Update /// comments for new InteropServices APIs

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Architecture.cs

@@ -3,16 +3,49 @@
 
 namespace System.Runtime.InteropServices
 {
+    /// <summary>
+    /// Indicates the processor architecture.
+    /// </summary>
     public enum Architecture
     {
+        /// <summary>
+        /// An Intel-based 32-bit processor architecture.
+        /// </summary>
         X86,
+        /// <summary>
+        /// An Intel-based 64-bit processor architecture.
+        /// </summary>
         X64,
+        /// <summary>
+        /// A 32-bit ARM processor architecture.
+        /// </summary>
         Arm,
+        /// <summary>
+        /// A 64-bit ARM processor architecture.
+        /// </summary>
         Arm64,
+        /// <summary>
+        /// The WebAssembly platform.
+        /// </summary>
         Wasm,
+        /// <summary>
+        /// A S390x platform architecture.
+        /// </summary>
         S390x,
+        /// <summary>
+        /// A LoongArch64 processor architecture.
+        /// </summary>
         LoongArch64,
+        /// <summary>
+        /// A 32-bit ARMv6 processor architecture.
+        /// </summary>
+        /// <remarks>
+        /// This value indicates ARMv6 base instructions, VFPv2 floating point support and registers, hard-float ABI, and no compact instruction set.
+        /// </remarks>
         Armv6,
+        /// <summary>
+        /// A PowerPC 64-bit (little-endian) processor architecture.
+        /// </summary>
         Ppc64le,
     }
 }

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/ArrayMarshaller.cs

@@ -22,6 +22,12 @@ namespace System.Runtime.InteropServices.Marshalling
     public static unsafe class ArrayMarshaller<T, TUnmanagedElement>
         where TUnmanagedElement : unmanaged
     {
+        /// <summary>
+        /// Allocates memory for the unmanaged representation of the array.
+        /// </summary>
+        /// <param name="managed">The managed array</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The unmanaged pointer to the allocated memory</returns>
         public static TUnmanagedElement* AllocateContainerForUnmanagedElements(T[]? managed, out int numElements)
         {
             if (managed is null)
@@ -37,12 +43,29 @@ public static unsafe class ArrayMarshaller<T, TUnmanagedElement>
             return (TUnmanagedElement*)Marshal.AllocCoTaskMem(spaceToAllocate);
         }
 
+        /// <summary>
+        /// Gets a source for the managed elements in the array.
+        /// </summary>
+        /// <param name="managed">The managed array</param>
+        /// <returns>The <see cref="ReadOnlySpan{T}"/> containing the managed elements to marshal</returns>
         public static ReadOnlySpan<T> GetManagedValuesSource(T[]? managed)
             => managed;
 
+        /// <summary>
+        /// Gets a destination for the unmanaged elements in the array.
+        /// </summary>
+        /// <param name="unmanaged">The unmanaged allocation</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The <see cref="Span{TUnmanagedElement}"/> of unmanaged elements</returns>
         public static Span<TUnmanagedElement> GetUnmanagedValuesDestination(TUnmanagedElement* unmanaged, int numElements)
             => new Span<TUnmanagedElement>(unmanaged, numElements);
 
+        /// <summary>
+        /// Allocates memory for the managed representation of the array.
+        /// </summary>
+        /// <param name="unmanaged">The unmanaged array</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The managed array</returns>
         public static T[]? AllocateContainerForManagedElements(TUnmanagedElement* unmanaged, int numElements)
         {
             if (unmanaged is null)
@@ -51,17 +74,41 @@ public static Span<TUnmanagedElement> GetUnmanagedValuesDestination(TUnmanagedEl
             return new T[numElements];
         }
 
+        /// <summary>
+        /// Gets a destination for the managed elements in the array.
+        /// </summary>
+        /// <param name="managed">The managed array</param>
+        /// <returns>The <see cref="Span{T}"/> of managed elements</returns>
         public static Span<T> GetManagedValuesDestination(T[]? managed)
             => managed;
 
