Move vendored ReadOnlySpan<T>, Span<T> et. al. to System namespace (#8476)

## Summary of changes

Updates the System.Memory vendoring code to move types like
`ReadOnlySpan<T>`, `Span<T>` into `System` instead of
`Datadog.Trace.VendoredMicrosoftCode.System`

## Reason for change

The compiler has various functionality that relies on the `Span<T>` (and
`ReadOnlySpan<T>`) being available in the `System` namespace. By making
this change, we get the advantage of those types being available.

A separate PR will actually update code to use those types, except where
changes were required to make it compile in this PR.

## Implementation details

Update the vendoring code to stop changing the namespace.

## Test coverage

This is the test, if the tests pass, we should be fine.

## Other details


Depends on a stack updating our vendored system code

- #8391
- #8454
- #8455
- #8459
- #8461
- #8469

Author: andrewlock

tracer/build/_build/UpdateVendors/VendoredDependency.cs

@@ -725,12 +725,27 @@ private static string FixSystemMemory(string filePath, string contents)
 
             contents = contents.Insert(namespaceIndex, usings);
 
+            // Leave these in the vendored namespace to avoid naming conflicts with various _other_ ThrowHelper files,
+            // and MemoryExtensions causes conflicts in the test projects - it's extension methods, so doesn't matter too much where it is
+            if (string.Equals(Path.GetFileName(filePath), "ThrowHelper.cs")
+             || string.Equals(Path.GetFileName(filePath), "MemoryExtensions.cs")
+             || string.Equals(Path.GetFileName(filePath), "MemoryExtensions.Portable.cs"))
+            {
+                contents = contents.Replace(
+                    "namespace System",
+                    "namespace Datadog.Trace.VendoredMicrosoftCode.System");
+            }
+
+            // Note that we leave everything in the System namespace where it is,
+            // so that the compiler can light up for things like Span<T>. It does raise the question
+            // of whether we should bother renaming _any_ of these APIs, but leaving as-is for now
+            // to avoid confusion
             contents = contents.Replace(
                                     "Datadog.Trace.VendoredMicrosoftCode.System..omponentModel.",
                                     "System.ComponentModel.")
                                .Replace(
                                     "Datadog.Trace.VendoredMicrosoftCode.System..UInt",
-                                    "Datadog.Trace.VendoredMicrosoftCode.System.NUInt")
+                                    "System.NUInt")
                                .Replace(
                                     "using Datadog.Trace.VendoredMicrosoftCode.System.ComponentModel",
                                     "using System.ComponentModel")
@@ -747,12 +762,8 @@ private static string FixSystemMemory(string filePath, string contents)
                                     "using Datadog.Trace.VendoredMicrosoftCode.System.Text",
                                     "using System.Text")
                                .Replace(
-                                    "namespace System\r\n",
-                                    "namespace System\n")
-                                // TODO: We should consider _not_ making this change in the future
-                               .Replace(
-                                    "namespace System\n",
-                                    "namespace Datadog.Trace.VendoredMicrosoftCode.System\n");
+                                    "ThrowHelper.",
+                                    "global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.");
 
             var resourceReplacements = new List<KeyValuePair<string, string>>
             {

tracer/src/Datadog.Trace/ExtensionMethods/StringBuilderExtensions.cs

@@ -5,6 +5,7 @@
 
 #nullable enable
 
+using System;
 using System.Text;
 
 #if !NETCOREAPP3_1_OR_GREATER

tracer/src/Datadog.Trace/Propagators/W3CTraceContextPropagator.cs

@@ -269,7 +269,6 @@ internal static bool TryParseTraceParent(string header, out W3CTraceParent trace
             string rawTraceId;
             string rawSpanId;
 
-#if NETCOREAPP
             var w3cTraceId = header.AsSpan(start: 3, length: 32);
             var w3cSpanId = header.AsSpan(start: 36, length: 16);
 
@@ -295,31 +294,6 @@ internal static bool TryParseTraceParent(string header, out W3CTraceParent trace
             {
                 return false;
             }
-#else
-            rawTraceId = header.Substring(startIndex: 3, length: 32);
-            rawSpanId = header.Substring(startIndex: 36, length: 16);
-
-            if (!HexString.TryParseTraceId(rawTraceId, out traceId) || traceId == TraceId.Zero)
-            {
-                return false;
-            }
-
-            if (!HexString.TryParseUInt64(rawSpanId, out parentId) || parentId == 0)
-            {
-                return false;
-            }
-
-            bool sampled;
-
-            if (HexString.TryParseByte(header.Substring(53, 2), out var traceFlags))
-            {
-                sampled = ((TraceFlags)traceFlags).HasFlagFast(TraceFlags.Sampled);
-            }
-            else
-            {
-                return false;
-            }
-#endif
 
             traceParent = new W3CTraceParent(
                 traceId: traceId,

tracer/src/Datadog.Trace/Vendors/System.Memory/System/Buffers/ArrayMemoryPool.ArrayMemoryPoolBuffer.cs

