Add SZArrayHelper and Unsafe.As<T> (#257)

Author: josesimoes

nanoFramework.CoreLibrary/CoreLibrary.nfproj

@@ -74,6 +74,7 @@
     <Compile Include="System\Collections\Generic\IEnumerator.cs" />
     <Compile Include="System\Diagnostics\StackTraceHiddenAttribute.cs" />
     <Compile Include="System\Nullable.cs" />
+    <Compile Include="System\Runtime\CompilerServices\Unsafe.cs" />
     <Compile Include="System\Runtime\InteropServices\InAttribute .cs" />
     <Compile Include="System\Diagnostics\NativeProfiledAttribute.cs" />
     <Compile Include="System\PlatformNotSupportedException.cs" />
@@ -262,4 +263,4 @@
   <Import Project="..\packages\Microsoft.SourceLink.Common.1.1.1\build\Microsoft.SourceLink.Common.targets" Condition="Exists('..\packages\Microsoft.SourceLink.Common.1.1.1\build\Microsoft.SourceLink.Common.targets')" />
   <Import Project="..\packages\Microsoft.SourceLink.GitHub.1.1.1\build\Microsoft.SourceLink.GitHub.targets" Condition="Exists('..\packages\Microsoft.SourceLink.GitHub.1.1.1\build\Microsoft.SourceLink.GitHub.targets')" />
   <Import Project="..\packages\Nerdbank.GitVersioning.3.7.115\build\Nerdbank.GitVersioning.targets" Condition="Exists('..\packages\Nerdbank.GitVersioning.3.7.115\build\Nerdbank.GitVersioning.targets')" />
-</Project>
+</Project>

nanoFramework.CoreLibrary/System/Array.cs

@@ -3,6 +3,10 @@
 
 using System.Collections;
 using System.Runtime.CompilerServices;
+#if NANOCLR_REFLECTION
+using System.Collections.Generic;
+using System.Diagnostics;
+#endif // NANOCLR_REFLECTION
 
 namespace System
 {
@@ -429,5 +433,153 @@ public void Reset()
                 _index = _startIndex - 1;
             }
         }
+
+#if NANOCLR_REFLECTION
+#pragma warning disable CA1822 // Mark members as static
+        //----------------------------------------------------------------------------------------
+        // ! READ THIS BEFORE YOU WORK ON THIS CLASS.
+        //
+        // The methods on this class must be written VERY carefully to avoid introducing security holes.
+        // That's because they are invoked with special "this"! The "this" object
+        // for all of these methods are not SZArrayHelper objects. Rather, they are of type U[]
+        // where U[] is castable to T[]. No actual SZArrayHelper object is ever instantiated. Thus, you will
+        // see a lot of expressions that cast "this" "T[]".
+        //
+        // This class is needed to allow an SZ array of type T[] to expose IList<T>,
+        // IList<T.BaseType>, etc., etc. all the way up to IList<Object>. When the following call is
+        // made:
+        //
+        //   ((IList<T>) (new U[n])).SomeIListMethod()
+        //
+        // the interface stub dispatcher treats this as a special case, loads up SZArrayHelper,
+        // finds the corresponding generic method (matched simply by method name), instantiates
+        // it for type <T> and executes it.
+        //
+        // The "T" will reflect the interface used to invoke the method. The actual runtime "this" will be
+        // array that is castable to "T[]" (i.e. for primitives and valuetypes, it will be exactly
+        // "T[]" - for orefs, it may be a "U[]" where U derives from T.)
+        //----------------------------------------------------------------------------------------
+        internal sealed class SZArrayHelper
+        {
+            // It is never legal to instantiate this class.
+            private SZArrayHelper()
+            {
+                Debug.Assert(false, "Hey! How'd I get here?");
+            }
+
+            internal IEnumerator<T> GetEnumerator<T>()
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+                T[] @this = Unsafe.As<T[]>(this);
+                int length = @this.Length;
+                return length == 0 ? SZGenericArrayEnumerator<T>.Empty : new SZGenericArrayEnumerator<T>(@this, length);
+            }
+
+            private void CopyTo<T>(T[] array, int index)
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+
+                T[] @this = Unsafe.As<T[]>(this);
+                Array.Copy(@this, 0, array, index, @this.Length);
+            }
+
+            internal int get_Count<T>()
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+                T[] @this = Unsafe.As<T[]>(this);
+                return @this.Length;
+            }
+
+            internal T get_Item<T>(int index)
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+
+                T[] @this = Unsafe.As<T[]>(this);
+                if ((uint)index >= (uint)@this.Length)
+                {
+#pragma warning disable S3928 // Parameter names used into ArgumentException constructors should match an existing one 
+                    throw new ArgumentOutOfRangeException();
+#pragma warning restore S3928 // Parameter names used into ArgumentException constructors should match an existing one 
+                }
+
+                return @this[index];
+            }
+
+            internal void set_Item<T>(int index, T value)
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+                T[] @this = Unsafe.As<T[]>(this);
+                if ((uint)index >= (uint)@this.Length)
+                {
+#pragma warning disable S3928 // Parameter names used into ArgumentException constructors should match an existing one 
+                    throw new ArgumentOutOfRangeException();
+#pragma warning restore S3928 // Parameter names used into ArgumentException constructors should match an existing one 
+                }
+
+                @this[index] = value;
+            }
+
+            private void Add<T>(T _)
+            {
+                // Not meaningful for arrays.
+                throw new NotSupportedException();
+            }
+
+            private bool Contains<T>(T value)
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+                T[] @this = Unsafe.As<T[]>(this);
+                return Array.IndexOf(@this, value, 0, @this.Length) >= 0;
+            }
+
+            private bool get_IsReadOnly<T>()
+            {
+                return true;
+            }
+
+            private void Clear<T>()
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+
+                throw new NotSupportedException();
+            }
+
+            private int IndexOf<T>(T value)
+            {
+                // ! Warning: "this" is an array, not an SZArrayHelper. See comments above
+                // ! or you may introduce a security hole!
+                T[] @this = Unsafe.As<T[]>(this);
+                return Array.IndexOf(@this, value, 0, @this.Length);
+            }
+
+            private void Insert<T>(int _, T _1)
+            {
+                // Not meaningful for arrays
+                throw new NotSupportedException();
+            }
+
+            private bool Remove<T>(T _)
+            {
+                // Not meaningful for arrays
+                throw new NotSupportedException();
+                return default;
+            }
+
+            private void RemoveAt<T>(int _)
+            {
+                // Not meaningful for arrays
+                throw new NotSupportedException();
+            }
+        }
+#pragma warning restore CA1822
+
+#endif
     }
 }

nanoFramework.CoreLibrary/System/Runtime/CompilerServices/Unsafe.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if NANOCLR_REFLECTION
+#nullable enable
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// Contains generic, low-level functionality for manipulating pointers.
+    /// </summary>
+    public static unsafe partial class Unsafe
+    {
+        /// <summary>
+        /// Casts the given object to the specified type, performs no dynamic type checking.
+        /// </summary>
+        /// <typeparam name="T">The target reference type. The return value will be of this type.</typeparam>
+        [MethodImpl(MethodImplOptions.InternalCall)]
+        public static extern T? As<T>(object? o) where T : class?;
+    }
+}
+
+#endif