Add tree widget

src/Spectre.Console/Rendering/AsciiTreeRendering.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace Spectre.Console.Rendering
+{
+    /// <summary>
+    /// An ASCII rendering of a tree.
+    /// </summary>
+    public sealed class AsciiTreeRendering : ITreeRendering
+    {
+        /// <inheritdoc/>
+        public string GetPart(TreePart part)
+        {
+            return part switch
+            {
+                TreePart.SiblingConnector => "│   ",
+                TreePart.ChildBranch => "├── ",
+                TreePart.BottomChildBranch => "└── ",
+                _ => throw new ArgumentOutOfRangeException(nameof(part), part, "Unknown tree part."),
+            };
+        }
+
+        /// <inheritdoc/>
+        public int PartSize => 4;
+    }
+}

src/Spectre.Console/Rendering/ITreeRendering.cs

@@ -0,0 +1,20 @@
+namespace Spectre.Console.Rendering
+{
+    /// <summary>
+    /// Represents the characters used to render a tree.
+    /// </summary>
+    public interface ITreeRendering
+    {
+        /// <summary>
+        /// Get the set of characters used to render the corresponding <see cref="TreePart"/>.
+        /// </summary>
+        /// <param name="part">The part of the tree to get rendering string for.</param>
+        /// <returns>Rendering string for the tree part.</returns>
+        string GetPart(TreePart part);
+
+        /// <summary>
+        /// Gets the length of all tree part strings.
+        /// </summary>
+        int PartSize { get; }
+    }
+}

src/Spectre.Console/Rendering/Segment.cs

@@ -52,6 +52,13 @@ namespace Spectre.Console.Rendering
         /// </summary>
         public static Segment Empty { get; } = new Segment(string.Empty, Style.Plain, false, false);
 
+        /// <summary>
+        /// Creates padding segment.
+        /// </summary>
+        /// <param name="size">Number of whitespace characters.</param>
+        /// <returns>Segment for specified padding size.</returns>
+        public static Segment Padding(int size) => new(new string(' ', size));
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Segment"/> class.
         /// </summary>

src/Spectre.Console/Rendering/SegmentShape.cs

@@ -48,7 +48,7 @@ namespace Spectre.Console.Rendering
                 var missing = Width - length;
                 if (missing > 0)
                 {
-                    line.Add(new Segment(new string(' ', missing)));
+                    line.Add(Segment.Padding(missing));
                 }
             }
 
@@ -59,7 +59,7 @@ namespace Spectre.Console.Rendering
                 {
                     lines.Add(new SegmentLine
                     {
-                        new Segment(new string(' ', Width)),
+                        Segment.Padding(Width),
                     });
                 }
             }

src/Spectre.Console/Rendering/TreePart.cs

@@ -0,0 +1,23 @@
+namespace Spectre.Console.Rendering
+{
+    /// <summary>
+    /// Defines the different rendering parts of a <see cref="Tree"/>.
+    /// </summary>
+    public enum TreePart
+    {
+        /// <summary>
+        /// Connection between siblings.
+        /// </summary>
+        SiblingConnector,
+
+        /// <summary>
+        /// Branch from parent to child.
+        /// </summary>
+        ChildBranch,
+
+        /// <summary>
+        /// Branch from parent to child for the last child in a set.
+        /// </summary>
+        BottomChildBranch,
+    }
+}

src/Spectre.Console/Rendering/TreeRendering.cs

@@ -0,0 +1,13 @@
+namespace Spectre.Console.Rendering
+{
+    /// <summary>
+    /// Selection of different renderings which can be used by <see cref="Tree"/>.
+    /// </summary>
+    public static class TreeRendering
+    {
+        /// <summary>
+        /// Gets ASCII rendering of a tree.
+        /// </summary>
+        public static ITreeRendering Ascii { get; } = new AsciiTreeRendering();
+    }
+}