Use scoped more in dotnet/runtime (#71589)

* Use scoped more in dotnet/runtime

This PR addresses a few issues:
- Exposes the new {ReadOnly}Span constructors that accept a ref.
- Uses those new constructors outside of corelib (they were previously internal and used only inside of corelib).
- Makes several members of Utf8JsonReader readonly in order to enable stackalloc'd spans to be used in ValueTextEquals calls.
- Makes several span arguments to SequenceReader scoped in order to enable stackalloc'd spans to be used with those calls.
- Removes all stackalloc T[0], replacing it with scoped locals.
- Removes some use of stackalloc'ing into a pointer and then manually wrapping into a span, instead directly stackalloc'ing into a span.  This is possible now in more cases due to the new language validation rules.
- Replaced some use of MemoryMarshal.GetReference(MemoryMarshal.CreateSpan(...)) with Unsafe.AsRef.

* Address PR feedback

src/coreclr/System.Private.CoreLib/src/System/Reflection/Associates.cs

@@ -50,7 +50,7 @@ internal static bool IncludeAccessor(MethodInfo? associate, bool nonPublic)
 
             bool isInherited = declaredType != reflectedType;
 
-            Span<IntPtr> genericArgumentHandles = stackalloc IntPtr[0];
+            scoped Span<IntPtr> genericArgumentHandles = default;
             RuntimeType[] genericArguments = declaredType.TypeHandle.GetInstantiationInternal();
             if (genericArguments != null)
             {

src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs

@@ -1411,8 +1411,8 @@ public RuntimeTypeHandle ResolveTypeHandle(int typeToken, RuntimeTypeHandle[]? t
             RuntimeModule module = GetRuntimeModule();
             ValidateModulePointer(module);
 
-            ReadOnlySpan<IntPtr> typeInstantiationContextHandles = stackalloc IntPtr[0];
-            ReadOnlySpan<IntPtr> methodInstantiationContextHandles = stackalloc IntPtr[0];
+            scoped ReadOnlySpan<IntPtr> typeInstantiationContextHandles = default;
+            scoped ReadOnlySpan<IntPtr> methodInstantiationContextHandles = default;
 
             // defensive copy of user-provided array, per CopyRuntimeTypeHandles contract
             if (typeInstantiationContext?.Length > 0)
@@ -1517,8 +1517,8 @@ public RuntimeFieldHandle ResolveFieldHandle(int fieldToken, RuntimeTypeHandle[]
             RuntimeModule module = GetRuntimeModule();
             ValidateModulePointer(module);
 
-            ReadOnlySpan<IntPtr> typeInstantiationContextHandles = stackalloc IntPtr[0];
-            ReadOnlySpan<IntPtr> methodInstantiationContextHandles = stackalloc IntPtr[0];
+            scoped ReadOnlySpan<IntPtr> typeInstantiationContextHandles = default;
+            scoped ReadOnlySpan<IntPtr> methodInstantiationContextHandles = default;
 
             // defensive copy of user-provided array, per CopyRuntimeTypeHandles contract
             if (typeInstantiationContext?.Length > 0)

src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs

@@ -1284,7 +1284,7 @@ private RuntimePropertyInfo[] PopulateProperties(Filter filter)
 
                         // All elements initialized to false.
                         int numVirtuals = RuntimeTypeHandle.GetNumVirtuals(declaringType);
-                        Span<bool> usedSlots = stackalloc bool[0];
+                        scoped Span<bool> usedSlots;
                         if (numVirtuals <= 128) // arbitrary stack limit
                         {
                             usedSlots = stackalloc bool[numVirtuals];

src/libraries/Common/src/Interop/Windows/SspiCli/SSPIWrapper.cs

@@ -201,20 +201,12 @@ public static int QuerySecurityContextToken(ISSPIInterface secModule, SafeDelete
 
