Annotating Regex library for Native Aot apps

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.cs

@@ -74,6 +74,8 @@ internal Regex(string pattern, CultureInfo? culture)
             // if no options are ever used.
         }
 
+        [UnconditionalSuppressMessage("AotAnalysis", "IL3050:RequiresDynamicCode",
+            Justification = "Compiled Regex is only used when RuntimeFeature.IsDynamicCodeCompiled is true. Workaround https://github.com/dotnet/linker/issues/2715.")]
         internal Regex(string pattern, RegexOptions options, TimeSpan matchTimeout, CultureInfo? culture)
         {
             // Validate arguments.
@@ -201,6 +203,7 @@ protected IDictionary? CapNames
         /// Regex constructor, we don't load RegexCompiler and its reflection classes when
         /// instantiating a non-compiled regex.
         /// </summary>
+        [RequiresDynamicCode("Compiling a RegEx requires dynamic code.")]
         [MethodImpl(MethodImplOptions.NoInlining)]
         private static RegexRunnerFactory? Compile(string pattern, RegexTree regexTree, RegexOptions options, bool hasTimeout) =>
             RegexCompiler.Compile(pattern, regexTree, options, hasTimeout);

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs

@@ -15,6 +15,7 @@ namespace System.Text.RegularExpressions
     /// <summary>
     /// RegexCompiler translates a block of RegexCode to MSIL, and creates a subclass of the RegexRunner type.
     /// </summary>
+    [RequiresDynamicCode("Compiling a RegEx requires dynamic code.")]
     internal abstract class RegexCompiler
     {
         private static readonly FieldInfo s_runtextstartField = RegexRunnerField("runtextstart");

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexLWCGCompiler.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using System.Reflection;
 using System.Reflection.Emit;
@@ -30,6 +31,7 @@ internal sealed class RegexLWCGCompiler : RegexCompiler
         private static int s_regexCount;
 
         /// <summary>The top-level driver. Initializes everything then calls the Generate* methods.</summary>
+        [RequiresDynamicCode("Compiling a RegEx requires dynamic code.")]
         public RegexRunnerFactory? FactoryInstanceFromCode(string pattern, RegexTree regexTree, RegexOptions options, bool hasTimeout)
         {
             if (!regexTree.Root.SupportsCompilation(out _))
@@ -65,6 +67,7 @@ internal sealed class RegexLWCGCompiler : RegexCompiler
         }
 
         /// <summary>Begins the definition of a new method (no args) with a specified return value.</summary>
+        [RequiresDynamicCode("Compiling a RegEx requires dynamic code.")]
         private DynamicMethod DefineDynamicMethod(string methname, Type? returntype, Type hostType, Type[] paramTypes)
         {
             // We're claiming that these are static methods, but really they are instance methods.