Abort formatting exception

src/SmartFormat.Tests/Core/FormatterTests.cs

@@ -4,6 +4,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using NUnit.Framework;
+using SmartFormat.Core.Extensions;
 using SmartFormat.Core.Formatting;
 using SmartFormat.Core.Output;
 using SmartFormat.Core.Settings;
@@ -344,4 +345,46 @@ public void Parallel_Smart_Format()
         // Restore to saved value
         ThreadSafeMode.SwitchTo(savedMode);
     }
-}
+
+    public class AbortFormatSource : ISource
+    {
+        public string? Message { get; set; }
+
+        public bool TryEvaluateSelector(ISelectorInfo selectorInfo)
+        {
+            if (selectorInfo.SelectorText == "abort")
+            {
+                if (Message == null)
+                    throw new AbortFormattingException();
+                throw new AbortFormattingException(Message);
+            }
+            return false;
+        }
+    }
+
+    [TestCase("Some text {abort}", "Some text ")]
+    [TestCase("Some text {1.abort}", "Some text ")]
+    [TestCase("Some text {0.abort.some.selector}", "Some text ")]
+    [TestCase("Some text {abort.some.selector:plural:Apple|{} Apples}", "Some text ")]
+    public void AbortFormattingException_PreventsFurtherProcessing(string text, string expected)
+    {
+        var formatter = GetSimpleFormatter();
+        formatter.AddExtensions(new AbortFormatSource());
+
+        var actual = formatter.Format(text, 1, 2);
+        Assert.That(actual, Is.EqualTo(expected));
+    }
+
+    [TestCase("Some text {abort}", "", "Some text ")]
+    [TestCase("Some text {1.abort}", "Message", "Some text Message")]
+    [TestCase("Some text {0.abort.some.selector}", "A Message", "Some text A Message")]
+    [TestCase("Some text {abort.some.selector:plural:Apple|{} Apples}", "<Error>", "Some text <Error>")]
+    public void AbortFormattingException_PreventsFurtherProcessingAndIncludesMessage(string text, string message, string expected)
+    {
+        var formatter = GetSimpleFormatter();
+        formatter.AddExtensions(new AbortFormatSource { Message = message });
+
+        var actual = formatter.Format(text, 1, 2);
+        Assert.That(actual, Is.EqualTo(expected));
+    }
+}

src/SmartFormat/Core/Formatting/AbortFormattingException.cs

@@ -0,0 +1,33 @@
+// 
+// Copyright SmartFormat Project maintainers and contributors.
+// Licensed under the MIT license.
+
+using System;
+using SmartFormat.Core.Extensions;
+
+namespace SmartFormat.Core.Formatting;
+
+/// <summary>
+/// An exception designed to halt further processing for a specific format item.
+/// This exception can be raised from an <see cref="ISource"/> to prevent additional processing,
+/// particularly in scenarios where the data's state is not yet prepared or deemed valid.
+/// </summary>
+public class AbortFormattingException : Exception
+{
+    /// <summary>
+    /// Creates a new instance of <see cref="AbortFormattingException"/>.
+    /// </summary>
+    /// <param name="text">Optional text to be used in the output string.</param>
+    public AbortFormattingException(string text)
+    {
+        Text = text;
+    }
+
+    ///<inheritdoc/>
+    public AbortFormattingException() { }
+
+    /// <summary>
+    /// A message to be used in the output string.
+    /// </summary>
+    public string? Text { get; }
+}

src/SmartFormat/SmartFormatter.cs

@@ -387,6 +387,12 @@ public void Format(FormattingInfo formattingInfo)
             {
                 EvaluateSelectors(childFormattingInfo);
             }
+            catch (AbortFormattingException ex)
+            {
+                if (ex.Text != null)
+                    formattingInfo.Write(ex.Text);
+                continue;
+            }
             catch (Exception ex)
             {
                 // An error occurred while evaluation selectors