         public static bool QueryBlittableContextAttributes<T>(ISSPIInterface secModule, SafeDeleteContext securityContext, Interop.SspiCli.ContextAttribute contextAttribute, ref T attribute) where T : unmanaged
         {
-            Span<T> span =
-#if NETSTANDARD2_0
-                stackalloc T[1] { attribute };
-#else
-                MemoryMarshal.CreateSpan(ref attribute, 1);
-#endif
+            Span<T> span = new Span<T>(ref attribute);
             int errorCode = secModule.QueryContextAttributes(
                 securityContext, contextAttribute,
                 MemoryMarshal.AsBytes(span),
                 null,
                 out SafeHandle? sspiHandle);
-#if NETSTANDARD2_0
-            attribute = span[0];
-#endif
 
             using (sspiHandle)
             {
@@ -230,20 +222,12 @@ public static bool QueryBlittableContextAttributes<T>(ISSPIInterface secModule,
 
         public static bool QueryBlittableContextAttributes<T>(ISSPIInterface secModule, SafeDeleteContext securityContext, Interop.SspiCli.ContextAttribute contextAttribute, Type safeHandleType, out SafeHandle? sspiHandle, ref T attribute) where T : unmanaged
         {
-            Span<T> span =
-#if NETSTANDARD2_0
-                stackalloc T[1] { attribute };
-#else
-                MemoryMarshal.CreateSpan(ref attribute, 1);
-#endif
+            Span<T> span = new Span<T>(ref attribute);
             int errorCode = secModule.QueryContextAttributes(
                 securityContext, contextAttribute,
                 MemoryMarshal.AsBytes(span),
                 safeHandleType,
                 out sspiHandle);
-#if NETSTANDARD2_0
-            attribute = span[0];
-#endif
 
             if (errorCode != 0)
             {
@@ -318,21 +302,13 @@ public static bool QueryContextAttributes_SECPKG_ATTR_REMOTE_CERT_CHAIN(ISSPIInt
 
         public static bool QueryContextAttributes_SECPKG_ATTR_ISSUER_LIST_EX(ISSPIInterface secModule, SafeDeleteContext securityContext, ref Interop.SspiCli.SecPkgContext_IssuerListInfoEx ctx, out SafeHandle? sspiHandle)
         {
-            Span<Interop.SspiCli.SecPkgContext_IssuerListInfoEx> buffer =
-#if NETSTANDARD2_0
-                stackalloc Interop.SspiCli.SecPkgContext_IssuerListInfoEx[1] { ctx };
-#else
-                MemoryMarshal.CreateSpan(ref ctx, 1);
-#endif
+            Span<Interop.SspiCli.SecPkgContext_IssuerListInfoEx> buffer = new Span<Interop.SspiCli.SecPkgContext_IssuerListInfoEx>(ref ctx);
             int errorCode = secModule.QueryContextAttributes(
                 securityContext,
                 Interop.SspiCli.ContextAttribute.SECPKG_ATTR_ISSUER_LIST_EX,
                 MemoryMarshal.AsBytes(buffer),
                 typeof(SafeFreeContextBuffer),
                 out sspiHandle);
-#if NETSTANDARD2_0
-            ctx = buffer[0];
-#endif
 
             if (errorCode != 0)
             {

src/libraries/Common/src/System/HexConverter.cs

@@ -196,16 +196,9 @@ public static void EncodeToUtf16(ReadOnlySpan<byte> bytes, Span<char> chars, Cas
         public static unsafe string ToString(ReadOnlySpan<byte> bytes, Casing casing = Casing.Upper)
         {
 #if NETFRAMEWORK || NETSTANDARD2_0
-            Span<char> result = stackalloc char[0];
-            if (bytes.Length > 16)
-            {
-                var array = new char[bytes.Length * 2];
-                result = array.AsSpan();
-            }
-            else
-            {
-                result = stackalloc char[bytes.Length * 2];
-            }
+            Span<char> result = bytes.Length > 16 ?
+                new char[bytes.Length * 2].AsSpan() :
+                stackalloc char[bytes.Length * 2];
 
             int pos = 0;
             foreach (byte b in bytes)

src/libraries/Common/src/System/Net/NTAuthentication.Managed.cs

@@ -428,7 +428,7 @@ private static unsafe void SetField(ref MessageField field, int length, int offs
                 throw new Win32Exception(NTE_FAIL);
             }
 
