Hover tooltips for metadata cells

MetadataCellTooltip resolves `{ColumnName}Tooltip` on the bound row by
reflection. The view subscribes to PointerMoved, walks up to the
DataGridCell under the pointer, and applies the resolved string via
ToolTip.SetTip whenever the cell changes.

Assisted-by: Claude:claude-opus-4-7:Claude Code

ILSpy.Tests/Metadata/MetadataCellTooltipTests.cs

@@ -0,0 +1,78 @@
+// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using AwesomeAssertions;
+
+using ILSpy.Metadata;
+
+using NUnit.Framework;
+
+namespace ICSharpCode.ILSpy.Tests.Metadata;
+
+[TestFixture]
+public class MetadataCellTooltipTests
+{
+	sealed class EntryWithTooltips
+	{
+		public string Name { get; set; } = "Foo";
+		public string NameTooltip => $"heap-offset for \"{Name}\"";
+
+		public int Flags { get; set; } = 0x42;
+		// Non-string tooltip values flow through ToString() — the helper just normalises
+		// whatever the entry exposes into a string, leaving styled-tooltip rendering for
+		// a later phase.
+		public object FlagsTooltip => $"Flags=0x{Flags:X4}";
+	}
+
+	sealed class EntryWithoutTooltips
+	{
+		public string Name { get; set; } = "Bar";
+	}
+
+	[Test]
+	public void Resolve_Returns_String_Tooltip_When_Property_Is_Present()
+	{
+		// The convention is `{columnName}Tooltip` — looked up by reflection on the bound row.
+		var entry = new EntryWithTooltips { Name = "System.Object" };
+		MetadataCellTooltip.Resolve(entry, "Name").Should().Be("heap-offset for \"System.Object\"");
+	}
+
+	[Test]
+	public void Resolve_Returns_Null_When_The_Tooltip_Property_Is_Missing()
+	{
+		// Many entry types expose tooltips for only a subset of columns; missing means "no
+		// tooltip", not "throw".
+		var entry = new EntryWithoutTooltips();
+		MetadataCellTooltip.Resolve(entry, "Name").Should().BeNull();
+	}
+
+	[Test]
+	public void Resolve_Stringifies_Non_String_Tooltip_Values()
+	{
+		// Some WPF entries return rich FlagsTooltip objects; stringification is the safe
+		// fallback so the helper still produces something usable.
+		var entry = new EntryWithTooltips { Flags = 0x1234 };
+		MetadataCellTooltip.Resolve(entry, "Flags").Should().Be("Flags=0x1234");
+	}
+
+	[Test]
+	public void Resolve_Returns_Null_When_The_Item_Is_Null()
+	{
+		MetadataCellTooltip.Resolve(null!, "Name").Should().BeNull();
+	}
+}

ILSpy/Metadata/MetadataCellTooltip.cs

@@ -0,0 +1,57 @@
+// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+using System.Collections.Concurrent;
+using System.Reflection;
+
+namespace ILSpy.Metadata
+{
+	/// <summary>
+	/// Resolves per-cell tooltips for a metadata-table row. Entry classes opt in by exposing
+	/// a public <c>{ColumnName}Tooltip</c> property — <c>NameTooltip</c>, <c>FlagsTooltip</c>,
+	/// <c>BaseTypeTooltip</c>, and so on. The resolver returns a stringified rendering, so
+	/// callers can flow it straight into <c>ToolTip.SetTip</c>.
+	/// </summary>
+	public static class MetadataCellTooltip
+	{
+		static readonly ConcurrentDictionary<(Type Type, string Column), PropertyInfo?> propertyCache = new();
+
+		/// <summary>
+		/// Looks up <paramref name="columnName"/><c>Tooltip</c> on <paramref name="item"/>'s
+		/// runtime type. Returns the property's stringified value, or <see langword="null"/>
+		/// if the item is null, the tooltip property is absent, or the value is null / blank.
+		/// </summary>
+		public static string? Resolve(object item, string columnName)
+		{
+			if (item is null)
+				return null;
+			var prop = propertyCache.GetOrAdd((item.GetType(), columnName),
+				static key => key.Type.GetProperty(key.Column + "Tooltip",
+					BindingFlags.Public | BindingFlags.Instance));
+			if (prop is null)
+				return null;
+			object? value;
+			try
+			{ value = prop.GetValue(item); }
+			catch { return null; }
+			var s = value?.ToString();
+			return string.IsNullOrWhiteSpace(s) ? null : s;
+		}
+	}
+}

ILSpy/Views/MetadataTablePage.axaml.cs

@@ -19,10 +19,14 @@
 using System;
 using System.ComponentModel;
 
+using Avalonia;
 using Avalonia.Collections;
 using Avalonia.Controls;
+using Avalonia.Input;
 using Avalonia.Markup.Xaml;
+using Avalonia.VisualTree;
 
+using ILSpy.Metadata;
 using ILSpy.ViewModels;
 
 namespace ILSpy.Views
@@ -37,15 +41,38 @@ namespace ILSpy.Views
 	{
 		MetadataTablePageModel? boundModel;
 		DataGridCollectionView? itemsView;
+		DataGridCell? hoveredCell;
 
 		public MetadataTablePage()
 		{
 			InitializeComponent();
 			DataContextChanged += (_, _) => RebindModel();
+			AddHandler(PointerMovedEvent, OnPointerMovedOverGrid);
 		}
 
 		void InitializeComponent() => AvaloniaXamlLoader.Load(this);
 
+		void OnPointerMovedOverGrid(object? sender, PointerEventArgs e)
+		{
+			// Walk up the visual tree from the pointer's source to the cell. Cells nest
+			// arbitrary content (TextBlock for plain columns, Button for token columns), so
+			// a per-cell PointerEntered subscription would miss most events.
+			var visual = e.Source as Visual;
+			while (visual is not null and not DataGridCell)
+				visual = visual.GetVisualParent();
+			var cell = visual as DataGridCell;
+			if (cell == hoveredCell)
+				return;
+			hoveredCell = cell;
+			if (cell is null)
+				return;
+			var columnName = cell.OwningColumn?.Header?.ToString();
+			if (columnName is null)
+				return;
+			var tip = MetadataCellTooltip.Resolve(cell.DataContext!, columnName);
+			ToolTip.SetTip(cell, tip);
+		}
+
 		void RebindModel()
 		{
 			if (boundModel != null)