+        /// <summary>
+        /// Gets a source for the unmanaged elements in the array.
+        /// </summary>
+        /// <param name="unmanagedValue">The unmanaged array</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The <see cref="ReadOnlySpan{TUnmanagedElement}"/> containing the unmanaged elements to marshal</returns>
         public static ReadOnlySpan<TUnmanagedElement> GetUnmanagedValuesSource(TUnmanagedElement* unmanagedValue, int numElements)
             => new ReadOnlySpan<TUnmanagedElement>(unmanagedValue, numElements);
 
+        /// <summary>
+        /// Frees memory for the unmanaged array
+        /// </summary>
+        /// <param name="unmanaged">Unmanaged array</param>
         public static void Free(TUnmanagedElement* unmanaged)
             => Marshal.FreeCoTaskMem((IntPtr)unmanaged);
 
+        /// <summary>
+        /// Marshaller for marshalling a array from managed to unmanaged.
+        /// </summary>
         public ref struct ManagedToUnmanagedIn
         {
+            /// <summary>
+            /// Requested caller-allocated buffer size.
+            /// </summary>
+            /// <remarks>
+            /// Represents a potential optimization for the marshaller.
+            /// </remarks>
             // We'll keep the buffer size at a maximum of 200 bytes to avoid overflowing the stack.
             public static int BufferSize { get; } = 0x200 / sizeof(TUnmanagedElement);
 
@@ -134,6 +181,11 @@ public void Free()
                 NativeMemory.Free(_allocatedMemory);
             }
 
+            /// <summary>
+            /// Gets a pinnable reference to the managed span to a pointer to pass directly to unmanaged code.
+            /// </summary>
+            /// <param name="array">The managed array.</param>
+            /// <returns>The reference that can be pinned and directly passed to unmanaged code.</returns>
             public static ref T GetPinnableReference(T[]? array)
             {
                 if (array is null)

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/PointerArrayMarshaller.cs

@@ -23,6 +23,12 @@ public static unsafe class PointerArrayMarshaller<T, TUnmanagedElement>
         where T : unmanaged
         where TUnmanagedElement : unmanaged
     {
+        /// <summary>
+        /// Allocates memory for the unmanaged representation of the array.
+        /// </summary>
+        /// <param name="managed">The managed array to marshal</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The unmanaged pointer to the allocated memory</returns>
         public static TUnmanagedElement* AllocateContainerForUnmanagedElements(T*[]? managed, out int numElements)
         {
             if (managed is null)
@@ -38,12 +44,29 @@ public static unsafe class PointerArrayMarshaller<T, TUnmanagedElement>
             return (TUnmanagedElement*)Marshal.AllocCoTaskMem(spaceToAllocate);
         }
 
+        /// <summary>
+        /// Gets a source for the managed elements in the array.
+        /// </summary>
+        /// <param name="managed">The managed array</param>
+        /// <returns>The <see cref="ReadOnlySpan{IntPtr}"/> containing the managed elements to marshal</returns>
         public static ReadOnlySpan<IntPtr> GetManagedValuesSource(T*[]? managed)
             => Unsafe.As<IntPtr[]>(managed);
 
+        /// <summary>
+        /// Gets a destination for the unmanaged elements in the array.
+        /// </summary>
+        /// <param name="unmanaged">The unmanaged allocation</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The <see cref="Span{TUnmanagedElement}"/> of unmanaged elements</returns>
         public static Span<TUnmanagedElement> GetUnmanagedValuesDestination(TUnmanagedElement* unmanaged, int numElements)
             => new Span<TUnmanagedElement>(unmanaged, numElements);
 