@@ -39,7 +39,7 @@ public Memory<T> Memory
                     T[] array = _array;
                     if (array == null)
                     {
-                        ThrowHelper.ThrowObjectDisposedException_ArrayMemoryPoolBuffer();
+                        global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowObjectDisposedException_ArrayMemoryPoolBuffer();
                     }
 
                     return new Memory<T>(array);

tracer/src/Datadog.Trace/Vendors/System.Memory/System/Buffers/ArrayMemoryPool.cs

@@ -31,7 +31,7 @@ public sealed override IMemoryOwner<T> Rent(int minimumBufferSize = -1)
             if (minimumBufferSize == -1)
                 minimumBufferSize = 1 + (4095 / Unsafe.SizeOf<T>());
             else if (((uint)minimumBufferSize) > s_maxBufferSize)
-                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.minimumBufferSize);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.minimumBufferSize);
 
             return new ArrayMemoryPoolBuffer(minimumBufferSize);
         }

tracer/src/Datadog.Trace/Vendors/System.Memory/System/Buffers/BuffersExtensions.cs

@@ -79,7 +79,7 @@ internal static class BuffersExtensions
         public static void CopyTo<T>(in this ReadOnlySequence<T> source, Span<T> destination)
         {
             if (source.Length > destination.Length)
-                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.destination);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.destination);
 
             if (source.IsSingleSegment)
             {

tracer/src/Datadog.Trace/Vendors/System.Memory/System/Buffers/ReadOnlySequence.cs

@@ -97,7 +97,7 @@ public ReadOnlySequence(ReadOnlySequenceSegment<T> startSegment, int startIndex,
                 (uint)startSegment.Memory.Length < (uint)startIndex ||
                 (uint)endSegment.Memory.Length < (uint)endIndex ||
                 (startSegment == endSegment && endIndex < startIndex))
-                ThrowHelper.ThrowArgumentValidationException(startSegment, startIndex, endSegment);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentValidationException(startSegment, startIndex, endSegment);
 
             _sequenceStart = new SequencePosition(startSegment, ReadOnlySequence.SegmentToSequenceStart(startIndex));
             _sequenceEnd = new SequencePosition(endSegment, ReadOnlySequence.SegmentToSequenceEnd(endIndex));
@@ -109,7 +109,7 @@ public ReadOnlySequence(ReadOnlySequenceSegment<T> startSegment, int startIndex,
         public ReadOnlySequence(T[] array)
         {
             if (array == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
 
             _sequenceStart = new SequencePosition(array, ReadOnlySequence.ArrayToSequenceStart(0));
             _sequenceEnd = new SequencePosition(array, ReadOnlySequence.ArrayToSequenceEnd(array.Length));
@@ -123,7 +123,7 @@ public ReadOnlySequence(T[] array, int start, int length)
             if (array == null ||
                 (uint)start > (uint)array.Length ||
                 (uint)length > (uint)(array.Length - start))
-                ThrowHelper.ThrowArgumentValidationException(array, start);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentValidationException(array, start);
 
             _sequenceStart = new SequencePosition(array, ReadOnlySequence.ArrayToSequenceStart(start));
             _sequenceEnd = new SequencePosition(array, ReadOnlySequence.ArrayToSequenceEnd(start + length));
@@ -150,15 +150,15 @@ public ReadOnlySequence(ReadOnlyMemory<T> memory)
             else if (typeof(T) == typeof(char))
             {
                 if (!MemoryMarshal.TryGetString(((ReadOnlyMemory<char>)(object)memory), out string text, out int start, out length))
-                    ThrowHelper.ThrowInvalidOperationException();
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowInvalidOperationException();
 
                 _sequenceStart = new SequencePosition(text, ReadOnlySequence.StringToSequenceStart(start));
                 _sequenceEnd = new SequencePosition(text, ReadOnlySequence.StringToSequenceEnd(start + length));
             }
             else
             {
                 // Should never be reached
-                ThrowHelper.ThrowInvalidOperationException();
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowInvalidOperationException();
                 _sequenceStart = default;
                 _sequenceEnd = default;
             }
@@ -172,7 +172,7 @@ public ReadOnlySequence(ReadOnlyMemory<T> memory)
         public ReadOnlySequence<T> Slice(long start, long length)
         {
             if (start < 0 || length < 0)
-                ThrowHelper.ThrowStartOrEndArgumentValidationException(start);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(start);
 
             SequencePosition begin;
             SequencePosition end;
@@ -201,7 +201,7 @@ public ReadOnlySequence<T> Slice(long start, long length)
                 else
                 {
                     if (currentLength < 0)
-                        ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                        global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
 
                     begin = SeekMultiSegment(startSegment.Next, endObject, endIndex, start - currentLength, ExceptionArgument.start);
 
@@ -216,7 +216,7 @@ public ReadOnlySequence<T> Slice(long start, long length)
                     else
                     {
                         if (endIndex - beginIndex < length)
-                            ThrowHelper.ThrowStartOrEndArgumentValidationException(0);  // Passing value >= 0 means throw exception on length argument
+                            global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(0);  // Passing value >= 0 means throw exception on length argument
 