-            Span<byte> span = MemoryMarshal.AsBytes(MemoryMarshal.CreateSpan(ref field, 1));
+            Span<byte> span = MemoryMarshal.AsBytes(new Span<MessageField>(ref field));
             BinaryPrimitives.WriteInt16LittleEndian(span, (short)length);
             BinaryPrimitives.WriteInt16LittleEndian(span.Slice(2), (short)length);
             BinaryPrimitives.WriteInt32LittleEndian(span.Slice(4), offset);

src/libraries/Common/src/System/Security/Cryptography/ECDiffieHellmanAndroid.Derive.cs

@@ -138,7 +138,7 @@ public override byte[] DeriveKeyTls(ECDiffieHellmanPublicKey otherPartyPublicKey
                     }
 
                     // Indicate that secret can hold stackallocs from nested scopes
-                    Span<byte> secret = stackalloc byte[0];
+                    scoped Span<byte> secret;
 
                     // Arbitrary limit. But it covers secp521r1, which is the biggest common case.
                     const int StackAllocMax = 66;

src/libraries/Common/src/System/Security/Cryptography/ECDiffieHellmanOpenSsl.Derive.cs

@@ -143,7 +143,7 @@ public override byte[] DeriveKeyTls(ECDiffieHellmanPublicKey otherPartyPublicKey
                     secretLength = (int)secretLengthU;
 
                     // Indicate that secret can hold stackallocs from nested scopes
-                    Span<byte> secret = stackalloc byte[0];
+                    scoped Span<byte> secret;
 
                     // Arbitrary limit. But it covers secp521r1, which is the biggest common case.
                     const int StackAllocMax = 66;

src/libraries/Common/src/System/Security/Cryptography/PasswordBasedEncryption.cs

@@ -169,7 +169,7 @@ internal static unsafe int Decrypt(
                 using (IncrementalHash hasher = IncrementalHash.CreateHash(digestAlgorithmName))
                 {
                     Span<byte> buf = stackalloc byte[128];
-                    ReadOnlySpan<byte> effectivePasswordBytes = stackalloc byte[0];
+                    scoped ReadOnlySpan<byte> effectivePasswordBytes = default;
                     byte[]? rented = null;
                     System.Text.Encoding? encoding = null;
 
@@ -464,7 +464,7 @@ private static unsafe int Pbes2Decrypt(
             Span<byte> destination)
         {
             Span<byte> buf = stackalloc byte[128];
-            ReadOnlySpan<byte> effectivePasswordBytes = stackalloc byte[0];
+            scoped ReadOnlySpan<byte> effectivePasswordBytes = default;
             byte[]? rented = null;
             System.Text.Encoding? encoding = null;
 

src/libraries/Common/src/System/Security/Cryptography/Pkcs12Kdf.cs

@@ -134,7 +134,7 @@ private static void Derive(
 
             // 4.  Set I=S||P to be the concatenation of S and P.
             int ILen = checked(SLen + PLen);
-            Span<byte> I = stackalloc byte[0];
+            scoped Span<byte> I;
             byte[]? IRented = null;
 
             if (ILen <= 1024)

src/libraries/Common/src/System/Security/Cryptography/RSAAndroid.cs

@@ -121,7 +121,7 @@ public override bool TryDecrypt(
                 // To prevent the OOB write, decrypt into a temporary buffer.
                 if (destination.Length < keySizeBytes)
                 {
-                    Span<byte> tmp = stackalloc byte[0];
+                    scoped Span<byte> tmp;
                     byte[]? rent = null;
 
                     // RSA up through 4096 stackalloc

src/libraries/System.Console/src/System/ConsolePal.Unix.cs

@@ -615,7 +615,7 @@ static unsafe bool AppendToStdInReaderUntil(byte toFind, StdInReader reader, Spa
                         }
 
                         // Otherwise, push it back into the reader's extra buffer.
-                        reader.AppendExtraBuffer(MemoryMarshal.CreateReadOnlySpan(ref b, 1));
+                        reader.AppendExtraBuffer(new ReadOnlySpan<byte>(in b));
                     }
                 }
 
@@ -636,7 +636,7 @@ static void ReadRowOrCol(int startExclusive, int endExclusive, StdInReader reade
                         }
                         else
                         {
-                            reader.AppendExtraBuffer(MemoryMarshal.CreateReadOnlySpan(ref b, 1));
+                            reader.AppendExtraBuffer(new ReadOnlySpan<byte>(in b));
                         }
                     }
 
