Fix escaping of interpolated arguments in markup

src/Spectre.Console.Tests/Unit/Widgets/MarkupTests.cs

@@ -174,4 +174,51 @@ public void Can_Use_Interpolated_Markup_As_IRenderable()
 └─────────────────┘
 ".NormalizeLineEndings());
     }
-}
+    [Fact]
+    public void MarkupInterpolated_Should_Not_Throw_When_Object_ToString_Contains_Brackets()
+    {
+        // Given
+        var console = new TestConsole();
+        var obj = new CoolThing();
+
+        // When
+        Exception ex = Record.Exception(() => console.MarkupInterpolated($"This is a {obj}"));
+
+        // Then
+        ex.ShouldBeNull();
+        console.Output.NormalizeLineEndings().ShouldBe("This is a This[contains, braces].");
+    }
+
+    [Fact]
+    public void MarkupInterpolated_Should_Preserve_Null_For_Custom_Formatter()
+    {
+        // Given
+        var console = new TestConsole();
+        string? value = null;
+
+        // When
+        Exception ex = Record.Exception(() => console.MarkupInterpolated(new NullAwareFormatProvider(), $"Value: {value}"));
+
+        // Then
+        ex.ShouldBeNull();
+        console.Output.NormalizeLineEndings().ShouldBe("Value: <null>");
+    }
+
+    private class CoolThing
+    {
+        public override string ToString() => "This[contains, braces].";
+    }
+
+    private sealed class NullAwareFormatProvider : IFormatProvider, ICustomFormatter
+    {
+        public object? GetFormat(Type? formatType)
+        {
+            return formatType == typeof(ICustomFormatter) ? this : null;
+        }
+
+        public string Format(string? format, object? arg, IFormatProvider? formatProvider)
+        {
+            return arg is null ? "<null>" : arg.ToString() ?? string.Empty;
+        }
+    }
+}

src/Spectre.Console/Widgets/Markup.cs

@@ -107,7 +107,15 @@ public static string Remove(string text)
 
     internal static string EscapeInterpolated(IFormatProvider provider, FormattableString value)
     {
-        object?[] args = value.GetArguments().Select(arg => arg is string s ? s.EscapeMarkup() : arg).ToArray();
+        object?[] args = value.GetArguments()
+            .Select(arg => arg switch
+            {
+                null => null,
+                string text => text.EscapeMarkup(),
+                IFormattable => arg,
+                _ => arg.ToString()?.EscapeMarkup(),
+            })
+            .ToArray();
         return string.Format(provider, value.Format, args);
     }
-}
+}