Add interface IFormattingExtensionsToggle to skip formatting (#436)

Author: axunonb

src/SmartFormat.Tests/Extensions/DefaultSourceTests.cs

@@ -31,4 +31,4 @@ public void Call_With_Numeric_Placeholder_Should_Succeed()
         Assert.That(code:() => { result = smart.Format("{0}", 999); }, Throws.Nothing);
         Assert.That(result, Is.EqualTo("999"));
     }
-}
+}

src/SmartFormat.Tests/Extensions/NoFormattingSourceTests.cs

@@ -0,0 +1,44 @@
+using NUnit.Framework;
+using SmartFormat.Core.Extensions;
+using SmartFormat.Core.Formatting;
+using SmartFormat.Extensions;
+
+namespace SmartFormat.Tests.Extensions;
+
+[TestFixture]
+public class NoFormattingSourceTests
+{
+    [Test]
+    public void Use_of_ToggleFormattingExtensions()
+    {
+        var smart = new SmartFormatter();
+        smart.AddExtensions(new NoFormattingSource());
+        smart.AddExtensions(new DefaultFormatter());
+
+        Assert.That(smart.Format("{0}", 999), Is.EqualTo("No formatting"));
+    }
+
+    public class NoFormattingSource : ISource
+    {
+        public bool TryEvaluateSelector(ISelectorInfo selectorInfo)
+        {
+            // Split test for IFormattingExtensionsToggle and FormattingInfo
+            // for clarity. This is not necessary in production code.
+
+            // Disable all formatting extensions
+            if (selectorInfo is IFormattingExtensionsToggle toggle)
+            {
+                toggle.DisableFormattingExtensions = true;
+            }
+
+            if (selectorInfo is FormattingInfo fi)
+            {
+                // Write a note or result directly to the output
+                fi.Write("No formatting");
+            }
+
+            selectorInfo.Result = selectorInfo.CurrentValue;
+            return true;
+        }
+    }
+}

src/SmartFormat.Tests/Extensions/ValueTupleSourceTests.cs

@@ -131,6 +131,6 @@ private class PureSelectorInfo : ISelectorInfo
         public string SelectorOperator { get; } = string.Empty;
         public object? Result { get; set; }
         public Placeholder? Placeholder { get; }
-        public FormatDetails FormatDetails { get; } = (FormatDetails) null!; // dummy
+        public FormatDetails FormatDetails { get; } = null!; // dummy
     }
 }

src/SmartFormat/Core/Extensions/IFormattingExtensionsToggler.cs

@@ -0,0 +1,27 @@
+// 
+// Copyright SmartFormat Project maintainers and contributors.
+// Licensed under the MIT license.
+
+using System;
+
+namespace SmartFormat.Core.Extensions;
+
+/// <summary>
+/// Represents a toggle for enabling or disabling <see cref="IFormatter"/> extensions.
+/// This interface is primarily used by <see cref="ISource"/> extensions
+/// that receive it as part of the <see cref="ISelectorInfo"/> parameter.
+/// </summary>
+public interface IFormattingExtensionsToggle
+{
+    // This interface should become part of ISelectorInfo in the future.
+
+    /// <summary>
+    /// Gets or sets a value indicating whether the <see cref="IFormatter"/> extensions are enabled.
+    /// The value should be <see langword="false"/> (default), unless the <see cref="ISource"/> extension
+    /// found a value in <seealso cref="ISource.TryEvaluateSelector"/> where default formatting cannot reasonably be done.
+    /// <br/>
+    /// In this case the <see cref="ISource"/> may directly write some output using <see cref="IFormattingInfo.Write(ReadOnlySpan{char})"/>,
+    /// or produce no output at all.
+    /// </summary>
+    public bool DisableFormattingExtensions { get; set; }
+}

src/SmartFormat/Core/Extensions/ISource.cs

@@ -2,6 +2,7 @@
 // Copyright SmartFormat Project maintainers and contributors.
 // Licensed under the MIT license.
 
