Leave a collapsed child out of a horizontal StackPanel's measured height [patch]

TUI.Test/StackPanelTests.cs

@@ -628,6 +628,43 @@ public void StackPanelVerticalDrawsEveryWrappedLineOfTextInsideABorder()
 		Assert.AreEqual(new Position(1, 2), Assert.ContainsSingle(provider.WritesOf("world foo")).Position);
 	}
 
+	/// <summary>
+	/// Tests that a horizontal panel does not ask for the height of a child it collapses for lack of
+	/// width, so a tall child that no longer fits leaves no blank rows and later siblings move up
+	/// (ktsu-dev/TUI#224).
+	/// </summary>
+	[TestMethod]
+	public void StackPanelHorizontalRequiredHeightIgnoresChildrenThatDoNotFit()
+	{
+		TextElement wide = new(new string('A', 20));
+		TextElement tall = new("l1\nl2\nl3\nl4\nl5");
+		StackPanel row = new(Orientation.Horizontal) { wide, tall };
+		TextElement footer = new("footer");
+		StackPanel root = [row, footer];
+		root.Dimensions = new Dimensions(20, 10);
+
+		root.ArrangeChildren();
+		row.ArrangeChildren();
+
+		Assert.AreEqual(new Dimensions(20, 1), row.CalculateRequiredDimensions(20));
+		Assert.AreEqual(Dimensions.Empty, tall.Dimensions);
+		Assert.AreEqual(new Dimensions(20, 1), row.Dimensions);
+		Assert.AreEqual(1, footer.Position.Y);
+	}
+
+	/// <summary>
+	/// Tests that a horizontal panel still measures every child when no width constrains it.
+	/// </summary>
+	[TestMethod]
+	public void StackPanelHorizontalUnconstrainedMeasureCountsEveryChild()
+	{
+		StackPanel row = new(Orientation.Horizontal) { Spacing = 1 };
+		row.Add(new TextElement(new string('A', 20)));
+		row.Add(new TextElement("l1\nl2\nl3\nl4\nl5"));
+
+		Assert.AreEqual(new Dimensions(23, 5), row.CalculateRequiredDimensions());
+	}
+
 	/// <summary>
 	/// Tests that a horizontal panel measures word-wrapped text against the width it has, so it
 	/// reports the wrapped height to a parent rather than one row (ktsu-dev/TUI#161).

TUI/Elements/Layouts/StackPanel.cs

@@ -165,11 +165,20 @@ private Dimensions CalculateRequiredDimensionsForChildren(int? availableWidth)
 		int maxHeight = 0;
 
 		IUIElement[] visibleChildren = [.. GetVisibleChildren()];
-		int totalSpacing = Math.Max(0, (visibleChildren.Length - 1) * Spacing);
+		int measuredChildren = 0;
 		int consumedWidth = 0;
 
 		foreach (IUIElement? child in visibleChildren)
 		{
+			// A horizontal child that starts where the width has run out is collapsed when arranged,
+			// so it adds neither width nor height, matching the arrange pass's break (ktsu-dev/TUI#224).
+			if (Orientation == Orientation.Horizontal && availableWidth is int limit && consumedWidth >= limit)
+			{
+				break;
+			}
+
+			measuredChildren++;
+
 			// A horizontal child gets the width its earlier siblings and the spacing between them
 			// leave, as it does when arranged (ktsu-dev/TUI#161).
 			Dimensions childDimensions = availableWidth switch
@@ -192,6 +201,8 @@ private Dimensions CalculateRequiredDimensionsForChildren(int? availableWidth)
 			}
 		}
 
+		int totalSpacing = Math.Max(0, (measuredChildren - 1) * Spacing);
+
 		return Orientation == Orientation.Vertical
 			? new Dimensions(maxWidth, totalHeight + totalSpacing)
 			: new Dimensions(totalWidth + totalSpacing, maxHeight);