                         end = new SequencePosition(beginObject, beginIndex + (int)length);
                     }
@@ -225,13 +225,13 @@ public ReadOnlySequence<T> Slice(long start, long length)
             else
             {
                 if (endIndex - startIndex < start)
-                    ThrowHelper.ThrowStartOrEndArgumentValidationException(-1); // Passing value < 0 means throw exception on start argument
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(-1); // Passing value < 0 means throw exception on start argument
 
                 startIndex += (int)start;
                 begin = new SequencePosition(startObject, startIndex);
 
                 if (endIndex - startIndex < length)
-                    ThrowHelper.ThrowStartOrEndArgumentValidationException(0);  // Passing value >= 0 means throw exception on length argument
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(0);  // Passing value >= 0 means throw exception on length argument
 
                 end = new SequencePosition(startObject, startIndex + (int)length);
             }
@@ -247,7 +247,7 @@ public ReadOnlySequence<T> Slice(long start, long length)
         public ReadOnlySequence<T> Slice(long start, SequencePosition end)
         {
             if (start < 0)
-                ThrowHelper.ThrowStartOrEndArgumentValidationException(start);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(start);
 
             uint sliceEndIndex = (uint)GetIndex(end);
             object sliceEndObject = end.GetObject();
@@ -263,11 +263,11 @@ public ReadOnlySequence<T> Slice(long start, SequencePosition end)
             {
                 if (!InRange(sliceEndIndex, startIndex, endIndex))
                 {
-                    ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
                 }
 
                 if (sliceEndIndex - startIndex < start)
-                    ThrowHelper.ThrowStartOrEndArgumentValidationException(-1); // Passing value < 0 means throw exception on start argument
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(-1); // Passing value < 0 means throw exception on start argument
 
                 goto FoundInFirstSegment;
             }
@@ -284,12 +284,12 @@ public ReadOnlySequence<T> Slice(long start, SequencePosition end)
                 startRange,
                 (ulong)(((ReadOnlySequenceSegment<T>)endObject).RunningIndex + endIndex)))
             {
-                ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
             }
 
             if (startRange + (ulong)start > sliceRange)
             {
-                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
             }
 
             int currentLength = startSegment.Memory.Length - (int)startIndex;
@@ -298,7 +298,7 @@ public ReadOnlySequence<T> Slice(long start, SequencePosition end)
             if (currentLength <= start)
             {
                 if (currentLength < 0)
-                    ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
 
                 // End of segment. Move to start of next.
                 SequencePosition begin = SeekMultiSegment(startSegment.Next, sliceEndObject, (int)sliceEndIndex, start - currentLength, ExceptionArgument.start);
@@ -333,15 +333,15 @@ public ReadOnlySequence<T> Slice(SequencePosition start, long length)
             {
                 if (!InRange(sliceStartIndex, startIndex, endIndex))
                 {
-                    ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
                 }
 
                 if (length < 0)
                     // Passing value >= 0 means throw exception on length argument
-                    ThrowHelper.ThrowStartOrEndArgumentValidationException(0);
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(0);
 
                 if (endIndex - sliceStartIndex < length)
-                    ThrowHelper.ThrowStartOrEndArgumentValidationException(0);
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(0);
 
                 goto FoundInFirstSegment;
             }
@@ -356,16 +356,16 @@ public ReadOnlySequence<T> Slice(SequencePosition start, long length)
             Debug.Assert(sliceStartIndex >= 0 && startIndex >= 0 && endIndex >= 0);
             if (!InRange(sliceRange, startRange, endRange))
             {
-                ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
             }
 
             if (length < 0)
                 // Passing value >= 0 means throw exception on length argument
-                ThrowHelper.ThrowStartOrEndArgumentValidationException(0);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(0);
 
             if (sliceRange + (ulong)length > endRange)
             {
-                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.length);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.length);
             }
 
             int currentLength = sliceStartSegment.Memory.Length - (int)sliceStartIndex;
@@ -374,7 +374,7 @@ public ReadOnlySequence<T> Slice(SequencePosition start, long length)
             if (currentLength < length)
             {
                 if (currentLength < 0)
-                    ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
+                    global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_PositionOutOfRange();
 
                 // End of segment. Move to start of next.
                 SequencePosition end = SeekMultiSegment(sliceStartSegment.Next, endObject, (int)endIndex, length - currentLength, ExceptionArgument.length);
@@ -438,7 +438,7 @@ public ReadOnlySequence<T> Slice(SequencePosition start)
         public ReadOnlySequence<T> Slice(long start)
         {
             if (start < 0)
-                ThrowHelper.ThrowStartOrEndArgumentValidationException(start);
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowStartOrEndArgumentValidationException(start);
 
             if (start == 0)
                 return this;
@@ -485,7 +485,7 @@ public override string ToString()
         public SequencePosition GetPosition(long offset, SequencePosition origin)
         {
             if (offset < 0)
-                ThrowHelper.ThrowArgumentOutOfRangeException_OffsetOutOfRange();
+                global::Datadog.Trace.VendoredMicrosoftCode.System.ThrowHelper.ThrowArgumentOutOfRangeException_OffsetOutOfRange();
 
             return Seek(origin, _sequenceEnd, offset, ExceptionArgument.offset);
         }