@@ -1363,7 +1363,7 @@ internal static void WriteStdoutAnsiString(string? value, bool mayChangeCursorPo
             if (string.IsNullOrEmpty(value))
                 return;
 
-            Span<byte> data = stackalloc byte[0];
+            scoped Span<byte> data;
             if (value.Length <= 256) // except for extremely rare cases, ANSI escape strings are very short
             {
                 data = stackalloc byte[Encoding.UTF8.GetMaxByteCount(value.Length)];

src/libraries/System.Console/src/System/IO/ConsoleStream.cs

@@ -26,7 +26,7 @@ public override void Write(byte[] buffer, int offset, int count)
             Write(new ReadOnlySpan<byte>(buffer, offset, count));
         }
 
-        public override void WriteByte(byte value) => Write(MemoryMarshal.CreateReadOnlySpan(ref value, 1));
+        public override void WriteByte(byte value) => Write(new ReadOnlySpan<byte>(in value));
 
         public override int Read(byte[] buffer, int offset, int count)
         {
@@ -37,7 +37,7 @@ public override int Read(byte[] buffer, int offset, int count)
         public override int ReadByte()
         {
             byte b = 0;
-            int result = Read(MemoryMarshal.CreateSpan(ref b, 1));
+            int result = Read(new Span<byte>(ref b));
             return result != 0 ? b : -1;
         }
 

src/libraries/System.Formats.Asn1/src/System/Formats/Asn1/AsnWriter.GeneralizedTime.cs

@@ -67,7 +67,7 @@ private void WriteGeneralizedTimeCore(
             // We're only loading in sub-second ticks.
             // Ticks are defined as 1e-7 seconds, so their printed form
             // is at the longest "0.1234567", or 9 bytes.
-            Span<byte> fraction = stackalloc byte[0];
+            scoped Span<byte> fraction = default;
 
             if (!omitFractionalSeconds)
             {

src/libraries/System.Formats.Tar/src/System/Formats/Tar/SubReadStream.cs

@@ -127,7 +127,7 @@ public override int Read(Span<byte> destination)
         public override int ReadByte()
         {
             byte b = default;
-            return Read(MemoryMarshal.CreateSpan(ref b, 1)) == 1 ? b : -1;
+            return Read(new Span<byte>(ref b)) == 1 ? b : -1;
         }
 
         public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/dec/BrotliStream.Decompress.cs

@@ -44,7 +44,7 @@ public override int Read(byte[] buffer, int offset, int count)
         public override int ReadByte()
         {
             byte b = default;
-            int bytesRead = Read(MemoryMarshal.CreateSpan(ref b, 1));
+            int bytesRead = Read(new Span<byte>(ref b));
             return bytesRead != 0 ? b : -1;
         }
 

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/enc/BrotliStream.Compress.cs

@@ -46,7 +46,7 @@ public override void Write(byte[] buffer, int offset, int count)
         /// <para>The encoder ran into invalid data.</para></exception>
         public override void WriteByte(byte value)
         {
-            WriteCore(MemoryMarshal.CreateReadOnlySpan(ref value, 1));
+            WriteCore(new ReadOnlySpan<byte>(in value));
         }
 
         /// <summary>Writes a sequence of bytes to the current Brotli stream from a read-only byte span and advances the current position within this Brotli stream by the number of bytes written.</summary>

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateManaged/DeflateManagedStream.cs

@@ -143,7 +143,7 @@ public override int Read(Span<byte> buffer)
         public override int ReadByte()
         {
             byte b = default;
-            return Read(MemoryMarshal.CreateSpan(ref b, 1)) == 1 ? b : -1;
+            return Read(new Span<byte>(ref b)) == 1 ? b : -1;
         }
 
         private void EnsureNotDisposed()

