Adding Placeholder to TextPrompt

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

@@ -5,17 +5,23 @@ namespace Spectre.Console;
 /// </summary>
 public static partial class AnsiConsoleExtensions
 {
-    internal static async Task<string> ReadLine(this IAnsiConsole console, Style? style, bool secret, char? mask, IEnumerable<string>? items = null, CancellationToken cancellationToken = default)
+    internal static async Task<string> ReadLine(this IAnsiConsole console, Style? style, bool secret, char? mask, IEnumerable<string>? items = null, string? placeholder = null, Style? placeholderStyle = null, CancellationToken cancellationToken = default)
     {
         if (console is null)
         {
             throw new ArgumentNullException(nameof(console));
         }
 
         style ??= Style.Plain;
+        placeholderStyle ??= new Style(foreground: Color.Grey);
         var text = string.Empty;
+        var showPlaceholder = !string.IsNullOrEmpty(placeholder);
 
         var autocomplete = new List<string>(items ?? Enumerable.Empty<string>());
+        if (showPlaceholder && string.IsNullOrEmpty(text))
+        {
+            console.Write(placeholder!, placeholderStyle);
+        }
 
         while (true)
         {
@@ -29,6 +35,11 @@ internal static async Task<string> ReadLine(this IAnsiConsole console, Style? st
             var key = rawKey.Value;
             if (key.Key == ConsoleKey.Enter)
             {
+                if (showPlaceholder && string.IsNullOrEmpty(text))
+                {
+                    console.Write("\b \b".Repeat(placeholder!.Length));
+                }
+
                 return text;
             }
 
@@ -73,6 +84,13 @@ internal static async Task<string> ReadLine(this IAnsiConsole console, Style? st
 
             if (!char.IsControl(key.KeyChar))
             {
+                // Delete place holder when a key is press
+                if (showPlaceholder && string.IsNullOrEmpty(text))
+                {
+                    console.Write("\b \b".Repeat(placeholder!.Length));
+                    showPlaceholder = false;
+                }
+
                 text += key.KeyChar.ToString();
                 var output = key.KeyChar.ToString();
                 console.Write(secret ? output.Mask(mask) : output, style);

src/Spectre.Console/Prompts/TextPrompt.cs

@@ -89,6 +89,17 @@ public sealed class TextPrompt<T> : IPrompt<T>, IHasCulture
     /// </summary>
     internal DefaultPromptValue<T>? DefaultValue { get; set; }
 
+    /// <summary>
+    /// Gets or sets the placeholder text (displayed when input is empty).
+    /// </summary>
+    public string? Placeholder { get; set; }
+
+    /// <summary>
+    /// Gets or sets the style for the placeholder.
+    /// Defaults to grey if null.
+    /// </summary>
+    public Style? PlaceholderStyle { get; set; }
+
     /// <summary>
     /// Initializes a new instance of the <see cref="TextPrompt{T}"/> class.
     /// </summary>
@@ -130,7 +141,7 @@ public async Task<T> ShowAsync(IAnsiConsole console, CancellationToken cancellat
 
             while (true)
             {
-                var input = await console.ReadLine(promptStyle, IsSecret, Mask, choices, cancellationToken).ConfigureAwait(false);
+                var input = await console.ReadLine(promptStyle, IsSecret, Mask, choices, Placeholder, PlaceholderStyle, cancellationToken).ConfigureAwait(false);
 
                 // Nothing entered?
                 if (string.IsNullOrWhiteSpace(input))

src/Tests/Spectre.Console.Tests/Expectations/Prompts/Text/Placeholder_Shown.Output.verified.txt

@@ -0,0 +1 @@
+Enter your name: ex: Bob       Alice

src/Tests/Spectre.Console.Tests/Expectations/Prompts/Text/Placeholder_Style_Applied.Output.verified.txt

@@ -0,0 +1 @@
+Enter Value: ex: 5     2

src/Tests/Spectre.Console.Tests/Unit/Prompts/TextPromptTests.cs

@@ -410,4 +410,54 @@ public Task Uses_the_specified_choices_style()
         // Then
         return Verifier.Verify(console.Output);
     }
+
+
+    [Fact]
+    [Expectation("Placeholder_Shown")]
+    public Task Should_Display_Placeholder_When_Input_Is_Empty()
+    {
+        // Given
+        var console = new TestConsole
+        {
+            EmitAnsiSequences = false
+        };
+
+        console.Input.PushTextWithEnter("Alice");
+
+        // When
+        var prompt = new TextPrompt<string>("Enter your name:")
+        {
+            Placeholder = "ex: Bob",
+        };
+        console.Prompt(prompt);
+
+        // Then
+        return Verifier.Verify(console.Output);
+    }
+
+    [Fact]
+    [Expectation("Placeholder_Style_Applied")]
+    public Task Should_Use_Specified_Style_For_Placeholder()
+    {
+        // Given
+        var console = new TestConsole
+        {
+            EmitAnsiSequences = true
+        };
+
+        console.Input.PushTextWithEnter("2");
+
+        // When
+        var prompt = new TextPrompt<string>("Enter Value:")
+        {
+            Placeholder = "ex: 5",
+            PlaceholderStyle = Color.Red
+        };
+
+        console.Prompt(prompt);
+
+        // Then
+        return Verifier.Verify(console.Output);
+    }
+
 }