Add method to write VT/ANSI control codes

Adds a new extension method IAnsiConsole.WriteAnsi that writes
VT/ANSI control codes to the console. If VT/ANSI control codes are
not supported, nothing will be written.

src/Spectre.Console.Testing/TestConsoleExtensions.cs

@@ -17,6 +17,18 @@ namespace Spectre.Console.Testing
             return console;
         }
 
+        /// <summary>
+        /// Sets whether or not ANSI is supported.
+        /// </summary>
+        /// <param name="console">The console.</param>
+        /// <param name="enable">Whether or not VT/ANSI control codes are supported.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static TestConsole SupportsAnsi(this TestConsole console, bool enable)
+        {
+            console.Profile.Capabilities.Ansi = enable;
+            return console;
+        }
+
         /// <summary>
         /// Makes the console interactive.
         /// </summary>

src/Spectre.Console.Tests/Unit/AnsiConsoleTests.Advanced.cs

@@ -0,0 +1,47 @@
+using Shouldly;
+using Spectre.Console.Advanced;
+using Spectre.Console.Testing;
+using Xunit;
+
+namespace Spectre.Console.Tests.Unit
+{
+    public partial class AnsiConsoleTests
+    {
+        public sealed class Advanced
+        {
+            [Fact]
+            public void Should_Write_Ansi_Codes_To_Console_If_Supported()
+            {
+                // Given
+                var console = new TestConsole()
+                    .SupportsAnsi(true)
+                    .Colors(ColorSystem.Standard)
+                    .EmitAnsiSequences();
+
+                // When
+                console.WriteAnsi("Hello");
+
+                // Then
+                console.Output.NormalizeLineEndings()
+                    .ShouldBe("Hello");
+            }
+
+            [Fact]
+            public void Should_Not_Write_Ansi_Codes_To_Console_If_Not_Supported()
+            {
+                // Given
+                var console = new TestConsole()
+                    .SupportsAnsi(false)
+                    .Colors(ColorSystem.Standard)
+                    .EmitAnsiSequences();
+
+                // When
+                console.WriteAnsi("Hello");
+
+                // Then
+                console.Output.NormalizeLineEndings()
+                    .ShouldBeEmpty();
+            }
+        }
+    }
+}

src/Spectre.Console.Tests/Unit/AnsiConsoleTests.cs

@@ -6,6 +6,8 @@ using Xunit;
 namespace Spectre.Console.Tests.Unit
 {
     public partial class AnsiConsoleTests
+    {
+        public sealed class Clear
         {
             [Theory]
             [InlineData(false, "HelloWorld")]
@@ -25,7 +27,10 @@ namespace Spectre.Console.Tests.Unit
                 // Then
                 console.Output.ShouldBe(expected);
             }
+        }
 
+        public sealed class Write
+        {
             [Fact]
             public void Should_Combine_Decoration_And_Colors()
             {
@@ -105,6 +110,7 @@ namespace Spectre.Console.Tests.Unit
                 // Then
                 console.Output.ShouldBe("\u001b[90;47mHello\u001b[0m");
             }
+        }
 
         public sealed class WriteLine
         {

src/Spectre.Console/Capabilities.cs

@@ -16,7 +16,7 @@ namespace Spectre.Console
 
         /// <summary>
         /// Gets or sets a value indicating whether or not
-        /// the console supports Ansi.
+        /// the console supports VT/ANSI control codes.
         /// </summary>
         public bool Ansi { get; set; }
 

src/Spectre.Console/Extensions/Advanced/AnsiConsoleExtensions.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace Spectre.Console.Advanced
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="IAnsiConsole"/>.
+    /// </summary>
+    public static class AnsiConsoleExtensions
+    {
+        /// <summary>
+        /// Writes a VT/Ansi control code sequence to the console (if supported).
+        /// </summary>
+        /// <param name="console">The console to write to.</param>
+        /// <param name="sequence">The VT/Ansi control code sequence to write.</param>
+        public static void WriteAnsi(this IAnsiConsole console, string sequence)
+        {
+            if (console is null)
+            {
+                throw new ArgumentNullException(nameof(console));
+            }
+
+            if (console.Profile.Capabilities.Ansi)
+            {
+                console.Write(new ControlCode(sequence));
+            }
+        }
+    }
+}

src/Spectre.Console/Extensions/AnsiConsoleExtensions.cs

@@ -38,6 +38,11 @@ namespace Spectre.Console
         /// <param name="text">The text to write.</param>
         public static void Write(this IAnsiConsole console, string text)
         {
+            if (console is null)
+            {
+                throw new ArgumentNullException(nameof(console));
+            }
+
             console.Write(new Text(text, Style.Plain));
         }
 
