Add polyfills for RandomNumberGenerator class and Fill(Span<byte>) method

PolyShim.Tests/NetCore21/RandomNumberGeneratorTests.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Security.Cryptography;
+using FluentAssertions;
+using Xunit;
+
+namespace PolyShim.Tests.NetCore21;
+
+public class RandomNumberGeneratorTests
+{
+    [Fact]
+    public void Fill_Span_Test()
+    {
+        // Arrange
+        var span = new Span<byte>(new byte[16]);
+
+        // Act
+        RandomNumberGenerator.Fill(span);
+
+        // Assert
+        // Verify that not all bytes are zero (cryptographic RNG should produce non-zero data).
+        // Note: Theoretically, a crypto RNG could produce all zeros (probability: 2^-128),
+        // but this is astronomically unlikely in practice.
+        span.ToArray().Should().Contain(b => b != 0);
+    }
+
+    [Fact]
+    public void Fill_EmptySpan_Test()
+    {
+        // Arrange
+        var span = new Span<byte>();
+
+        // Act & Assert
+        // Should not throw and should return immediately
+        RandomNumberGenerator.Fill(span);
+    }
+}

PolyShim/NetCore21/RandomNumberGenerator.cs

@@ -0,0 +1,46 @@
+#if (NETCOREAPP && !NETCOREAPP2_1_OR_GREATER) || (NETFRAMEWORK) || (NETSTANDARD && !NETSTANDARD2_1_OR_GREATER)
+#nullable enable
+// ReSharper disable RedundantUsingDirective
+// ReSharper disable CheckNamespace
+// ReSharper disable InconsistentNaming
+// ReSharper disable PartialTypeWithSinglePart
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+#if !NETSTANDARD || NETSTANDARD1_3_OR_GREATER
+using System.Security.Cryptography;
+
+[ExcludeFromCodeCoverage]
+internal static class MemberPolyfills_NetCore21_RandomNumberGenerator
+{
+    extension(RandomNumberGenerator)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.fill
+        public static void Fill(Span<byte> data)
+        {
+            // Fast-path for empty spans to avoid unnecessary allocations
+            if (data.Length == 0)
+                return;
+
+            var buffer = new byte[data.Length];
+#if NET35
+            var rng = RandomNumberGenerator.Create();
+            try
+            {
+                rng.GetBytes(buffer);
+                buffer.CopyTo(data);
+            }
+            finally
+            {
+                ((IDisposable)rng).Dispose();
+            }
+#else
+            using var rng = RandomNumberGenerator.Create();
+            rng.GetBytes(buffer);
+            buffer.CopyTo(data);
+#endif
+        }
+    }
+}
+#endif
+#endif

PolyShim/Signatures.md

@@ -1,8 +1,8 @@
 # Signatures
 
-- **Total:** 340
+- **Total:** 341
 - **Types:** 74
-- **Members:** 266
+- **Members:** 267
 
 ___
 
@@ -275,6 +275,8 @@ ___
   - [`T[] GetItems<T>(T[], int)`](https://learn.microsoft.com/dotnet/api/system.random.getitems#system-random-getitems-1(-0()-system-int32)) <sup><sub>.NET 8.0</sub></sup>
   - [`void NextBytes(Span<byte>)`](https://learn.microsoft.com/dotnet/api/system.random.nextbytes#system-random-nextbytes(system-span((system-byte)))) <sup><sub>.NET Core 2.1</sub></sup>
   - [`void Shuffle<T>(T[])`](https://learn.microsoft.com/dotnet/api/system.random.shuffle#system-random-shuffle-1(-0())) <sup><sub>.NET 8.0</sub></sup>
+- `RandomNumberGenerator`
+  - [`void Fill(Span<byte>)`](https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.fill) <sup><sub>.NET Core 2.1</sub></sup>
 - `Range`
   - [**[struct]**](https://learn.microsoft.com/dotnet/api/system.range) <sup><sub>.NET Core 3.0</sub></sup>
 - `ReadOnlyMemory<T>`