+using SmartFormat.Core.Formatting;
 using SmartFormat.Core.Parsing;
 
 namespace SmartFormat.Core.Extensions;
@@ -14,7 +15,8 @@ public interface ISource
     /// <summary>
     /// Evaluates the <see cref="Selector" /> based on the <see cref="ISelectorInfo.CurrentValue" />.
     /// </summary>
-    /// <param name="selectorInfo"></param>
+    /// <param name="selectorInfo">The information about the selector being evaluated.<br/>
+    /// Note: This can be casted to <seealso cref="FormattingInfo"/>, which also implements <seealso cref="IFormattingExtensionsToggle"/>.</param>
     /// <returns>If the <see cref="Selector"/> could be evaluated,
     /// the <see cref="ISelectorInfo.Result" /> will be set and <see langword="true"/> will be returned.
     /// </returns>

src/SmartFormat/Core/Formatting/FormattingInfo.cs

@@ -3,7 +3,6 @@
 // Licensed under the MIT license.
 
 using System;
-using System.Buffers;
 using System.Collections.Generic;
 using SmartFormat.Core.Extensions;
 using SmartFormat.Core.Output;
@@ -17,7 +16,7 @@ namespace SmartFormat.Core.Formatting;
 /// <summary>
 /// The class contains the fields and methods which are necessary for formatting.
 /// </summary>
-public class FormattingInfo : IFormattingInfo, ISelectorInfo
+public class FormattingInfo : IFormattingInfo, ISelectorInfo, IFormattingExtensionsToggle
 {
     /// <summary>
     /// CTOR for object pooling.
@@ -52,6 +51,7 @@ public FormattingInfo Initialize(FormattingInfo? parent, FormatDetails formatDet
         CurrentValue = currentValue;
         FormatDetails = formatDetails;
         Format = format;
+        DisableFormattingExtensions = false;
         // inherit alignment
         if (parent != null) Alignment = parent.Alignment;
         else if (format.ParentPlaceholder != null) Alignment = format.ParentPlaceholder.Alignment;
@@ -73,6 +73,7 @@ public FormattingInfo Initialize(FormattingInfo? parent, FormatDetails formatDet
         FormatDetails = formatDetails;
         Placeholder = placeholder;
         Format = placeholder.Format;
+        DisableFormattingExtensions = false;
         CurrentValue = currentValue;
         // inherit alignment
         Alignment = placeholder.Alignment;
@@ -94,6 +95,7 @@ public void ReturnToPool()
         Alignment = 0;
 
         Format = null;
+        DisableFormattingExtensions = false;
         CurrentValue = null;
 
         // Children can safely be returned
@@ -304,6 +306,9 @@ public FormattingException FormattingException(string issue, FormatItem? problem
     /// </summary>
     public object? Result { get; set; }
 
+    /// <inheritdoc />
+    public bool DisableFormattingExtensions { get; set; }
+
     /// <summary>
     /// Creates a child <see cref="FormattingInfo"/> from the current <see cref="FormattingInfo"/> instance for a <see cref="Parsing.Format"/>.
     /// </summary>

src/SmartFormat/Core/Formatting/ISelectorInfo.cs

@@ -29,7 +29,7 @@ public interface ISelectorInfo
     string SelectorText { get; }
 
     /// <summary>
-    /// The index of the selector in a multi-part selector.
+    /// The index of the selector in a multipart selector.
     /// Example: {Person.Birthday.Year} has 3 selectors,
     /// and Year has a SelectorIndex of 2.
     /// </summary>

src/SmartFormat/Evaluator.cs

@@ -6,7 +6,6 @@
 using System;
 using SmartFormat.Core.Extensions;
 using SmartFormat.Core.Formatting;
-using SmartFormat.Core.Output;
 using SmartFormat.Core.Parsing;
 using SmartFormat.Core.Settings;
 using SmartFormat.Pooling.SmartPools;
@@ -225,6 +224,8 @@ private bool SkipThisSelector(Selector selector)
     /// <exception cref="FormattingException"></exception>
     private void InvokeFormatters(FormattingInfo formattingInfo)
     {
+        if (formattingInfo.DisableFormattingExtensions) return;
+
         var placeholder = formattingInfo.Placeholder!;
 
         try