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

@@ -488,7 +488,7 @@ public override void WriteByte(byte value)
             }
             else
             {
-                WriteCore(MemoryMarshal.CreateReadOnlySpan(ref value, 1));
+                WriteCore(new ReadOnlySpan<byte>(in value));
             }
         }
 

src/libraries/System.IO.Compression/src/System/IO/Compression/GZipStream.cs

@@ -123,7 +123,7 @@ public override void WriteByte(byte value)
             else
             {
                 CheckDeflateStream();
-                _deflateStream.WriteCore(MemoryMarshal.CreateReadOnlySpan(ref value, 1));
+                _deflateStream.WriteCore(new ReadOnlySpan<byte>(in value));
             }
         }
 

src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.cs

@@ -1237,7 +1237,7 @@ public override void Write(ReadOnlySpan<byte> source)
             }
 
             public override void WriteByte(byte value) =>
-                Write(MemoryMarshal.CreateReadOnlySpan(ref value, 1));
+                Write(new ReadOnlySpan<byte>(in value));
 
             public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
             {

src/libraries/System.IO.Compression/src/System/IO/Compression/ZipCustomStreams.cs

@@ -329,7 +329,7 @@ public override int Read(Span<byte> destination)
         public override int ReadByte()
         {
             byte b = default;
-            return Read(MemoryMarshal.CreateSpan(ref b, 1)) == 1 ? b : -1;
+            return Read(new Span<byte>(ref b)) == 1 ? b : -1;
         }
 
         public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
@@ -542,7 +542,7 @@ public override void Write(ReadOnlySpan<byte> source)
         }
 
         public override void WriteByte(byte value) =>
-            Write(MemoryMarshal.CreateReadOnlySpan(ref value, 1));
+            Write(new ReadOnlySpan<byte>(in value));
 
         public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {

src/libraries/System.Memory/ref/System.Memory.cs

@@ -312,28 +312,28 @@ public static partial class SequenceReaderExtensions
         public readonly System.ReadOnlySpan<T> UnreadSpan { get { throw null; } }
         public void Advance(long count) { }
         public long AdvancePast(T value) { throw null; }
-        public long AdvancePastAny(System.ReadOnlySpan<T> values) { throw null; }
+        public long AdvancePastAny(scoped System.ReadOnlySpan<T> values) { throw null; }
         public long AdvancePastAny(T value0, T value1) { throw null; }
         public long AdvancePastAny(T value0, T value1, T value2) { throw null; }
         public long AdvancePastAny(T value0, T value1, T value2, T value3) { throw null; }
         public void AdvanceToEnd() { throw null; }
-        public bool IsNext(System.ReadOnlySpan<T> next, bool advancePast = false) { throw null; }
+        public bool IsNext(scoped System.ReadOnlySpan<T> next, bool advancePast = false) { throw null; }
         public bool IsNext(T next, bool advancePast = false) { throw null; }
         public void Rewind(long count) { }
         public bool TryAdvanceTo(T delimiter, bool advancePastDelimiter = true) { throw null; }
-        public bool TryAdvanceToAny(System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
+        public bool TryAdvanceToAny(scoped System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
         public readonly bool TryCopyTo(System.Span<T> destination) { throw null; }
         public readonly bool TryPeek(out T value) { throw null; }
         public readonly bool TryPeek(long offset, out T value) { throw null; }
         public bool TryRead(out T value) { throw null; }
-        public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
+        public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, scoped System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, T delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, T delimiter, T delimiterEscape, bool advancePastDelimiter = true) { throw null; }
-        public bool TryReadTo(out System.ReadOnlySpan<T> span, System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
+        public bool TryReadTo(out System.ReadOnlySpan<T> span, scoped System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.ReadOnlySpan<T> span, T delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.ReadOnlySpan<T> span, T delimiter, T delimiterEscape, bool advancePastDelimiter = true) { throw null; }
-        public bool TryReadToAny(out System.Buffers.ReadOnlySequence<T> sequence, System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
-        public bool TryReadToAny(out System.ReadOnlySpan<T> span, System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
+        public bool TryReadToAny(out System.Buffers.ReadOnlySequence<T> sequence, scoped System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
+        public bool TryReadToAny(out System.ReadOnlySpan<T> span, scoped System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadExact(int count, out System.Buffers.ReadOnlySequence<T> sequence) { throw null; }
     }
     public readonly partial struct StandardFormat : System.IEquatable<System.Buffers.StandardFormat>