+        /// <summary>
+        /// Allocates memory for the managed representation of the array.
+        /// </summary>
+        /// <param name="unmanaged">The unmanaged array</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The managed array</returns>
         public static T*[]? AllocateContainerForManagedElements(TUnmanagedElement* unmanaged, int numElements)
         {
             if (unmanaged is null)
@@ -52,17 +75,42 @@ public static Span<TUnmanagedElement> GetUnmanagedValuesDestination(TUnmanagedEl
             return new T*[numElements];
         }
 
+        /// <summary>
+        /// Gets a destination for the managed elements in the array.
+        /// </summary>
+        /// <param name="managed">The managed array</param>
+        /// <returns>The <see cref="Span{T}"/> of managed elements</returns>
         public static Span<IntPtr> GetManagedValuesDestination(T*[]? managed)
             => Unsafe.As<IntPtr[]>(managed);
 
+        /// <summary>
+        /// Gets a source for the unmanaged elements in the array.
+        /// </summary>
+        /// <param name="unmanagedValue">The unmanaged array</param>
+        /// <param name="numElements">The unmanaged element count</param>
+        /// <returns>The <see cref="ReadOnlySpan{TUnmanagedElement}"/> containing the unmanaged elements to marshal</returns>
         public static ReadOnlySpan<TUnmanagedElement> GetUnmanagedValuesSource(TUnmanagedElement* unmanagedValue, int numElements)
             => new ReadOnlySpan<TUnmanagedElement>(unmanagedValue, numElements);
 
+        /// <summary>
+        /// Frees memory for the unmanaged array
+        /// </summary>
+        /// <param name="unmanaged">Unmanaged array</param>
         public static void Free(TUnmanagedElement* unmanaged)
             => Marshal.FreeCoTaskMem((IntPtr)unmanaged);
 
+        /// <summary>
+        /// Marshaller for marshalling a array from managed to unmanaged.
+        /// </summary>
         public ref struct ManagedToUnmanagedIn
         {
+            /// <summary>
+            /// Requested caller-allocated buffer size.
+            /// </summary>
+            /// <remarks>
+            /// Represents a potential optimization for the marshaller.
+            /// </remarks>
+            // We'll keep the buffer size at a maximum of 200 bytes to avoid overflowing the stack.
             public static int BufferSize => 0x200 / sizeof(TUnmanagedElement);
 
             private T*[]? _managedArray;
@@ -134,6 +182,11 @@ public void Free()
                 NativeMemory.Free(_allocatedMemory);
             }
 
+            /// <summary>
+            /// Gets a pinnable reference to the managed span to a pointer to pass directly to unmanaged code.
+            /// </summary>
+            /// <param name="array">The managed array.</param>
+            /// <returns>The reference that can be pinned and directly passed to unmanaged code.</returns>
             public static ref byte GetPinnableReference(T*[]? array)
             {
                 if (array is null)

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/SpanMarshaller.cs

@@ -180,6 +180,11 @@ public void Free()
                 NativeMemory.Free(_allocatedMemory);
             }
 
+            /// <summary>
+            /// Pin the managed span to a pointer to pass directly to unmanaged code.
+            /// </summary>
+            /// <param name="managed">The managed span.</param>
+            /// <returns>A reference that can be pinned and directly passed to unmanaged code.</returns>
             public static ref T GetPinnableReference(Span<T> managed)
             {
                 return ref MemoryMarshal.GetReference(managed);

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/StringMarshalling.cs

@@ -20,8 +20,17 @@ namespace System.Runtime.InteropServices
 #endif
     enum StringMarshalling
     {
+        /// <summary>
+        /// Indicates the user is suppling a specific marshaller in <see cref="LibraryImportAttribute.StringMarshallingCustomType"/>.
+        /// </summary>
         Custom = 0,
-        Utf8,   // UTF-8
-        Utf16,  // UTF-16, machine-endian
+        /// <summary>
+        /// Use the platform-provided UTF-8 marshaller.
+        /// </summary>
+        Utf8,
+        /// <summary>
+        /// Use the platform-provided UTF-16 marshaller.
+        /// </summary>
+        Utf16,
     }
 }