Add Utf8.TryWrite

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -517,6 +517,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\IObserver.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IProgress.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\ISpanFormattable.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IUtf8SpanFormattable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Lazy.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\LazyOfTTMetadata.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\LoaderOptimization.cs" />

src/libraries/System.Private.CoreLib/src/System/IUtf8SpanFormattable.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System
+{
+    /// <summary>Provides functionality to format the string representation of an object into a span as UTF8.</summary>
+    public interface IUtf8SpanFormattable
+    {
+        /// <summary>Tries to format the value of the current instance as UTF8 into the provided span of bytes.</summary>
+        /// <param name="destination">When this method returns, this instance's value formatted as a span of bytes.</param>
+        /// <param name="bytesWritten">When this method returns, the number of bytes that were written in <paramref name="destination"/>.</param>
+        /// <param name="format">A span containing the characters that represent a standard or custom format string that defines the acceptable format for <paramref name="destination"/>.</param>
+        /// <param name="provider">An optional object that supplies culture-specific formatting information for <paramref name="destination"/>.</param>
+        /// <returns><see langword="true"/> if the formatting was successful; otherwise, <see langword="false"/>.</returns>
+        /// <remarks>
+        /// An implementation of this interface should produce the same string of characters as an implementation of <see cref="IFormattable.ToString"/> or <see cref="ISpanFormattable.TryFormat"/>
+        /// on the same type. TryFormat should return false only if there is not enough space in the destination buffer; any other failures should throw an exception.
+        /// </remarks>
+        bool TryFormat(Span<byte> destination, out int bytesWritten, ReadOnlySpan<char> format, IFormatProvider? provider);
+    }
+}

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -3865,6 +3865,10 @@ public partial interface ISpanParsable<TSelf> : System.IParsable<TSelf> where TS
         static abstract TSelf Parse(System.ReadOnlySpan<char> s, System.IFormatProvider? provider);
         static abstract bool TryParse(System.ReadOnlySpan<char> s, System.IFormatProvider? provider, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TSelf result);
     }
+    public partial interface IUtf8SpanFormattable
+    {
+        bool TryFormat(System.Span<byte> destination, out int bytesWritten, System.ReadOnlySpan<char> format, System.IFormatProvider? provider);
+    }
     public partial class Lazy<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>
     {
         public Lazy() { }
@@ -14437,6 +14441,29 @@ public static partial class Utf8
     {
         public static System.Buffers.OperationStatus FromUtf16(System.ReadOnlySpan<char> source, System.Span<byte> destination, out int charsRead, out int bytesWritten, bool replaceInvalidSequences = true, bool isFinalBlock = true) { throw null; }
         public static System.Buffers.OperationStatus ToUtf16(System.ReadOnlySpan<byte> source, System.Span<char> destination, out int bytesRead, out int charsWritten, bool replaceInvalidSequences = true, bool isFinalBlock = true) { throw null; }
+        public static bool TryWrite(System.Span<byte> destination, [System.Runtime.CompilerServices.InterpolatedStringHandlerArgumentAttribute("destination")] ref System.Text.Unicode.Utf8.TryWriteInterpolatedStringHandler handler, out int bytesWritten) { throw null; }
+        public static bool TryWrite(System.Span<byte> destination, IFormatProvider? provider, [System.Runtime.CompilerServices.InterpolatedStringHandlerArgumentAttribute("destination", "provider")] ref System.Text.Unicode.Utf8.TryWriteInterpolatedStringHandler handler, out int bytesWritten) { throw null; }
+        [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
+        [System.Runtime.CompilerServices.InterpolatedStringHandlerAttribute]
+        public ref struct TryWriteInterpolatedStringHandler
+        {
+            private readonly object _dummy;
+            private readonly int _dummyPrimitive;
+            public TryWriteInterpolatedStringHandler(int literalLength, int formattedCount, System.Span<byte> destination, out bool shouldAppend) { throw null; }
+            public TryWriteInterpolatedStringHandler(int literalLength, int formattedCount, System.Span<byte> destination, IFormatProvider? provider, out bool shouldAppend) { throw null; }
+            public bool AppendLiteral(string value) { throw null; }
+            public bool AppendFormatted(scoped System.ReadOnlySpan<char> value) { throw null; }
+            public bool AppendFormatted(scoped System.ReadOnlySpan<char> value, int alignment = 0, string? format = null) { throw null; }
+            public bool AppendFormatted(scoped System.ReadOnlySpan<byte> utf8Value) { throw null; }
+            public bool AppendFormatted(scoped System.ReadOnlySpan<byte> utf8Value, int alignment = 0, string? format = null) { throw null; }
+            public bool AppendFormatted<T>(T value) { throw null; }
+            public bool AppendFormatted<T>(T value, string? format) { throw null; }
+            public bool AppendFormatted<T>(T value, int alignment) { throw null; }
+            public bool AppendFormatted<T>(T value, int alignment, string? format) { throw null; }
+            public bool AppendFormatted(object? value, int alignment = 0, string? format = null) { throw null; }
+            public bool AppendFormatted(string? value) { throw null; }
+            public bool AppendFormatted(string? value, int alignment = 0, string? format = null) { throw null; }
+        }
     }
 }
 namespace System.Threading

src/libraries/System.Runtime/tests/System.Runtime.Tests.csproj

@@ -317,6 +317,7 @@
     <Compile Include="System\Text\RuneTests.TestData.cs" />
     <Compile Include="System\Text\Unicode\Utf16UtilityTests.ValidateChars.cs" />
     <Compile Include="System\Text\Unicode\Utf8Tests.cs" />
+    <Compile Include="System\Text\Unicode\Utf8Tests.TryWrite.cs" />
     <Compile Include="System\Text\Unicode\Utf8UtilityTests.ValidateBytes.cs" />
     <Compile Include="System\ArgIteratorTests.cs" />
     <Compile Include="$(CommonPath)..\tests\System\RealFormatterTestsBase.cs" Link="System\RealFormatterTestsBase.cs" />