@@ -49,6 +54,11 @@ namespace Spectre.Console
         /// <param name="style">The text style.</param>
         public static void Write(this IAnsiConsole console, string text, Style style)
         {
+            if (console is null)
+            {
+                throw new ArgumentNullException(nameof(console));
+            }
+
             console.Write(new Text(text, style));
         }
 

src/Spectre.Console/IReadOnlyCapabilities.cs

@@ -14,7 +14,7 @@ namespace Spectre.Console
 
         /// <summary>
         /// Gets a value indicating whether or not
-        /// the console supports Ansi.
+        /// the console supports VT/ANSI control codes.
         /// </summary>
         bool Ansi { get; }
 

src/Spectre.Console/Internal/Backends/Ansi/AnsiConsoleBackend.cs

@@ -22,12 +22,12 @@ namespace Spectre.Console
 
         public void Clear(bool home)
         {
-            Write(new ControlSequence(ED(2)));
+            Write(new ControlCode(ED(2)));
-            Write(new ControlSequence(ED(3)));
+            Write(new ControlCode(ED(3)));
 
             if (home)
             {
-                Write(new ControlSequence(CUP(1, 1)));
+                Write(new ControlCode(CUP(1, 1)));
             }
         }
 

src/Spectre.Console/Internal/Backends/Ansi/AnsiConsoleCursor.cs

@@ -16,11 +16,11 @@ namespace Spectre.Console
         {
             if (show)
             {
-                _backend.Write(new ControlSequence(SM(DECTCEM)));
+                _backend.Write(new ControlCode(SM(DECTCEM)));
             }
             else
             {
-                _backend.Write(new ControlSequence(RM(DECTCEM)));
+                _backend.Write(new ControlCode(RM(DECTCEM)));
             }
         }
 
@@ -34,23 +34,23 @@ namespace Spectre.Console
             switch (direction)
             {
                 case CursorDirection.Up:
-                    _backend.Write(new ControlSequence(CUU(steps)));
+                    _backend.Write(new ControlCode(CUU(steps)));
                     break;
                 case CursorDirection.Down:
-                    _backend.Write(new ControlSequence(CUD(steps)));
+                    _backend.Write(new ControlCode(CUD(steps)));
                     break;
                 case CursorDirection.Right:
-                    _backend.Write(new ControlSequence(CUF(steps)));
+                    _backend.Write(new ControlCode(CUF(steps)));
                     break;
                 case CursorDirection.Left:
-                    _backend.Write(new ControlSequence(CUB(steps)));
+                    _backend.Write(new ControlCode(CUB(steps)));
                     break;
             }
         }
 
         public void SetPosition(int column, int line)
         {
-            _backend.Write(new ControlSequence(CUP(line, column)));
+            _backend.Write(new ControlCode(CUP(line, column)));
         }
     }
 }

src/Spectre.Console/Rendering/LiveRenderable.cs

@@ -25,11 +25,11 @@ namespace Spectre.Console.Rendering
             {
                 if (_shape == null)
                 {
-                    return new ControlSequence(string.Empty);
+                    return new ControlCode(string.Empty);
                 }
 
                 var linesToMoveUp = _shape.Value.Height - 1;
-                return new ControlSequence("\r" + CUU(linesToMoveUp));
+                return new ControlCode("\r" + CUU(linesToMoveUp));
             }
         }
 
@@ -39,11 +39,11 @@ namespace Spectre.Console.Rendering
             {
                 if (_shape == null)
                 {
-                    return new ControlSequence(string.Empty);
+                    return new ControlCode(string.Empty);
                 }
 
                 var linesToClear = _shape.Value.Height - 1;
-                return new ControlSequence("\r" + EL(2) + (CUU(1) + EL(2)).Repeat(linesToClear));
+                return new ControlCode("\r" + EL(2) + (CUU(1) + EL(2)).Repeat(linesToClear));
             }
         }
 

src/Spectre.Console/Rendering/RenderContext.cs

@@ -14,6 +14,11 @@ namespace Spectre.Console.Rendering
         /// </summary>
         public ColorSystem ColorSystem => _capabilities.ColorSystem;
 
+        /// <summary>
+        /// Gets a value indicating whether or not VT/Ansi codes are supported.
+        /// </summary>
+        public bool Ansi => _capabilities.Ansi;
+
         /// <summary>
         /// Gets a value indicating whether or not unicode is supported.
         /// </summary>

src/Spectre.Console/Widgets/ControlCode.cs

@@ -3,11 +3,11 @@ using Spectre.Console.Rendering;
 
 namespace Spectre.Console
 {
-    internal sealed class ControlSequence : Renderable
+    internal sealed class ControlCode : Renderable
     {
         private readonly Segment _segment;
 
-        public ControlSequence(string control)
+        public ControlCode(string control)
         {
             _segment = Segment.Control(control);
         }
@@ -18,8 +18,11 @@ namespace Spectre.Console
         }
 
         protected override IEnumerable<Segment> Render(RenderContext context, int maxWidth)
+        {
+            if (context.Ansi)
             {
                 yield return _segment;
             }
         }
+    }
 }

src/Spectre.Console/Widgets/Progress/ProgressContext.cs

@@ -73,7 +73,7 @@ namespace Spectre.Console
         public void Refresh()
         {
             _renderer.Update(this);
-            _console.Write(new ControlSequence(string.Empty));
+            _console.Write(new ControlCode(string.Empty));
         }
 
         internal IReadOnlyList<ProgressTask> GetTasks()

src/Spectre.Console/Widgets/Prompt/Rendering/RenderableList.cs

@@ -38,7 +38,7 @@ namespace Spectre.Console
 
         public void Redraw()
         {
-            _console.Write(new ControlSequence(string.Empty));
+            _console.Write(new ControlCode(string.Empty));
         }
 
         public bool Update(ConsoleKey key)