI/Elements/UIContainerBase.cs

@@ -141,7 +141,16 @@ protected override Dimensions OnCalculateRequiredDimensions()
 	/// <inheritdoc />
 	protected override Dimensions OnCalculateRequiredDimensions(int availableWidth)
 	{
-		Dimensions requiredDimensions = OnCalculateRequiredDimensionsForChildren(Math.Max(0, availableWidth - Padding.Horizontal));
+		if (availableWidth > 0 && availableWidth <= Padding.Horizontal)
+		{
+			// The padding takes every column, so no child can be drawn. Measuring the children at
+			// width 0 would read as "no constraint", and a word-wrapped child would then claim its
+			// full unwrapped height in rows that never show, taking them from the siblings below
+			// (ktsu-dev/TUI#249, the container route to ktsu-dev/TUI#198).
+			return Dimensions.Empty.WithPadding(Padding);
+		}
+
+		Dimensions requiredDimensions = OnCalculateRequiredDimensionsForChildren(availableWidth - Padding.Horizontal);
 		return requiredDimensions.WithPadding(Padding);
 	}