From ac84ea6e241ad2d2cde346144b2c4b3a5d64fa1d Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Thu, 17 Mar 2022 07:30:59 -0400
Subject: [PATCH] Replace StringBuilder with ValueStringBuilder in
 AssemblyName.FullName (#66750)

---
 ...alueStringBuilder.AppendSpanFormattable.cs |  2 +-
 .../Reflection/AssemblyNameFormatter.cs       | 54 ++++++++++---------
 2 files changed, 29 insertions(+), 27 deletions(-)

diff --git a/src/libraries/Common/src/System/Text/ValueStringBuilder.AppendSpanFormattable.cs b/src/libraries/Common/src/System/Text/ValueStringBuilder.AppendSpanFormattable.cs
index 6ccde43ef6a50..04e9fcbdb5524 100644
--- a/src/libraries/Common/src/System/Text/ValueStringBuilder.AppendSpanFormattable.cs
+++ b/src/libraries/Common/src/System/Text/ValueStringBuilder.AppendSpanFormattable.cs
@@ -5,7 +5,7 @@ namespace System.Text
 {
     internal ref partial struct ValueStringBuilder
     {
-        internal void AppendSpanFormattable<T>(T value, string? format, IFormatProvider? provider) where T : ISpanFormattable
+        internal void AppendSpanFormattable<T>(T value, string? format = null, IFormatProvider? provider = null) where T : ISpanFormattable
         {
             if (value.TryFormat(_chars.Slice(_pos), out int charsWritten, format, provider))
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/AssemblyNameFormatter.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/AssemblyNameFormatter.cs
index bdadec8d2c8af..bb13826d2c321 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/AssemblyNameFormatter.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/AssemblyNameFormatter.cs
@@ -15,31 +15,31 @@ public static string ComputeDisplayName(string name, Version? version, string? c
             const int PUBLIC_KEY_TOKEN_LEN = 8;
             Debug.Assert(name.Length != 0);
 
-            StringBuilder sb = new StringBuilder();
-            sb.AppendQuoted(name);
+            var vsb = new ValueStringBuilder(stackalloc char[256]);
+            vsb.AppendQuoted(name);
 
             if (version != null)
             {
                 Version canonicalizedVersion = version.CanonicalizeVersion();
                 if (canonicalizedVersion.Major != ushort.MaxValue)
                 {
-                    sb.Append(", Version=");
-                    sb.Append(canonicalizedVersion.Major);
+                    vsb.Append(", Version=");
+                    vsb.AppendSpanFormattable(canonicalizedVersion.Major);
 
                     if (canonicalizedVersion.Minor != ushort.MaxValue)
                     {
-                        sb.Append('.');
-                        sb.Append(canonicalizedVersion.Minor);
+                        vsb.Append('.');
+                        vsb.AppendSpanFormattable(canonicalizedVersion.Minor);
 
                         if (canonicalizedVersion.Build != ushort.MaxValue)
                         {
-                            sb.Append('.');
-                            sb.Append(canonicalizedVersion.Build);
+                            vsb.Append('.');
+                            vsb.AppendSpanFormattable(canonicalizedVersion.Build);
 
                             if (canonicalizedVersion.Revision != ushort.MaxValue)
                             {
-                                sb.Append('.');
-                                sb.Append(canonicalizedVersion.Revision);
+                                vsb.Append('.');
+                                vsb.AppendSpanFormattable(canonicalizedVersion.Revision);
                             }
                         }
                     }
@@ -50,8 +50,8 @@ public static string ComputeDisplayName(string name, Version? version, string? c
             {
                 if (cultureName.Length == 0)
                     cultureName = "neutral";
-                sb.Append(", Culture=");
-                sb.AppendQuoted(cultureName);
+                vsb.Append(", Culture=");
+                vsb.AppendQuoted(cultureName);
             }
 
             if (pkt != null)
@@ -59,27 +59,29 @@ public static string ComputeDisplayName(string name, Version? version, string? c
                 if (pkt.Length > PUBLIC_KEY_TOKEN_LEN)
                     throw new ArgumentException();
 
-                sb.Append(", PublicKeyToken=");
+                vsb.Append(", PublicKeyToken=");
                 if (pkt.Length == 0)
-                    sb.Append("null");
+                {
+                    vsb.Append("null");
+                }
                 else
                 {
-                    sb.Append(HexConverter.ToString(pkt, HexConverter.Casing.Lower));
+                    HexConverter.EncodeToUtf16(pkt, vsb.AppendSpan(pkt.Length * 2), HexConverter.Casing.Lower);
                 }
             }
 
             if (0 != (flags & AssemblyNameFlags.Retargetable))
-                sb.Append(", Retargetable=Yes");
+                vsb.Append(", Retargetable=Yes");
 
             if (contentType == AssemblyContentType.WindowsRuntime)
-                sb.Append(", ContentType=WindowsRuntime");
+                vsb.Append(", ContentType=WindowsRuntime");
 
             // NOTE: By design (desktop compat) AssemblyName.FullName and ToString() do not include ProcessorArchitecture.
 
-            return sb.ToString();
+            return vsb.ToString();
         }
 
-        private static void AppendQuoted(this StringBuilder sb, string s)
+        private static void AppendQuoted(this ref ValueStringBuilder vsb, string s)
         {
             bool needsQuoting = false;
             const char quoteChar = '\"';
@@ -90,7 +92,7 @@ private static void AppendQuoted(this StringBuilder sb, string s)
                 needsQuoting = true;
 
             if (needsQuoting)
-                sb.Append(quoteChar);
+                vsb.Append(quoteChar);
 
             for (int i = 0; i < s.Length; i++)
             {
@@ -101,24 +103,24 @@ private static void AppendQuoted(this StringBuilder sb, string s)
                     case '=':
                     case '\'':
                     case '"':
-                        sb.Append('\\');
+                        vsb.Append('\\');
                         break;
                     case '\t':
-                        sb.Append("\\t");
+                        vsb.Append("\\t");
                         continue;
                     case '\r':
-                        sb.Append("\\r");
+                        vsb.Append("\\r");
                         continue;
                     case '\n':
-                        sb.Append("\\n");
+                        vsb.Append("\\n");
                         continue;
                 }
 
-                sb.Append(s[i]);
+                vsb.Append(s[i]);
             }
 
             if (needsQuoting)
-                sb.Append(quoteChar);
+                vsb.Append(quoteChar);
         }
 
         private static Version CanonicalizeVersion(this Version version)