apply [StringSyntax( Regex )] to [PatternStringAttribute( string rege…

src/D2L.CodeStyle.Annotations/Contract/PatternStringAttribute.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace D2L.CodeStyle.Annotations.Contract;
 
@@ -9,7 +10,9 @@ namespace D2L.CodeStyle.Annotations.Contract;
 [AttributeUsage( AttributeTargets.Parameter, AllowMultiple = true )]
 public sealed class PatternStringAttribute : Attribute {
 
-	public PatternStringAttribute( string regexPattern ) {
+	public PatternStringAttribute(
+		[StringSyntax( StringSyntaxAttribute.Regex )] string regexPattern
+	) {
 		RegexPattern = regexPattern;
 	}
 

src/D2L.CodeStyle.Annotations/_InternalPolyfills/StringSyntaxAttribute.cs

@@ -0,0 +1,61 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Adapted from https://github.com/dotnet/dotnet/blob/b0f34d51fccc69fd334253924abd8d6853fad7aa/src/runtime/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/StringSyntaxAttribute.cs
+
+namespace System.Diagnostics.CodeAnalysis {
+	/// <summary>Specifies the syntax used in a string.</summary>
+	[AttributeUsage( AttributeTargets.Parameter | AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = false )]
+	internal
+	sealed class StringSyntaxAttribute : Attribute {
+
+		/// <summary>Initializes the <see cref="StringSyntaxAttribute"/> with the identifier of the syntax used.</summary>
+		/// <param name="syntax">The syntax identifier.</param>
+		public StringSyntaxAttribute( string syntax ) {
+			Syntax = syntax;
+			Arguments = [];
+		}
+
+		/// <summary>Gets the identifier of the syntax used.</summary>
+		public string Syntax { get; }
+
+		/// <summary>Optional arguments associated with the specific syntax employed.</summary>
+		public object?[] Arguments { get; }
+
+		/// <summary>The syntax identifier for strings containing composite formats for string formatting.</summary>
+		public const string CompositeFormat = nameof( CompositeFormat );
+
+		/// <summary>The syntax identifier for strings containing date format specifiers.</summary>
+		public const string DateOnlyFormat = nameof( DateOnlyFormat );
+
+		/// <summary>The syntax identifier for strings containing date and time format specifiers.</summary>
+		public const string DateTimeFormat = nameof( DateTimeFormat );
+
+		/// <summary>The syntax identifier for strings containing <see cref="Enum"/> format specifiers.</summary>
+		public const string EnumFormat = nameof( EnumFormat );
+
+		/// <summary>The syntax identifier for strings containing <see cref="Guid"/> format specifiers.</summary>
+		public const string GuidFormat = nameof( GuidFormat );
+
+		/// <summary>The syntax identifier for strings containing JavaScript Object Notation (JSON).</summary>
+		public const string Json = nameof( Json );
+
+		/// <summary>The syntax identifier for strings containing numeric format specifiers.</summary>
+		public const string NumericFormat = nameof( NumericFormat );
+
+		/// <summary>The syntax identifier for strings containing regular expressions.</summary>
+		public const string Regex = nameof( Regex );
+
+		/// <summary>The syntax identifier for strings containing time format specifiers.</summary>
+		public const string TimeOnlyFormat = nameof( TimeOnlyFormat );
+
+		/// <summary>The syntax identifier for strings containing <see cref="TimeSpan"/> format specifiers.</summary>
+		public const string TimeSpanFormat = nameof( TimeSpanFormat );
+
+		/// <summary>The syntax identifier for strings containing URIs.</summary>
+		public const string Uri = nameof( Uri );
+
+		/// <summary>The syntax identifier for strings containing XML.</summary>
+		public const string Xml = nameof( Xml );
+	}
+}